Grip Strength and Electromyogram (EMG) Biology 111 Experiment 9
Chandra Murali Lab Partner : John Alms 08/06/2011
Abstract
In this EMG experiment the Grip strength of an individual is measured. It shows that a motor neuron and all muscle fibers are initiated when a muscle contraction occurs. All motor units fire when this contraction of the muscle occurs. The muscle strength of the contraction is related to the number of motor units . Changes in the intensity of muscle contraction reflect many factors that may influence the demand that is placed on a muscle in a given situation. One of these factors is that involving the speed of contraction. It has been proposed that increases in the speed of contraction during a concentric contraction necessitate increases in the level of muscle activation. If this is the case, it would appear that such increases would be evident in the amplitude of associated EMG=s. Monitoring of the EMG levels during contractions of various various speeds, then, show variations in the amount of muscle muscle activation. Extrinsic muscles determine the grip strength strength of the hand and is therefore useful in the assessment of the upper extremity, hand function and general strength. In a clinical setting a grip strength can be used to determine the extent of an injury and disease. This is in turn can help in the rehabilitation program to treat the injury and disease.
Purpose The purpose of this lab is two-fold: 1) to introduce and familiarize the student with the necessary equipment needed to collect EMG data; and 2) to e valuate the effects of contraction vel ocity on the
EMG It is also the purpose to test EMG and force as well the fatigue factor in both dominant and dominant arm. It is also to determine how a particular muscle responds appropriately to
stimulation,.EMG is also a test of the motor system. It has to be noted that
The purpose of the
experiment one was to determine which of the muscles, dominant or non-dominant had more electrical activity, (i.e. motor unit recruitment) and whether or not dominant muscles had more force and power as expected, and if the weaker, non-dominant muscle fatigued faster. Rationale:
During muscle contraction, changes in the intensity refle ct many factors that may influence the demand that is placed on a muscle in a given situation. During contractions of various intervals, should show variations in the amount of muscle activation that is the purpose and rationale of monitoring of the EMG levels.
Procedure.
Introduction Methods: Participants: A sample of forty-five students (twenty-five females and seventeen males) ages 18 to 30 years participated in the study. All subjects were enrolled in the Knesiology 2630 Growth, Development and Aging lab at the University of Lethbridge. The average age of the female subjects was 20.6 +/- 1.9yrs, the average age of the male subjects was 21.4 +/- 2.83 years, and the average age of the entire group of subjects was 20.9 +/- 2.33years. Apparatus: A handgrip dynamometer, similar to the one illustrated in figure 1 was used to test the grip strength of the subjects with the results being recorded in a spreadsheet on a nearby computer. All subjects used the same handgrip dynamometer with the handle setting remaining the same for everyone.
Procedure: Before the testing began the subjects were instructed on how to complete the grip strength tests by following the procedures listed on the back of the Lab 1 handout, which each subject receive d a copy. One by one subjects stood in a comfortable position wi th the elbow of the dominant hand flexed at 90 degrees, with the wrists and forearm in a neutral, anatomical position, and the handgrip dynamometer lightly held in the dominant hand so that the needle of the dynamometer was still on 0. When ready the subjects squeezed the dynamometer as hard as possible straightening the elbow if desired but without moving the rest of his/her body. The final grip strength measure for the dominant hand was taken from the dynamometer when the needle no longer moved and was recorded on the computers spreadsheet. The dynamometer was then reset to 0 and the test was repeated with the non-dominant hand. Subjects only completed one trial and all results were recorded on the computer spreadsheet along with their student code, age and gender. Statistical Analysis: Data were summarized into means and standard deviation values using Microsoft Excel. The effect of handedness on grip strength was determined using a paired t-test, and the effect of gender on grip strength was determined using an ANOVA both using SPSS software. Statistical significance was accepted at p<.05. Results: The use of dominant or non-dominant hand (handedness) had a significant effect on grip strength ( t(43)=2.888, p<.05). As indicated in figure 2, grip strength was greatest when the dominant hand was used and least when the non-dominant hand was used. A 2.14 lb. increase in overall grip strength mean was seen when the dominant was used over the non-dominant. Within the female gender, handedness also significantly affected grip strength (t (24)=2.567, p<. 05). Figure 3 illustrates that females had the highest grip strength scores when the dominant hand was used then when the non-dominant hand was used. An increase in the female grip strength mean of approximately 2.16lb was seen when the dominant hand was used. Figure 3 also illustrates that males had greater grip strengths in the dominant hand then non-dominant, an approximate 2.12lb increase was seen when the dominant hand was used. However within the male gender handedness was found to not significantly effect grip strength ( t(16)=1.433, p>.05). Therefore there is no difference in the grip strength of males dominant and non-dominant hands. Lastly, there was a significant effect for gender on dominant grip strength performance (F (1,41)=88.702, p<.05) and on non-dominant grip strength performance ( F(1,41)= 14 8.671, p<.05). Figure 3 illustrates that for both dominant and non-dominant hands males had a significantly higher grip strengths then females. An increase of 21.70lbs was seen in the dominant hand for males as compared to females, and an increase of 21.74 lbs, was seen in the non-dominant hand of males over fem ales. Discussion:
The results of this study indicate that greater grip strength is achieved when the dominant hand was used then when the non-dominant hand was used, as illustrated in figure 2, (p<.05). These findings support the research hypothesis that handedness would have a significant effect on grip strength, with the dominant hand being stronger then the non-dominant. These results are consistent with and provide validation for the work done by Driscoll et. al. (1992); Richards et. al. (1996), and Provins et. al. (1989), all who reported increased grip strength with the dominant hand. These findings discredit the work done by Reikeras (1983) and Harkinen et. al. (1993) who reported that there w as no significant difference in grip strength of the dominant and non-dominant hands. One explanation for the differences in grip strength due to handedness is that the more a hand is used the more the muscles in the hand are used and consequently, the more hypertrophy (increase in muscle size) occurs which therefore leads to increased strength (Robergs & Roberts, 1997). Since the dominant hand is used more often in everyday living activities and sports activities, it should therefore be stronger. In addition, handedness also had a significant effect within the female gender, as illustrated in figure 3 (p<. 05). The highest grip strength was observed with the dominant hand. However this was not the case in the male gender. The results of this study indicated that within the male gender there is not a significant effect between handedness and grip strength. One explanation for this difference is that males are more active in intense activities such as weight training where both hands are used at the same time, therefore hypertrophy and increased muscle fiber size (and as a result strength) is occurring in both the dominant and non-dominant hands simultaneously (Roberg s & Roberts, 1997). The results of the study also indicate that grip strength for males in both their dominant and nondominant hands was significantly higher then the grip strengths for the females, as indicated in figure 3 (p<. 05). These results also support the research hypothesis proposed in this study, that gender will significantly effect grip strength with male grip strength being the greatest. The results are also consistent with those found in studies by Balogun et. al. (1991), Su et. al. (1994), Richards et. al. (1996), Driscoll et. al. (1992) and Harkonen et. al. (1993) all who found that males had greater grip strengths than females. One possible explanation for these findings is due to the type of activity each gender is involved in, for example males are more active in intense activities such as weight training, as mentioned previously, which causes greater hypertrophy of the muscles whereas females are more active in endurance type activities such as aerobics where the hypertrophy isnt as great (Robergs & Roberts, 1997). A second explanation for the difference in gender grip strengths is due to gender differences in physique. Males on average have greater lean body mass (more muscle) which is a major determinant of strength therefore they should have greater grip strengths. Also there is a correlation between height, weight, and grip strength, therefore since males are taller and heavier contributes to there increased grip strength (discussed briefly in introduction). The results of this study therefore conclude that : (1) dominant hands have greater grip strengths then non-dominant and (2) males have greater grip strengths then females. These results have important applications in the use of grip strength in the rehabilitation process or in diagnosing and/ or monitoring the progress of an injury or disease. These results imply that the grip strength of the nondominant hand can not be used as an assessment or monitoring g uide for the dominant hand and vice versa, therefore alternate means of determining the extent of a injury or disease, or the progress of
rehabilitation must be used. Also, knowing the role that handedness plays in grip strength may help us understand why people differ in everyday life activities. This study contained a few limitations that may have influenced the r esults and may influence the interpretation and application of the results. To begin with only University of Lethbridge Knesiology 2630 students were tested so the sample is not representative of the entire population, for at least two reasons, (1) most knesiology students are quite active, and (2) the sample only represents a age cohort of 18-30yrs. Therefore the results cannot be generalized to the entire population. Secondly, even though subjects were given instructions on how to carry out the procedure, the position of many of the subjects arms, for example the angle of their elbow and shoulders, was not kept constant. As a result of differing body positions some subjects may have had an advantage over others resulting in higher grip strength scores. Thirdly, there were more females than males in the sample which may explain why there was no difference seen in the male subjects between dominant and non-dominant grip strengths because there was not a large enough male sample to achieve accurate results. Also, only one trial was performed per subject, since many individuals may not have been familiar with the grip strength test or the procedure they may not have performed as well therefore this study should be repeated using more trials so that the results are more valid. The subjects involvement in activity, and what type of activity theyre involved in was not accounted for. This has an important impact on the results because if for example, more males are involved in free weight lifting and more females are inactive then it provides an explanation for obtaining differences in grip strength among the two. Lastly, previous injury to the hand, wrist or forearm was not taken into consideration. If an individual had been previously injured then his or her results would be lower compared to someone who hasnt had an injury. All these limitations provide a confounding variable to our study and should in, the future be taken into consideration. In the future, the study should be repeated using a sample that is more representative of the whole population to validate that there is in fact a significant effect seen in both handedness and gender on grip strength. The study should be repeated using more male samples to validate that there is in fact no difference between the grip strength in males dominant and non-dominant hands. The study could also be repeated excluding subjects with injurys or disease. Research should also be directed towards why there i s a difference between the dominant and nondominant hand, or between males and females. What physiological or neural factors contribute to these differences? Also the relationship between gender, weight, height and grip strength could be examined, or the relationship between physique (lean muscle mass) and grip strength. One could examine the relationship between gender, activity and grip strength. Studies could be conducted to find out how weak the non-dominant hand is compared to the dominant, for e xample is the grip strength in the non-dominant hand 85% of the grip strength in the dominant. This could be used for therapeutic or rehabilitation purposes. A study could be done to determine whether the effect of handedness and grip strength is significant in specific sport situations such as racquet sports or basketball, etc. Perhaps a pretest/posttest study could be done to determine if grip strength could be made more equal with training. Finally, this study could be repeated using a different technique to measure grip strength to see if the results are consistent. Return to Top.
Sample Lab B - S'00 Grip Strength & Handedness Introduction Our hands are one of the most useful and important instruments that our body has. They are used in so many functions many of which we dont even notice. The dominant hand usually leading the way and the non-dominant often used to assist in bilateral tasks. (Richards, Olson, & Palmiter-Thomas, 1996, p.132) For this reason, we must wonder if the dominant hand would be stronger in a subject matter such as grip strength. We may also wonder if a males or a females grip strength is stronger. There have been various experiments done with grip strength concerning different positions of certain body parts as well as the body as a whole. One such experiment was done to see how forearm position affects grip strength. It found that in each of three positions the left hand was always weaker (all participants were right handed) for both males and females and that males always had stronger grip strength than females. (Richards et al., 1996, p.132) Despite the independent variables, many other experiments had the same general trends. This experiment sets out to find out if there is in fact a difference in grip strength between the dominant and non-dominant hands of males and females. From previous experiments it is anticipated that the results will be similar. Grip strength testing can be a simple way to examine individual and general differences or trends in grip strength. Data such as this can be valuable not only to understanding everyday functions but for people looking at specific areas like the sport of tennis or illness or disease that may have lead to decrepit hands. Method PARTICIPANTS Forty-two students from the Kinesiology 2630 class participated in this study. Of those participants, twenty-five were female aged 18-25 with an average age of 20.6 and seventeen were male aged 19-30 with an average age of 21.4. APPARATUS: A handgrip dynamometer was used to receive the grip strength measurements. The results of the grip strength for the dominant and the non-dominant hands were r ecorded into the computer. PROCEDURE: One at a time, participants each took a turn using the dynamometer. Before beginning the participant ensured the dynamometer was set to zero. While standing comfortably the participant placed the elbow of the dominant hand at 90° of flexion. The handgrip dynamometer was then placed in the dominant hand. When ready, the participant squeezed the dynamometer as hard as he/she could. The measurement was then recorded and the dynamometer was reset to zero. The participant
then conducted the same procedure with his/her non-dominant hand. Each participant conducted one trial for each hand. Results were recorded in terms of age, gender, and the scores for each hand. Results The study showed that for females, only 16% had a higher grip strength in their non-dominant hand and less than 1% had equal strength in both hands, and for males only 35% had a higher grip strength in their non-dominant hand, but on average, the grip strength of the dominant hand was stronger than that of the non-dominant hand for both males and females. The males averaged 49.88 with their dominant hand versus 47.76 with their non-dominant hand. Females averaged 28.18 with their dominant hand in comparison with 26.02 for their non-dominant hand. The study also showed that on average, the male scores for both dominant and non-dominant hands were higher than those for females in the same categories. The male dominant hand average was 43.5% greater than the female average and the male non-dominant average was 45.5% greater than the female non-dominant average. Both of these trends can be seen in Figure 1. Discussion Based on the data collected it can be assumed that this experiment followed a general trend as many previously conducted experiments on the same topic. The experiment did show that the majority and on average males and females had greater grip strength with their dominant hand. Although this does seem to be accurate, perhaps if more trials were run for each hand of each person, then an average could be taken from those values and then a complete average could be calculated and the results would have more support. Also, in the experiment participants were not directed to perform the task in the position recommended by the Ame rican Society of Hand Therapists, the client seated in a straight backed chair with feet flat on the floor (Fess & Moran, 1981), so we may wonder if that would have had an impact, though probably not significantly, on the results. This difference in strength between the two hands could be due to the fact that the dominant hand is more regularly used and used for more strenuous work, whereas in many cases the non-dominant hand is used to aid the dominant. Results also proved that grip strength in males was on average greater than in females. The difference here may be attributed to the simple fact that the male has larg er hands than the female. When taking into consideration the size of the male hands it may be considered that with these large r hands many males perform more strenuous or labor-intensive work that may contribute to b uilding strength.
Grip strength is an important factor when it comes to daily living. If a person had very weak grip strength it could be potentially dangerous. Carrying a pot full of water off of the stove could be dropped and cause various injuries. For a weak mother with a young baby it could be lethal if the mother was ever to drop the infant. Everyday functions we take for granted such as driving or handwriting become more difficult with a weaker grip strength, and in the case of driving, it can become hazardous if one
cannot manuover the steering wheel or gear down quick enough. A simple thing such as grip strength can be overlooked but is in fact important to our he alth. Return to Top. Sample Lab C - S'00 (Introduction only) Introduction The question I wanted to address was whether or not there was a difference in grip strength between dominant and non-dominant hands. I also wanted to determine if there was a significant difference in grip strength between genders. In a study conducted by the National Safety Council it was determined that because women are, on average, smaller and weigh less the average man they also have a weaker grip strength (NSC, 1998). The American Occupational Therapy Association conducted a study on grip strength which showed that generally dominant hands are stronger than non-dominant hands and that males on average have greater grip strength (AOTA, 1999). These studies related to my experiment because they were trying to determine the same characteristics of grip strength. I used the data obtained from the experiment to do an analysis and compared it with my hypothesis. What I expected to find by carrying out this study was that the participa nt=s dominant hand grip strength would be greater than their non-dominant hand grip strength because the dominant hand is used more often and thus becomes stronger. I also expected that, on average, males would have greater grip strength than females for both dominant and non-dominant hands because males generally have more muscle mass, are stronger and it is more characteristic for males to perform labour intensive activities.
