JURNAL SENAM NIFAS

Review

Effect of Postpartum Exercise on Mothers and their Offspring: A Review of the Literature Dawnine Enette Larson-Meyer

Abstract LARS LA RSON ON-M -MEY EYER ER,, DA DAWN WNIN INE E EN ENET ETTE TE.. Ef Effe fect ct of postpa pos tpartu rtum m exe exerci rcise se on mot mother herss and the their ir off offspr spring ing:: a review of the literature. Obes Res. 2002;10:841–853. Epidemi Epid emiolog ologica icall stud studies ies sugg suggest est that chi childbe ldbeari aring ng may cont contrib rib-ute to the development of obesity. In the past 12 years, several cross-sectiona cross-s ectionall and randomized trials have address addressed ed the effect of postpartum exercise on weight loss and/or energy balance in mostly lactating women. These studies suggest that moderate exercise without specific calorie restriction does not promote greater weight or fat loss. This may be because exercise may promote greater energy intake and/or reduced energy expenditure from nonexercise physical activity (thus prevent preventing ing negative energy balance), but further research is needed. Regular exercis exer cise, e, howe however, ver, is lik likely ely to have other imp import ortant ant hea health lth benefits after childbirth. A few published studies suggest that postpartum exercise improves aerobic fitness, high-density lipoprotein-chol poprote in-cholesterol esterol levels, and insulin sensitivity. sensitivity. Exercis Exercisee may als also o enha enhance nce psyc psychol hologic ogical al wel well-be l-being ing,, but cont control rolled led clinica cli nicall stu studies dies are nee needed. ded. Alt Althoug hough h two publ publishe ished d stu studies dies have addressed whether exercise training attenuates lactationinduced indu ced bone loss, bett better er cont control rolled led stu studie diess are need needed ed to determine determ ine whether postpartum weight-bearing weight-bearing exerci exercise se can improve imp rove bone min minera erall dens density ity in lac lactat tating ing and nonl nonlact actati ating ng women alike. In lactating women, several studies have collectively determined that neither acute nor regular exercise has advers adv ersee eff effect ectss on a mot mother her’s ’s abi abilit lity y to suc succes cessfu sfully lly bre breast ast-fe -feed. ed. It needs to be determined whether a woman’s participation in regular exercise after childbirth will improve her ability to mother or instil ins tilll lif lifeti etime me hab habits its of reg regula ularr phy physic sical al act activi ivity ty in eit either her her hersel selff or her offspring. Overall, published studies have established the importance of regular exercise during the postpartum period. More research, however, is needed in this important area. Key words: weight retention, aerobic fitness, bone mineral density, lactation, exercise guidelines

Received for review December 3, 2001. Accepted for publication in final form April 10, 2002. Division of Health and Performance Enhancement, Pennington Biomedical Research Center, Louisiana State University, Baton Rouge, Louisiana. Address correspondence to D. Enette Larson-Meyer, Ph.D., R.D., Pennington Biomedical Research Center, 6400 Perkins Road, Baton Rouge, LA 80808-4124. E-mail: [email protected] Copyright © 2002 NAASO

Introduction Numerous anecdotal (1–3), cross-sectional (4,5), and longitudinal (6 –10) studies suggest that childbearing may be an important impo rtant contributor contributor to the devel developme opment nt of obesi obesity. ty. The averag ave ragee wei weight ght gai gain n ass associ ociate ated d wit with h bea bearin ring g one chi child, ld, however, is surprisingly small and reported to be 0.5 kg above age-associated weight gain in the Stockholm Pregnancy and Weight Development Study (8) and 1.6 to 1.7 kg above age-associated weight gain in The First National Health and Nutrition Examination Survey (NHANES) and The Nat Nation ional al Mat Matern ernal al and Inf Infant ant Hea Health lth Sur Survey vey (5, (5,7). 7). Average weight gain with single parity, however, ignores the fac factt tha thatt som somee wom women en gai gain n con consid sidera erably bly mor moree tha than n averag ave ragee (5, (5,8), 8), and tha thatt thi thiss wei weight ght gain is lik likely ely to be perman per manent ent and com compou pound nd wit with h sub subseq sequen uentt pre pregna gnanci ncies es (11). For example, in the Stockholm Pregnancy and Weight Develo Dev elopme pment nt Stu Study, dy, 14% of the women women gai gained ned 5 kg or more than thei theirr prepr prepregnan egnancy cy weig weight ht (8). The NHANES survey uncovered that having one live birth increased the risk of becoming moderately overweight [body mass index (BMI), 27.3 kg/m2] by 60% and becoming obese (BMI, 2 30.0 kg/m ) by 110% (7). In addition, several studies have found fou nd tha thatt cer certai tain n sub subgro groups ups of wom women en (10 (10), ), esp especi eciall ally y African-American women (9,12,13), are more sensitive to pregnancy-associated weight retention and increases in central fat distribution. In the Coronary Artery Risk Development in Young Adults (CARDIA) study, African-American women in all parity groups gained almost twice as much weight as did white women and had greater increases in the waist-to-hip ratio (9). Thus, certain lifestyle, metabolic, or genetic factors may predispose women of varied ethnicities to retain or even gain weight in the postpartum period. Little Litt le is known conce concerning rning the bene benefits fits of exer exercise cise or increased physical activity in the postpartum period. Nonetheless, regular physical exercise is likely to be as beneficial in the postpartum period as it is at other times in a woman’s life. The possible benefits include the following: 1) preventing obe obesit sity y (or ove overwe rweigh ight) t) thr throug ough h pro promot motion ion of bod body y fat/bo fat /body dy wei weight ght los loss; s; 2) pro promot moting ing aer aerobi obicc fit fitnes nesss and strength, leading to an improved ability to perform activities of mothering; 3) optimizing bone health by increasing bone mineral density (BMD) and/or preventing lactation-associated bone loss; and 4) improving mood or self-esteem. In OBESITY OBES ITY RESEARC RESEARCH H Vol. 10 No. 8 August August 2002 2002

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Postpartum Exercise, Larson-Meyer

addition, a mother’s participation in regular exercise after childbirth may encourage regular physical activity in her offspring. Unfounded concerns, however, are that exercise that is too “strenuous” may tire the mother, and, if she is breast-feeding, may alter the quality or quantity of her milk, both of which may compromise her ability to adequately care for and feed her infant. This paper reviews the literature on the benefits of and concerns about exercise and exercise in combination with lactation in the postpartum period and expands on other recent reviews (14 –17).

Postpartum Exercise and Body Weight, Body Composition, and Energy Balance The majority of studies assessing the influence of postpartum exercise on body-weight issues have been retrospective epidemiological studies that rely on self-reported data. Although the results of these studies are of interest, clinical trials (particularly randomly assigned trials) provide more scientifically interpretable results. Because of concerns that exercise might impair breast milk quantity or quality, most of the clinical cross-sectional (18,19) and randomized trials (20 –22) conducted over the last 12 years have investigated the effect of postpartum exercise on weight retention and/or energy balance in lactating women. Only a few have addressed this question in nonlactating (bottle-feeding) mothers (23,24), who make up the majority (71%) at 6 months postpartum (25). Thus, it may be difficult to make inferences about postpartum women in general, based on results mostly in lactating women. For example, some of the benefits of postpartum exercise may be masked in lactating women because both exercise and lactation can alter metabolism, food intake, and psychosocial well-being. Furthermore, published studies assessing the effect of regular postpartum exercise on energy balance have measured total energy expenditure (TEE) using heart rate monitoring (20) or factorial analysis (19,21), but not using more accurate techniques (i.e., doubly labeled water). Epidemiological Studies Some (26 –28), but not all (12,29), epidemiological-type studies find that women with higher levels of physical activity in the postpartum period are more likely to return to their prepregnancy body weight (26) and retain less pregnancy-associated weight gain (12,27,28) than their less active counterparts. In the Stockholm Pregnancy and Weight Development Study, a combined retrospective and prospective study of body-weight changes during pregnancy and one year postpartum in 1432 Swedish Women, postpartum weight retention was influenced by lifestyle factors that occurred both during and after (rather than before) pregnancy (26). In this study, successful return toward prepregnancy weight was more common in women with regular postpartum leisure time physical activity habits, high lacta842

OBESITY RESEARCH Vol. 10 No. 8 August 2002

tion scores (reflecting duration and frequency of breastfeeding), and regular breakfast and lunch habits (26). In a smaller study of 74 mothers enrolled in the Antenatal Care Project, a randomized controlled trial of antenatal care based in South London (28) found that mothers who felt they exercised less and/or ate more after, compared with before, pregnancy were at greater risk of weight gain in the two-and-a-half-year period after childbirth. A shorter study in 1003 American women also found that women who reported higher levels of physical activity retained less weight (3.9 vs. 5.1 kg) at 6 weeks postpartum than less active women (27) In a few studies, postpartum physical activity was not found to influence postpartum weight loss or weight retention. In a group of 795 women living in Wisconsin, selfreported exercise did not influence weight-loss rate or retained weight at 6 months postpartum (29). In another study of 345 low-income African-American and white mothers participating in the Special Supplemental Feeding Program for Women, Infants, and Children in South Carolina, prenatal, but not postnatal, physical activity was one of several variables that predicted postpartum weight loss at 7 to 12 months postpartum (12). African-American women, however, retained 6.4 pounds more than did white women, a finding that was related to higher mean energy intake and lower prenatal and postpartum physical activity. Finally, in a study of 101 bottle-feeding and 106 breast-feeding women residing in Austin, Texas (the only study accounting for feeding method), Walker and Freeland-Graves (23) found that postpartum weight retention was associated with aerobic exercise in bottle-feeding but not breast-feeding women. Data in the aforementioned studies were collected retrospectively and were not consistently adjusted for socioeconomic factors. In most cases, physical activity was also poorly defined or poorly quantified (26 –29), prepregnancy body weight was obtained via a self-report (12,23,26) or measure during the first trimester (28,29), and feeding method (bottle-feeding vs. breast-feeding) was not taken into account. Variation in the length of postpartum followup, from 6 weeks (27) to 2 years (28), also makes comparisons between studies difficult. Cross-sectional and Prospective Studies Little and Clapp (18) and Lovelady et al. (19) compared the differences in body weight (18,19), body composition (18,19), rate of weight loss (18), energy intake (19), and energy expenditure (19) between breast-feeding mothers who either exercised regularly or did not exercise in the postpartum period. The details of the exercise intervention and characteristics of the groups are summarized in Table 1. In both studies, the mothers were highly trained [indicated by their maximal oxygen uptake ( V O2max)]; one study (19) included a former Iron-Man triathlete and a former Olympic gold-medal swimmer. In the Little and Clapp study (18), the


exercise group (who also exercised during pregnancy) tended to weigh less and have lower body fat stores at 2 weeks postpartum. Between 2 and 12 weeks postpartum, however, the exercisers did not lose more weight than the controls. In the study by Lovelady et al. (19), the exercise group had lower postpartum body fat percentages, gained less weight during pregnancy (12.1 vs. 15.5 kg), and had higher levels of TEE and energy intake than did the control group. This resulted in no difference in the average daily energy deficit between groups. Unfortunately, Lovelady et al. (19) did not make longitudinal measurements to determine postpartum weight or body fat loss. It is possible that exercisers in the Little and Clapp study (18) compensated for their significantly greater energy costs through greater increases in energy intake (i.e., preventing a greater energy deficit), which was noted in the study by Lovelady et al. (19). Another explanation is that because the trained women were already lean (even though they weighed more than their prepregnancy weight), a greater rate of weight loss compared with their slightly overweight counterparts was not realistic. Randomly Assigned Trials In several well-designed studies by Dewey et al. (20), McCrory et al. (21), and Lovelady et al. (22,30), previously sedentary women were randomly assigned to a control group or aerobic-exercise intervention group for 11 days (21) to 12 weeks (20) (Table 1). In the first study, normalweight women who gained 15 kg during pregnancy (15  5.3 kg in the exercise and 17.5  5.4 kg in the control group) were randomly assigned to an aerobic exercise or control group for 12 weeks beginning 6 to 8 weeks postpartum (20,30). Exercise was individualized with choices of brisk walking, jogging, or bicycling for 45 minutes at moderate intensity. Women in the exercise group were found to compensate for the increased energy expenditure of exercise with significantly higher energy intake and, in the latter half of the study, with reductions in nonexercise physical activity (20,30). As a result, TEE, rate of weight loss, or decline in body fat did not differ between groups. The authors suggested that higher levels of TEE may be difficult to sustain because of postpartum fatigue or time constraints (20), and that exercise alone (at least in women with a normal BMI) does not promote weight loss without intentional calorie restriction (30). In a second randomized trial, McCrory et al. (21) looked at changes in milk volume and composition in lactating women partaking in 11 days of 35% calorie restriction by either diet or a combination of diet and exercise. They found that the diet and exercise group experienced a significantly greater reduction in body fat and greater preservation of lean mass than women assigned to the diet-only or control groups. The clinical significance of findings from shortterm calorie restriction, however, are not known.

Most recently, Lovelady et al. (22) looked at the effect of a combination of diet (500 kcal less than predicted TEE) plus exercise compared with no intervention on weight loss and body composition in overweight lactating women (BMI, 28 kg/m2). The investigators found that the combined diet and exercise intervention resulted in significantly greater weight and fat loss compared with the control group. As a result of the intervention, they found that more women in the diet and exercise group (38%) achieved a BMI below 25 kg/m2 as compared with the control group (10.5%). Inclusion of a diet-only group would have strengthened the study and provided information on whether moderate aerobic exercise preserves lean tissue during calorie restriction in overweight lactating women. Other studies find that lean body mass is preserved during lactation in well-nourished women (31), but it is not known whether exercise would promote lean-mass preservation during energy and/or protein restriction. Finally, in the one intervention trial that looked exclusively at nonlactating women, Leermakers et al. (24), assessed the effect of a 6-month behavioral weight-loss intervention that included both exercise and diet components on postpartum weight retention (Table 1). In this randomly assigned trial delivered through correspondence, women in the intervention lost both significantly more weight (7.8 vs. 4.9 kg) and a greater percentage of their excess postpartum weight (79% vs. 44%) than those in the control group. A significantly greater percentage of those in the intervention compared with the control group were also found to return to their prepregnancy weight (33 vs. 11.5%). Although the intervention as a whole was effective, the study did not attempt to assess the influence of exercise intervention without dieting or behavior modification.

Postpartum Exercise and Improvement of Aerobic Fitness and Strength Studies assessing the effect of postpartum exercise on aerobic capacity or strength are limited. In the aforementioned randomized control trials, Dewey et al. (20) and Lovelady et al. (22) found that V O2max increased by 25 and 13%, respectively, in response to the 10 to 12 week exercise intervention. To date, unfortunately, studies have not assessed the effect of strength training (with or without aerobic exercise) during the postpartum period on muscle strength and endurance or the preservation of lean body mass. More importantly, the possible benefit of maternal fitness on the daily physical activities of mothering, including lifting, carrying, or running after a child, are not known.

Postpartum Exercise and Improvement of Maternal Health Bone Content and BMD It is a well-documented phenomenon that lactation results in a temporary loss of BMD. Studies have consistently OBESITY RESEARCH Vol. 10 No. 8 August 2002

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Table 1. Summary of studies addressing the effect of postpartum exercise on changes in body weight, body composition, and energy balance Pre-evaluation subject characteristics Study Reference

design

No. of subjects

Feeding

Weight

status

BMI

Body fat

2

(kg)

(kg/m )

V O2max (mL/kg/min)

(%)

Cross-sectional and prospective studies

Little and Clapp (18)

Selfselected E vs. C

E

Lovelady et al. (19)

Selfselected E vs. C

E

11; 9

Breastfeeding

E



8; 

Breastfeeding

E

C



C



8

64.8  7.8; C  71.6  13.1; NS, E vs. C

E

59.3  3.9; C  57.4  5.7; NS, E vs. C

E







C



C

23.5; 26.1*

E



21.6  4.1; C  25.7  6.6; NS, E vs. C

E



21.1; 20.7*

E

21.7  3.5; C  27.9  4.7; p  0.01, E vs.

E









C

54.1  7.0; C  36.9  5.3; p  0.001, E vs. C 46.4  2.4; C  30.3  4.7; p  0.001, E vs. C

Randomly assigned trials

Dewey and McCrory (73)

Randomized E vs. C

E

18; C  15

Breastfeeding

E

McCrory et al. (21)

Randomized Short-term DE and D vs. C

DE  22; D 22; C  23

Breastfeeding

DE  69.0  12.8; D  68.3  10.2; C  68.5  8.5; NS, DE vs. D vs. C

DE  25.5; D  25.1; C  24.7; NS, DE vs. D vs. C

DE  32.9  6.5; D  32.5  6.2; C  32.0  7.0; NS, DE vs. D vs. C

DE  34.2  5.6; D  34.7  5.4; C  33.4  6.3; NS, DE vs. D vs. C

Lovelady et al. (22)

Randomized DE vs. C

DE  21; C  19

Breastfeeding

DE  75.9  9.3; C  76.8  7.8; NS, DE vs. C

DE  27.6  2.4; C  28.0  2.1; NS, DE vs. C

DE  33.8  3.3; C  33.2  4.0; NS, DE vs. C

DE  35.1  3.5; C  35.2  5.4; NS, DE vs. C

Leermakers et al. (24)

Randomized DE vs. C

DE  36; C  26

Formulafeeding

DE  76.8  10.0; C  81.1  15.4; NS, DE vs. C

NR

NM

NM



67.3  10.2; C  67.0  7.6; NS, E vs. C



E

25.3; C  23.8*



E

31.5  5.6; C  31.1  5.1; NS, E vs. C



E

27.0  4.8; C  27.6  28.9; NS, E vs. C



BMI, body mass index; V O 2 max, maximal oxygen uptake; MR, metabolic rate; E, exercise; NM, not measured; C, control; NR, not reported; FFM, fat-free mass; NS, not significantly different; HRmax, maximal heart rate; HR, heart rate; DE, diet plus exercise; D, diet alone; NA, not available; PA, physical activity; FF, food frequency. *Statistical significance not reported. † Statistically significant with intervention.

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Table 1. Continued Total energy cost

Exercise intervention

Total energy

(including

Exercise

Weight loss

Body fat change

Resting MR

expenditure

milk energy)

Energy intake

duration

(kg)

(%)

(kcal/d)

(kcal/d)

(kcal/d)

(kcal/d)

NM

NM

NM

NM

3169  273; C 

3-day weighed food records: E 

2398  214; p  0.01,† E vs. C

2739  309; C  2051  335; p  0.01,† E vs. C

2708  405; C  2593  392; NS,† E vs. C

3-day weighed food records: E  2497  436; C  2168  328; p  0.05,† E vs. C

50% V O 2 max, 3 First 3 months d/wk for 20 min/ postpartum session; C  exercised 3 d/wk for 20 min

E



E



70% of predicted HRmax, 5 d/wk for

E

1.8 kg; Skinfolds C  2.7 kg; (5 sites) NS,† E vs. Change NR C



For 6 months before study

NM

NM

E

C

88

 23 min/day; C no scheduled exercise

60–70% of HR 12 weeks reserve, 5 d/wk for (starting 6 45 min/session; C  to 8 wks no aerobic exercise postpartum) 1/d/wk



DE  35% energy deficit: 60% by diet restriction, 40% by additional exercise (50–70% V O2 max); D  35% energy deficit; C  maintain usual activity patterns E

E

11 days

E

1.6 kg; Hydrostatic E  1334  126; C  1.6 kg; weighing: E  C  1304  NS† 1.5%; 135; NS,† decrease; C  E vs. C 1.7% decrease; NS,† E vs. C



DE  1.6  0.5; D  1.9  0.7; C  0.2  0.6; p  0.0001, † DE vs. C; NS,† D vs. DE

Densitometry: NR between DE  1.6  groups 1.5 decrease; D  0.9  0.9 decrease; C  0.5  1.6 decrease; p  0.05,† DE DC

Factoral method: E  2631  234;

E

C  1904  196; p  0.001, † E vs. C



HR monitoring: E  2202  365; C  2054  349; NS,† E vs. C

E

NM with intervention

NM with DE  2075  301; intervention D  1874  232; C  NA; NS,† DE vs. D





65 to 80 of HR 10 weeks reserve 4 d/wk for (postpartum 45 min/session; D  weeks 5 to 500 kcal  14) predicted; C  instructed not to exercise or restrict food intake

DE  4.8  Hydrostatic 1.7; C  Weighing: DE 0.8  2.3;  3.3  1.8% decrease; C  p  0.01,† DE vs. C 0.2  1.8% decrease; p 

walking 2 miles/ 6 months day  5 days/wk; D  1000–1500 kcal, 20% fat; C  given instructional brochure about healthy eating and exercise

DE  7.8  4.5; C  4.9  5.4; p  0.03†





1348  115; 1274 



157; NS† when adjusted for body mass or FFM



E



NM

NM

NM

3-day weighed food record: DE  1669  293; C  2142  540; NS,† DE vs. C

NM

Total NM; PA via questionnaire: DE  1000 kcal/wk; C  1229 kcal/wk; NS,† DE vs. C

NM

Block FF Questionnaire: DE  1331; C 1340; NS,† DE vs. C

0.01,† DE vs. C NM




845


found changes in axial bone loss ranging from 3% to 9% over periods of time as short as 2 to 6 months (32 –35). Appendicular bone or total body BMD, however, is not affected. It is speculated that changes in axial bone result from the prolonged lactation-induced estrogen deficiency combined with the “calcium drain” of breast-feeding (18) (an additional 200 to 400 mg/day of calcium is required during lactation). These changes in BMD, however, are generally considered a physiological response to lactation and are not found to be influenced by a calcium intake greater than the recommended dietary allowance (32,36). The site-specific differences in bone likely reflect higher metabolic turnover in trabecular bone of the axial skeleton (18), but could also be related to changes in mechanical stress resulting from weight gain, posture, and/or activity (37). Only two published studies have addressed whether postpartum exercise reduces lactation-induced bone loss. In a small longitudinal study, Drinkwater and Chesnut (37) followed six athletes who had been running an average 32.8 miles/wk before pregnancy and had continued to exercise during both pregnancy and postpartum. At 1 month postpartum, BMD was decreased in the femoral neck ( p  0.05), radial shaft ( p  0.05), and lumbar vertebrae ( p  0.06) compared with the prepregnancy state. BMD continued to decrease in the femoral neck at 6 months postpartum, but returned to prepregnancy values in the radial shaft and lumbar vertebrae. Unfortunately, the investigators did not include a control group or quantify the intensity, duration, or frequency of the exercise regimen. They mention only that women continued to exercise during pregnancy and lactation and that most switched from running to walking and/or swimming during the third trimester of pregnancy. In another study, Little and Clapp (18) measured BMD in 20 lactating women within 2 weeks of and between 12 to 14 weeks after parturition. Women who exercised at least 3 days/wk for at least 20 minutes at an intensity 50% of V O2max were retrospectively classified as exercisers and compared with control women who exercised less. BMD decreased in the lumbar spine by 5.4% in the control group and 4.1% in the exercise group, and in the femoral neck by 2.7% in the control and 2.8% in the exercise group, respectively; BMD reductions were not statistically different between groups. The investigators felt, however, that the duration of the study may have been too short, that the stress of the exercise may have been insufficient (given the hypoestrogen state of lactation), and/or that the exercise intensity, frequency, duration, or mode may have been too variable to detect an effect. Also, categorization of groups may not have been distinct enough (because many women in the control group exercised occasionally), and calcium intake and body weight tended to be lower in the exercisers. Randomly assigned clinical studies are needed to further address not only the potential effect of exercise on the 846


attenuation or prevention of lactation-associated bone loss (particularly at sites with a high lactation-associated turnover) but also on the long-term health of women. For example, most studies find that bone loss recovers in healthy women with the cessation of lactation and return of normal menses (32–34). It is also important to determine whether postpartum weight-bearing exercise could ultimately result in improved BMD in both lactating and nonlactating women. Lipoprotein Profile and Insulin Sensitivity Lovelady et al. (20,30) investigated the effect of postpartum exercise on lipoprotein profile and insulin and glucose response to a test meal (20% protein, 30% fat, and 50% carbohydrate) They found that whereas plasma triglycerides, total cholesterol, and low-density lipoprotein-cholesterol decreased during lactation in both exercising and nonexercising women (30), the 12-week aerobic exercise intervention did not further impact serum lipid or fasting insulin concentrations. The exercise group, however, did experience a significant improvement in insulin response to the test meal and a marginal increase in high-density lipoprotein-cholesterol concentration that was not noted in the control group. Improvement was greatest in women with the greatest improvement in V O2max. Because subjects in this study, on average, were not overweight or insulin resistant, further studies in postpartum women who display these characteristics are of interest. Mental Stress and Postpartum Depression The benefits of exercise on psychological health has been widely researched (38 – 41). Most studies find that participation in sports or exercise, or regular physical activity has a positive effect on mental health including reduced symptoms of anxiety and depression and increased general wellbeing. Some studies have suggested that the benefit of physical activity on reducing anxiety and depression (38,40) and increasing positive mood and general well-being (39 – 41) are stronger in women than men (41). In 1000 women, Sampselle et al. (27) recently evaluated the psychosocial well-being during the prenatal and postpartum period using Lederman’s postpartum maternal adaptation questionnaire, a reliable and valid tool that assesses seven subareas specific to the postpartum condition including: 1) quality of partner relationship; 2) perception of partner ’s participation in childcare; 3) gratification from labor and delivery experience; 4) satisfaction with life circumstances; 5) confidence in ability to cope with tasks of motherhood; 6) satisfaction with motherhood and infant care; and 7) support for maternal role from family and friends. At 6 weeks postpartum, women who exercised vigorously had better scores in all subareas, which were statistically significant for all but one area (support from friends and family). Unfortunately, although the investigators attempt to adequately control psy-


chosocial variables, “vigorous exercise” was never defined. In another study, Koltyn and Schultes (42) evaluated the acute effect of a single 60-minute aerobic exercise session (60% to 70% of heart rate reserve) in 20 women between 6 and 20 weeks postpartum. Women randomly assigned to the exercise group ( n  10) experienced decreased state anxiety, depression, and total mood disturbance and increased vigor after the exercise session, but only mood and vigor were significantly improved compared with the control group (n  10), who rested for 60 minutes. Little is known concerning whether regular exercise decreases the prevalence or severity of postpartum depression. Studies, however, are of interest because it is estimated that 13% of women experience some degree of postpartum depression (43). Preliminary findings from the nonrandomized, longitudinal studies of Clapp (44) suggest that the incidence of significant postpartum depression is lower in exercising women compared with active controls. Although it could be argued that less depressed women may be more likely to exercise, Clapp hypothesizes that depression occurs less in exercising women because exercise gives them a regular break from the 24-hour, 7-day-a-week commitment that comes with a new baby. Subjectively, Clapp describes exercising postpartum women as appearing less overwhelmed and more ready to master motherhood. Clapp has also reported that exercising women have more positive attitudes about their bodies during and after pregnancy than do nonexercising women (44). This is important because the psychological effects of excess weight or fear of obesity can affect mental health during the postpartum period (45). According to one study, 70% of postpartum women are dissatisfied with their bodily appearance at 6 months, and 39% are dissatisfied at 1 year (46). Twenty-five percent also report decreased intercourse because of feeling unattractive because of weight gain.

Postpartum Exercise and Quantity and Quality of Human Breast Milk Volume and Macronutrient Composition of Breast Milk A number of studies have investigated whether an acute bout of (19,47,48) or regular participation in (19 –22) exercise influences either volume or composition of breast milk. These studies have found no adverse effects of exercise on milk volume or macronutrient composition when exercise is performed either alone (19,20,47,48) or with caloric restriction (21,22). Over the short term, Carey et al. (47) and Quinn and Carey (48) found that volume and lipid composition of breast milk was not affected by graded maximal exercise to exhaustion (47,48) or 30 minutes of moderate to hard submaximal exercise (47,48) when compared with a control session. (Comparison with the same time-points during a control session is important because milk volume decreases progressively during the measurement period). Long-term participation in an exercise program was found to have no affect on volume (adjusted for infant ’s

weight), energy density or energy composition (protein, lipid and lactose) of breast milk in non-overweight women training vigorously (19) or randomly assigned to an exercise intervention (20), or in overweight women randomly assigned to an exercise and calorie-restriction intervention (22). These studies also found no differences in body weight (19,20,22) or growth (20,22) among infants whose mothers were in either the exercise or control groups. Mineral Composition of Breast Milk In 14 postpartum women, Fly et al. (49) determined that short-term maximal graded exercise does not alter the concentration of phosphorus, calcium, magnesium, sodium, or potassium in breast-milk samples obtained before and at 10, 30, and 60 minutes postexercise compared with a control period when the subjects rested for 30 minutes. Although long-term studies on the effect of exercise training on mineral composition in breast milk have not been conducted, it seems unlikely that regular exercise would alter mineral composition of breast milk because mineral composition is not influenced even by mineral intake (50). Immunological Properties of Breast Milk Because research has suggested that general immune response to exercise is enhanced by moderate exercise but depressed by strenuous training, Gregory et al. (51) investigated whether a bout of maximal exercise would effect immunoglobulin A (IgA) concentrations in breast milk. Secretory IgA, the predominant immunoglobulin present in colostrum and mature breast milk, is composed of approximately equal amounts of subclasses IgA1 and IgA2, which seem to have functional and proteolytic susceptibility differences (52). IgA1 antibodies are stimulated primarily by protein and carbohydrate antigens, whereas IgA2 antibodies are induced by lipid-containing antibodies. IgA1 can also be degraded by proteases produced by mucosal pathogens including many dwelling in the infant gastrointestinal tract, whereas IgA2 is apparently protected from these proteases. In 17 physically active women (between 2 and 6 months postpartum), Gregory et al. (51) found that total IgA and IgA1 concentrations were depressed in breast milk sampled 10 and 30 minutes after a maximal graded treadmill test (by  60% to 72% for total IgA and 18% for IgA1) compared with a resting control condition, but returned to baseline concentrations by 60 minutes postexercise. IgA2 concentration was not affected. Quite surprisingly, the investigators concluded that transient depressed levels of IgA make breast milk less beneficial after maximal exercise (51). Their work, however, has been highly criticized (14 – 16,53). Most importantly, the techniques used to measure IgA may have been faulty (values for total IgA were 1 to 2 orders of magnitude lower than typical values) (15). Even if OBESITY RESEARCH Vol. 10 No. 8 August 2002

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Table 2. Summary of studies addressing the influence of maximal and submaximal exercise on human-milk LA concentration

Authors

n

Exercise

Exercise characteristics

V O 2max (mL/kg/min)

Maximal exercise Wallace and Rabin (59)

7

Graded treadmill

Exercised postpartum

NR

Wallace et al. (60)

23

Graded treadmill

Exercised during pregnancy and postpartum

37.2  9.5 (full group); 35.1  8.5 (empty group)

Wallace et al. (54)

26

Graded treadmill

Exercised during pregnancy and lactation, 2 to 6 months postpartum

35.1



9.2

Wallace et al. (61)

23

Graded treadmill


36.5



9.0

9

Graded treadmill

Mild to moderately active

34.7



6.7

12

Graded treadmill


36.4  6.1 (HCHO Group); 34.4  4.5 (MCHO Group)

23

Typical exercise at 55% of HRmax (modified Karvonen formula)


36.5



9.0

50% V O 2 max for 30 minutes 75% V O 2 max for 30 minutes

Mild to moderately; active As above

34.7



6.7

20% below lactate threshold for 30 minutes


At lactate threshold for 30 minutes

As above

Carey et al. (47) Quinn and Carey (48)

Submaximal exercise Wallace et al. (61)

Carey et al. (47)

Quinn and Carey (48)

9

12

As above 36.4  6.1 (HCHO Group); 34.4  4.5 (MCHO Group) As above

LA, lactic acid; V O 2 max, maximal oxygen uptake; NR, not reported; post, postexercise; HRmax, maximal heart rate; HCHO, highcarbohydrate group; MCHO, medium-carbohydrate group. * Measured at limited times.

valid, the investigators failed to discuss that overall reduction in total IgA amounted to a 10% reduction over a 24-hour period (53). Further research in this area has not been conducted.

848


Accumulation of Exercise Byproducts in Breast Milk Wallace et al. (54) were the first to investigate whether exercise would cause an accumulation of lactic acid in breast milk. Interest in this area was based on anecdotal


Table 2. Continued Breast milk LA concentration Blood LA peak

Baseline

6.5 mM at 10 minutes post

0.79 mM

NR

0.8 mM

NR

0.67



0.28 mM

0.64



0.18 mM

Measurement times

Peak

Baseline, 10, 30 minutes post Baseline, 10, 60, 90 minutes post

1.62* mM at 10 minutes post

Baseline, 10, 30 minutes post Baseline, 10 minutes post

3.97

3.5 mM at 10 minutes post with full breasts; 30 minutes with empty breasts 

0.84 mM at 30 minutes

2.88*  0.80 mM at 10 minutes post


0.13 mM

Baseline, 0, 30, 60, 90 minutes post


10 mM at 0 minutes post

0.19 mM

Baseline, 0, 30, 60, 90 minutes post Baseline, 10 minutes post


0.61



0.14 mM

1.06*  0.14 mM at 10 minutes post


0.14 mM




0.14 mM




0.17 mM




0.17 mM



reports from several women who expressed having difficulty nursing after exercise, and results from a preliminary survey that found 4 of 58 women surveyed reported their infants “often” had difficulty nursing after maternal exercise (55). Lactic acid may have initially been tar-

geted among other metabolites that increase with exercise (e.g., hydrogen ion, ammonia, etc.) because it produces a sour taste in adults (56) and readily diffuses into the water compartments of the body (57) (making it likely to diffuse into breast milk). Complaints of difficulty with OBESITY RESEARCH Vol. 10 No. 8 August 2002

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nursing after exercise reported by Wallace ’s group, however, have not been found by other investigators (14,27,44,58). Results of studies investigating the effect of exercise on lactic-acid accumulation in breast milk after both maximal and submaximal exercise are summarized in Table 2. In a series of experiments, Wallace et al. (54,59 – 61) found that breast-milk lactic acid increased between 105% and 493% after graded treadmill exercise until exhaustion and peaked 10 to 30 minutes postexercise (54,59,60). They also found that lactic acid was significantly elevated (by 36%) in samples obtained 10 minutes after a “typical” submaximal workout (45 minutes of running or aerobic dance) (61). Although the average concentration of breast-milk lacticacid concentration was 1.06 mM after submaximal exercise, 17% of the women had peak lactic-acid concentrations that were 1.5 mM. Wallace et al. (54) also found that the mother’s perception of her infant’s acceptance of breast milk was lower after, compared with, before exercise (rating, 2.25 vs. 3.5, respectively). Breast-milk samples were warmed to body temperature and administered through an eye-dropper in double-blind fashion. An infant ’s acceptance was given a score between 1 to 9 (1  cry; 3  reject; 5  indifferent; 7  accept; 9  laugh) and rated using a specially designed (but not validated) scale. Based on previous findings in adults that suggest the taste threshold for lactic acid in water medium is 1.6 mM (56), the authors concluded that maximal and submaximal exercise can result in lactic acid accumulation in breast milk that is high enough to “sour” the taste of the milk and cause the infants to reject it (61). In agreement with Wallace et al. (54,59 – 61), Carey et al. (47), and Quinn and Carey (48) have found significant increases in breast-milk lactic-acid concentration immediately after maximal exercise to exhaustion, increases that approach 650% above pre-exercise concentrations. Peak concentrations in their studies, however, are found to be much lower and reach an average of between 0.94 mM (47) and 1.4 mM (48). Lactic acid has also not been found to accumulate in breast milk after a 30-minute treadmill run at light to moderate intensity and increase only slightly at a more strenuous submaximal pace (Table 2) (47,48). Preliminary results from this group have also established that infant acceptance of breast milk is not reduced after submaximal or maximal exercise when milk is provided in a familiar bottle as evaluated by both the mother and a trained blinded observer (by videotape) (14,62). Studies in which the mother directly breastfeeds her infant after exercise are needed and underway at the University of New Hampshire (14). As reviewed above, the two laboratories (Carey and Wallace’s groups) that have published results on the effect of exercise on breast-milk lactic-acid concentration have come to different conclusions. Preliminary findings from a third 850


laboratory (44), however, agree with the findings of Carey ’s group (14,47,48,62) and suggest that unless exercise intensity is high (above the anaerobic threshold), there is little change in breast-milk lactic acid concentration. Nonetheless, it raises concern that breast-milk lactic acid concentration reported in the published studies are drastically different (Table 2). Wallace et al. (54,59 – 61) report resting lactate concentrations of 0.6 to 0.8 mM, which increase to between 1.6 and 4.0 mM, whereas Carey et al. (47) and Quinn and Carey (48) report resting concentrations of 0.15 to 0.2 mM that increase to between 0.94 and 1.4 mM, respectively. These differences in lactic-acid concentration could be attributable to differences in subject fitness level, but are most likely accounted for by differences in laboratory methodology. For example, V O2max of subjects studied by both groups was similar (Table 2), and breast-milk lactic acid concentration was not found to correlate with V O2max (47) or carbohydrate intake. On the other hand, Wallace et al. (54,59 – 61) assayed lactic acid from thawed milk samples that were deproteinized with perchloric acid and frozen until analysis, whereas Carey ’s laboratory (47,48) assayed lactic acid in fresh whole-milk samples immediately after collection. The significance of these differences is that 1.6 mM concentration is thought to be the threshold for the detection of a sour taste in milk (56). Only a few studies have investigated whether other metabolites accumulate in postexercise breast milk. In the series of experiments described previously, Carey et al. (47) and Quinn and Carey (48) analyzed breast-milk samples for changes in pH, urea, ammonium, and lipid content. They found that exercise did not affect breast-milk pH (47,48), urea (47), ammonium (47), or lipid concentrations (47) in the 90-minute period after submaximal or maximal exercise. The importance of further studies addressing the possible accumulation of other metabolites in postexercise breast milk is illustrated in a case report by Duffy (63) describing an exclusively breast-fed baby who cried inconsolably shortly after nursing after his mother ’s 5-mile run. Lactic acid was ruled out as a cause of apparent stomach cramps because its concentration in the mother ’s milk was not influenced by her 5-mile run. Unfortunately, no other metabolites were measured.

Postpartum Exercise and Influence on Offspring Physical Activity The mother’s participation in regular exercise after childbirth may encourage regular physical activity habits in her offspring. In a handful of studies assessing the correlates of childhood physical activity, parental exercise was found to influence the offspring’s level (64 – 66) or frequency of physical activity (67) and/or physical fitness (68). Some studies have determined that parental exercise habits are more influential in female than male children (67), although


whether habits of the mother or father (or both) are more influential is not conclusive. Different family-dynamic patterns, however, make it difficult to assess the importance of parental habits. A study conducted from 1982 to 1983 on 1562 college-age students found that the reported exercise habits of their fathers, and not their mothers, were associated with physical activity levels of both male and female college students (69). The lack of correlation with the mother’s exercise habits may be related to the era because during the 1960s and 1970s (when these children were growing up), mothers were not encouraged to exercise. On the other hand, two recent studies using more detailed assessments of physical activity levels support the importance of the mothers’ activity pattern on those of her children (64,66). In a study of 129 obese and 142 normal-weight controls and their parents, Fogelholm et al. (64) found that parental inactivity, assessed by 3-day physical activity records, was a strong predictor of childhood inactivity and that this relationship was stronger for the mother’s than for the father’s inactivity. In the Framingham Children’s Study, physical activity was assessed using accelometry in 100 4to 7-year-old children and 99 and 92 of their mothers and fathers, respectively (66). Children of active mothers were two times as likely to be active compared with children of inactive mothers, whereas children of active fathers were 3.5 times as likely to be active. The odds ratio that children of two active parents would be active was 5.8 times that of children with inactive parents. The possible mechanism by which the parents’ activity levels influences the child ’s include parental role modeling, sharing of activities by family members, parental support of children’s physical activity, and genetically transmitted traits. Promoting regular physical activity habits in children could reduce the child’s long-term risk for chronic disease including coronary artery disease, hypertension, type II diabetes, and osteoporosis. Sallis et al. (70), however, feel that because health benefits derived through physical activity are transitory, the major rationale for promoting regular physical activity in children is to facilitate the carryover of habits into adulthood. Although future studies in this area are of interest, it could be speculated that development of regular exercise habits during the postpartum period (when a women is extremely busy) should carryover to her continuing these habits and promoting them in her offspring.

Practical Guidelines for Postpartum Exercise Little data on which to base guidelines for postpartum exercise are available. Nonetheless, The American College of Obstetricians and Gynecologists developed guidelines for postpartum exercise that follow from critical analysis of available physiological data in the perinatal period (71). These guidelines, however, simply state that many of the physiological and morphological changes of pregnancy persist 4 to 6 weeks postpartum and recommend that prepreg-

nancy exercise routines should be resumed gradually based on the woman’s physical capabilities. From their research and the current exercise recommendations, a number of investigators have also published general guidelines (15,44,48,51,72,73). Clapp has developed guidelines for both the initial 6 weeks and the year after parturition (44). He suggests the main goal of exercise in the initial 6 weeks is to obtain personal time and redevelop a sense of control and recommends the following: 1) beginning slowly and increasing gradually; 2) avoiding excessive fatigue and dehydration; 3) supporting and compressing the abdomen and breasts; 4) stopping to evaluate if it hurts; and 5) stopping exercise and seeking medical evaluation if experiencing bright red vaginal bleeding heavier than a menstrual period. He adds that if it feels good, it probably is, and then suggests the goal of the exercise regimen in the remainder of the first year after birth is to improve physical fitness and status. In their guidelines, Dewey and McCrory (73) and McCrory (15) stress that women beginning a postpartum exercise program should obtain medical clearance, begin slowly and progress gradually, and maintain adequate fluid intake—particularly if breast-feeding. McCrory (15) also recommends that women exercise aerobically for 3 to 6 days/wk for 25 to 60 minutes, supplement with muscle toning exercises, and be creative if it is occasionally necessary to exercise with children. Guidelines specifically related to exercise during lactation have been suggested. Wallace et al. (51,72) have suggested that it may be necessary for lactating women to exercise at low intensities to prevent accumulation of lactic acid in breast milk. They also suggest that women nurse before exercise or collect pre-exercise milk for later consumption and discard milk produced during the first 30 minutes postexercise. Carey and Quinn (53) have challenged these recommendations, questioning whether research really suggests that nursing postexercise is harmful to babies and worth the effort of pumping and discarding postexercise milk. In contrast, Quinn and Carey (48) recommend that women who exercise during the early postpartum period (3 to 4 months) use the 6-to-20 Rate of Perceived Exertion scale to maintain an intensity below the level of “hard” (i.e., 12). This recommendation is based on their finding that lactic acid does not accumulate in breast milk when exercise is at an intensity at or below this level. Nursing or expressing milk before exercise and wearing an exercise bra with good support have also been suggested to increase comfort during exercise (15).

Summary and Future Direction More research on the benefits of postpartum exercise is needed, particularly in nonlactating women. Published studies suggest that postpartum exercise has the capacity to improve aerobic fitness (20,22), high-density lipoprotein-cholesterol level (30), insulin sensitivity (30), and psychological wellOBESITY RESEARCH Vol. 10 No. 8 August 2002

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being (27,42). It is not conclusive, however, whether postpartum exercise promotes greater body-weight or body-fat loss after childbirth. In exclusively lactating women, regular exercise has not been shown to promote greater weight loss, a finding that seems to be attributable to exercise also promoting greater energy intake and reducing nonexercise physical activity. On the other hand, a number of studies have collectively suggested that aerobic exercise has no adverse effects on mothers’ ability to successfully breast-feed their infants (19 – 22,47,48). Research is needed to determine whether postpartum exercise can influence maternal bone health, maternal lifetime exercise patterns, or offspring’s physical-activity level. Because becoming a parent is a reason for abandoning exercise, further studies in this area are warranted.

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