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1 EFFECTIVENESS OF THE 1RM ESTIMATION METHOD BASED ON ISOMETRIC SQUAT USING A BACK-DYNAMOMETER SHINICH DEMURA,1 KAZUYOSHI MIYAGUCHI,2 SOHEE SHIN,3 AND YU UCHIDA4 1 Kanazawa University Graduate School of Natural Science & Technology, Kakuma, Kanazawa, Ishikawa, Japan; 2Ishikawa Prefectural University, Suematsu, Nonoichimachi, Ishikawa, Japan; 3Kanazawa University Graduate School of Natural Science & Technology, Kakuma, Kanazawa, Ishikawa, Japan; and 4Kanazawa University Graduate School of Natural Science & Technology, Kakuma, Kanazawa, Ishikawa, Japan ABSTRACT INTRODUCTION T Demura, S, Miyaguchi, K, Shin, S, and Uchida, Y. Effectiveness of he squat is a representative training method to the 1RM estimation method based on isometric squat using a back- improve muscular strength of lower limbs and is dynamometer. J Strength Cond Res 24(10): 27422748, a useful index of lower muscle strength (2,6,8,9,25). 2010This study aimed to clarify the relationships between When performing a squat, we must know the isometric squat (IS) using a back dynamometer and 1 repetition 1 repetition maximum (1RM: the greatest amount of weight that can be lifted with proper technique for only 1 repetition) maximum (1RM) squat for maximum force and muscle activities and to establish an exercise program or to evaluate strength. to examine the effectiveness of a 1RM estimation method based on Because the 1RM test does not require expensive equipment IS. The subjects were 15 young men with weight training and reflects dynamic strength, which is necessary in experience (mean age 20.7 6 0.8 years, mean height 171.3 6 competitive sports, most strength and conditioning profes- 4.4 cm, mean weight 64.4 6 8.4 kg). They performed the IS with sionals have used it as a maximal strength test. various stance widths and squat depths. The measured data of Until now, the direct measurement technique or the exerted maximum force and the action potential of the agonist indirect measurement technique has been used to detect muscles were compared with the 1RM squat data. The exerted personal 1RM. The former examines the maximum weight maximum force during IS was significantly larger in wide stance that can be lifted once. On the other hand, the latter estimates (140% shoulder width) than in narrow stance (5-cm width). The 1RM from the repetition number based on the %1RM maximum force was significantly larger with decreased knee flexion. repetition relationship by using arbitrary submaximal weight As for muscle activity, the % root mean square value of muscle (4). Because the direct measurement technique uses a heavy electric potential of the rectus femoris and the vastus lateralis weight, the risk of injury is high. In particular, when persons tended to be higher in wide stance. As for exerted maximum force, without regular training experience lift weights .90%1RM, their posture becomes unstable (16). As for the indirect wide stance and parallel depth in IS showed a significant and high measurement technique, results differ with the tested correlation (r = 0.73) with 1RM squat. Simple linear regression muscles. For instance, resistance-trained athletes may be analysis revealed a significant estimated regression equation [Y = able to exceed the number of repetitions usually listed in the 0.992X + 30.3 (Y:1RM, X:IS)]. However, the standard error of an table at any given percent of their 1RM, especially in lower- estimate value obtained by the regression equation was very large body core exercise (10,11). On the other hand, subjects may (11.19 kg). In conclusion, IS with wide stance and parallel depth not be able to perform as many repetitions of exercises may be useful for the estimation of 1RM squat. However, estimating involving smaller muscle areas (21,24). a 1RM by IS using a back dynamometer may be difficult. Blazevich et al. (3) reported that isometric squat (IS) with an isometric rack showed significant and high correlation KEY WORDS 1RM squat, isometric, back dynamometer, (r = 0.77) with 1RM squat. Hence, we hypothesized that estimation method although muscular contraction styles differ, IS is an effective index to estimate a 1RM squat. However, because Blazevich Address correspondence to Kazuyoshi Miyaguchi, [email protected] et al. (3) used a large-scaled measurement approach with plala.or.jp. a force plate, it is difficult to use it in a real training scenario. 24(10)/27422748 Therefore, we devised a method using a back dynamometer Journal of Strength and Conditioning Research to measure squat ability easily. Because the back dynamom- 2010 National Strength and Conditioning Association eter is relatively cheap and generally available, using it for the TM 2742 Journal of Strength and Conditioning Research Copyright National Strength and Conditioning Association Unauthorized reproduction of this article is prohibited.
2 the TM Journal of Strength and Conditioning Research | www.nsca-jscr.org a field test may be useful. In particular, the above method may be a useful index of muscle strength for young people without weight training experience. TABLE 1. Physical characteristics (n = 15). However, the back dynamometer was not designed to M SD measure an IS squat. Hence, when performing an IS while shouldering a shaft connected to a back dynamometer, the Age (y) 20.7 0.8 movement may differ from a real squat movement. Thus, we Height (cm) 171.3 4.4 Weight (kg) 64.4 8.4 need to examine relationships between the IS using a back Training experience (y) 2.7 1.6 dynamometer and the 1RM squat for maximum force and Squat 1RM (kg) 99.1 15.7 muscle activities. There have been several reports comparing different forms of squats (5,7,13,18,20,22,23,27). For example, Caterisano et al. (5) reported that in deep knee flexion, the relative contribution of the gluteus maximus is high. Additionally, Wretenberg et al. (28) stated that it is necessary to squat down until reaching a parallel position (the front of thighs are parallel to the ground) to place a large dynamic burden on the leg muscle groups. Also, they reported that exerted maximum force and muscle groups stimulated by the movement forms may differ. However, for IS, there has been little examination of the influence of different movement forms on maximum force and muscle activities. When considering the practical application of the 1RM estimation method using IS, maximum force and muscle activities in a similar measurement posture will be necessary. This study aimed to clarify the relationships between IS and 1RM squat for maximum force and muscle activities and to examine the effectiveness of the 1RM estimation method based on IS. Figure1. Measuring equipment. METHODS Experimental Approach to the Problem The maximum force exerted and muscle groups stimulated by a squatting movement may differ. Thus, when considering the practical application of the 1RM estimation method using IS, we need to examine relation- ships between IS using a back dynamometer and a real 1RM squat for maximum force and muscle activities. We examined the differences of the above measurements in both condi- tions of stance width and squat depth. Furthermore, a regres- sion equation to estimate a 1RM squat value was calcu- lated from the IS value. Subjects The subjects were 15 young men with weight training expe- Figure 2. Schematic representation of experimental setup. rience. Table 1 shows their VOLUME 24 | NUMBER 10 | OCTOBER 2010 | 2743 Copyright National Strength and Conditioning Association Unauthorized reproduction of this article is prohibited.
3 1RM Estimation Based on Isometric Squat was affixed to the ankle extramalleolus. Electromyographic signals in each trial were recorded continuously after A/D TABLE 2. Reliability (ICC) of maximum force exerted conversion at 1,000 Hz. The EMG signals were amplified, by each stance of isometric squat.* band-pass filtered (.10 Hz) and converted to root mean Wide Narrow square (RMS) in every 1-second section. In addition, the muscle activity in IS was evaluated by the relative value of Parallel 0.94 0.95 RMS during 1RM squat as a standard. 90 0.96 0.96 60 0.98 0.97 One Repetition Maximum Squat 30 0.94 0.95 To unify squat posture, the 1RM test was performed with *ICC = intracorrelation coefficient. a parallel toe and a parallel squat depth (i.e., the thigh fronts were parallel to the ground). The subjects with poor flexibility could squat with a parallel condition in a wide stance of 140% width of the shoulders. After confirming that the thigh front physical characteristics. They were selected from the was parallel to the floor, a tester sent a signal to a subject. The following sports backgrounds: baseball , soccer , and 1RM test was performed according to the more convenient rugby . They performed sports training and resistance Manabe et al.s method (16). In short, when increasing weight training 24 times per week. They had been training for .2 by 2.5 kg from the load that a subject reported himself, the years, but their mean 1RM squat was 99.1 6 15.7 kg (1.53 weight that he could not lift was decided to be 1RM. Subjects times of the weight). Informed consent was obtained from all warmed up with light weight load before the measurement. subjects after giving a full explanation of the experimental The 1RM test was performed twice after sufficient rest, and study and its procedures. This study was approved by the the best data were used for the analysis. Human Rights Committee of Kanazawa University. Isometric Squat Experimental Procedure The IS was measured by a back dynamometer (YAGAMI). The subjects performed a moderate warm-up after measure- A connection chain and a shaft were installed in a wooden ment of height and weight. After affixing electrodes for platform (Figure 1). The subjects lifted a shaft on the margo a surface electromyographic (EMG) measurement, they superior scapulae of shoulders. The direction of the toes was performed 1RM squat and IS. The order of both measure- parallel. The degree of knee flexion (squat depth) and stance ments was random. width were prescribed. Four patterns of knee flexion degree To measure action potential of the agonist during both (30, 60, 90, and parallel) were selected in reference to squats, we adopted an EMG measure (SYNA ACT MT11) previous studies (20,28). The stance width was either wide made in NEC SANEISYA. As test muscles, gastrocnemius, (140% width of the shoulders) or narrow (5-cm width), based vastus lateralis, rectus femoris, adductor longus, biceps on the reports of Steven and Donald (23) and Escamilla and femoris, gluteus maximus, gluteus medius, and erector spinae Zheng (7). muscles were selected in reference to previous studies The hip joint angle was prescribed at 60. The subject lifted (13,20,23) that examined muscle activity during squatting. the shaft that was installed to the back dynamometer on his For a bipolar lead, surface electrodes were affixed around shoulders after taking the measurement posture and performed the muscle belly of each muscle with about 50-mm space IS (Figure 2). We regarded the maximum value shown by the between the electrodes after shaving the skin surface, back dynamometer as the IS value on this occasion. The subject abrading, and cleaning with alcohol. The ground electrode performed IS twice with each movement form, and the mean TABLE 3. Summary of 2-way ANOVA on the differences of exerted maximum force by various conditions.* Two-way Post hoc, Bonferroni 30 60 90 Parallel ANOVA squat depth Stance Wide 0.95 6 0.13 0.87 6 0.13 0.76 6 0.12 0.70 6 0.08 F1 8.34 Par, 90 , 60 , 30 W.N Narrow 0.84 6 0.15 0.79 6 0.14 0.70 6 0.13 0.68 6 0.13 F2 45.77 F3 2.29 *F1 = stance; F2 = squat depth; F3 = interaction; W = wide; N = narrow; Par = parallel; ANOVA = analysis of variance. Values show relative values of isometric squat for 1RM squat. p # 0.05 the TM 2744 Journal of Strength and Conditioning Research Copyright National Strength and Conditioning Association Unauthorized reproduction of this article is prohibited.
4 TABLE 4. Summary of 2-way ANOVA on the difference of muscle activity RMS.* Post hoc, Two-way Bonferroni 30 60 90 Parallel ANOVA Squat depth Stance Gastrocnemius Wide 1.34 6 0.71 1.04 6 0.44 0.91 6 0.30 0.84 6 0.27 F1 5.05 ns W.N Narrow 1.07 6 0.51 1.00 6 0.44 0.74 6 0.21 0.76 6 0.23 F2 6.96 F3 1.56 Vastus Wide 0.22 6 0.09 0.49 6 0.15 0.62 6 0.14 0.69 6 0.15 F1 10.66 W, N: Par, Par, 90, lateralis 90 . 60 . 30 60: W . N Narrow 0.21 6 0.10 0.40 6 0.16 0.56 6 0.11 0.57 6 0.14 F2 72.55 F3 3.27 Rectus Wide 0.11 6 0.06 0.28 6 0.11 0.46 6 0.17 0.58 6 0.13 F1 10.53 W, N: Par, Par, 60: femoris 90 . 60 . 30 W.N Narrow 0.12 6 0.06 0.21 6 0.09 0.39 6 0.11 0.45 6 0.15 F2 74.23 F3 3.56 Adductor Wide 0.31 6 0.20 0.50 6 0.14 0.75 6 0.17 0.91 6 0.17 F1 1.15 Par . 90 . ns longus 60 . 30 Narrow 0.30 6 0.14 0.51 6 0.17 0.84 6 0.23 0.95 6 0.28 F2 54.53 F3 0.67 the Biceps Wide 0.87 6 0.39 1.05 6 0.44 0.95 6 0.43 0.80 6 0.35 F1 0.06 N: 60 . 90 30, ns femoris 60, 90 . Par Narrow 1.09 6 0.56 1.13 6 0.59 0.84 6 0.45 0.66 6 0.38 F2 7.46 F3 5.61 Gluteus Wide 0.61 6 0.37 0.86 6 0.30 0.95 6 0.34 0.78 6 0.25 F1 5.17 60, 90 . 30 W.N maximus Narrow 0.54 6 0.38 0.75 6 0.33 0.76 6 0.31 0.70 6 0.39 F2 7.68 F3 0.58 Gluteus Wide 0.78 6 0.42 0.85 6 0.41 0.74 6 0.41 0.62 6 0.41 F1 1.38 ns ns medius Narrow 0.65 6 0.48 0.79 6 0.49 0.66 6 0.52 0.57 6 0.55 F2 2.40 F3 0.14 Erector spinae Wide 0.73 6 0.24 0.85 6 0.22 0.94 6 0.32 0.95 6 0.22 F1 6.62 ns W.N muscles Narrow 0.72 6 0.26 0.75 6 0.16 0.78 6 0.15 0.80 6 0.18 F2 4.76 F3 1.51 *ANOVA = analysis of variance; RMS = root mean square; F1 = stance; F2 = squat depth; F3 = interaction; W = wide; N = narrow; Par = parallel; ns = nonsignificant. p # 0.05 Journal of Strength and Conditioning Research TM VOLUME 24 | NUMBER 10 | OCTOBER 2010 | 2745 | www.nsca-jscr.org Copyright National Strength and Conditioning Association Unauthorized reproduction of this article is prohibited.
5 1RM Estimation Based on Isometric Squat TABLE 5. Correlations between maximum force exerted in isometric squat and 1RM squat. Wide Narrow Parallel 0.73* 0.29 90 0.52* 0.34 60 0.56* 0.39 30 0.66* 0.30 *p # 0.05. Figure 3. Correlations between isometric squat and 1RM squats for maximum force in wide stance and parallel conditions. value was adopted. The measurement order of each movement form was random, and the rest between trials was 3 minutes. Instructions such as Keep the same posture and Do not incline the whole body were given to subjects. increasing knee flexion. On the other hand, the muscle activity of the biceps femoris increased with decreasing squat Statistical Analysis depth. The reliability of measurement values exerted by various Table 5 shows correlations between maximum force squat tests was examined by intracorrelation coefficient exerted in IS and 1RM squats. All knee flexion degrees of (ICC). Two-way analysis of variance (ANOVA;stance width IS showed significant and moderate correlations (r = 0.52 and squat depth) was used to reveal the mean difference of 0.73) with 1RM squat in the wide stance but not in the maximum force and muscle activity during IS with each narrow stance. Figure 3 shows the correlations between IS movement form. The post hoc comparisons were made using and 1RM squats for maximum force in wide stance and Bonferronis method, which adjusts the level of significance a parallel conditions. The person with a high value in IS tended by comparison number. The relationships between 1RM to have higher 1RM. A regression equation to estimate squat and IS for maximum force were examined using a 1RM squat value was calculated from the IS value, Y = Pearsons correlation coefficient. Statistical significance was 0.992X + 30.3 (Y: 1RM, X: IS). The standard error of the set at p # 0.05. estimation was 11.19 kg. RESULTS DISCUSSION Table 2 shows the reliability (ICC) of maximum force exerted by The squat is one of the most popular and important exercises each movement form of IS. All ICCs were .0.90. Table 3 shows for developing leg strength and power and has been the results of 2 factor ANOVA on the difference of the commonly included in strength training and conditioning maximum force exerted by squatting with each movement or rehabilitation programs (1,26). The squat can stimulate form. There was no significant interaction and a significant main various muscles by changing movement form and direction effect was found in stance width and knee flexure degree. Post (7,13,18,20,22,23,27). However, there are few reports of the hoc comparisons showed that maximum force in the wide influence of movement form on maximum force and muscle stance was significantly larger than that in the narrow stance. As activity during IS. Hence, we examined the difference of the for knee flexure degree, there was no significant difference above measurements in both conditions of stance width and between exerted forces at the parallel and 90 positions, but the squat depth. force was significantly larger with decreasing knee flexion Maximum force during IS was significantly larger in the (parallel, 90 , 60 , 30). wide stance than in the narrow stance. Steven and Donald Table 4 shows the results of 2 factor ANOVA on the (23) reported that muscle activity of the adductor longus and difference of muscle activity RMS exerted by IS with each gluteus maximus was significantly larger in the wide stance movement form. There were significant differences in than in the normal and narrow stances. Also in this study, the gastrocnemius, vastus lateralis, rectus femoris, gluteus wide stance showed larger muscle activities than the narrow maximus, and erector spinae muscles, and the wide stance stance in gastrocnemius, vastus lateralis, rectus femoris, showed a higher value than the narrow stance. A marked gluteus maximus, and erector spinae muscles. In particular, difference was found particularly in the vastus lateralis and because marked differences were found in the vastus lateralis rectus femoris. In gastrocnemius, vastus lateralis, rectus and the rectus femoris, an agonist muscle of knee extension, it femoris, adductor longus, gluteus maximus, and erector is inferred that the wide stance has a larger maximum force spinae muscles, muscle activity tended to increase with than the narrow stance. the TM 2746 Journal of Strength and Conditioning Research Copyright National Strength and Conditioning Association Unauthorized reproduction of this article is prohibited.
6 the TM Journal of Strength and Conditioning Research | www.nsca-jscr.org In addition, the maximum force tended to increase with estimate the squat ability in a similar manner to an isometric depthless knee flexion degree. This can be explained by the rack. relationship between joint angle and torque. All body Second, there may be a difference of operating character- movements including a straight one take place by means of istics between the static IS and the 1RM squat that can use rotation of joints, and exerted muscular strength appears as countermovement. Because the present subjects performed torque. Therefore, the amount of torque that can be exerted weight training regularly, they lifted heavier barbells skillfully by a given body joint varies considerably throughout the using a countermovement called cheat (movement by motion range of the joint. This may be explained by the which the muscle is expanded oppositely immediately before relationship of force vs. muscle length and the ever-changing the beginning of agonist muscle shortening). A rapid eccentric leverage brought about by the dynamic geometry of the muscle action stimulates the stretch reflex and builds up the muscles, tendons, and internal joint structure. Ichinose et al. elastic energy, which increases the force produced during the (12) examined the relationship between muscle fascicle subsequent concentric action. Such a movement is called length and tension in the vastus lateralis and reported that the stretch-shortening cycle (SSC) (15). The use of SSC produces tension differs with changing joint angle and the tension greater muscle power output within a short time than that shows the highest value at the 70 knee joint. from a pure concentric contraction (14,19). Manabe et al. (17) Second, it is possible that the performance of the agonist examined the influence of countermovement on muscle muscle varies as the squat posture changes. Yamashita (29) activity and joint torque and reported that a squat with performed EMG analysis upon standing from a squat position countermovement shows high muscle activity and joint and reported that muscle activity of the biceps femoris and the torque. At the time of the 1RM squat of this study, we did not rectus femoris changed during the first half (squat depth is limit use of countermovement. Therefore, it is inferred that deep) and the second half (squat depth is shallow) of the the 1RM squat showed a higher value in muscle activity and movement. In short, the rectus femoris was active in the first maximum force than the IS. half, and the biceps femoris was active in the second half. In In the present study, the maximum force of IS in wide addition, Jensen and Ebben. (13) examined the relationship stance and parallel depth showed a significant and high between squat depth and muscle activity of the biceps femoris correlation (r = 0.73) with the 1RM squat. Performing IS with and reported that although little muscle activity was found the same deep posture of the 1RM squat is important for during lifting in either squat depth, it increased when lowering the estimation of 1RM. In conclusion, although maximum from full extension of the knee to 60. force is influenced by stance width and squat depth, IS In this study, when squat depth increased, the activity of measurement values with wide stance and parallel depth may gastrocnemius, vastus lateralis, rectus femoris, adductor be useful for the estimation of 1RM squat. longus, gluteus maximus, and erector spinae muscles in- creased. The main function of erector spinae muscles is PRACTICAL APPLICATIONS postural maintenance with trunk extension. When squat depth increased, increasing force was required to bend the Simple linear regression analysis revealed a relationship of Y = trunk forward during lifting; thus, muscle activity may 0.992X + 30.3 (Y: 1RM, X: IS). This suggests that the IS using increase. Additionally, it is possible that the vastus lateralis, a back dynamometer may become an effective index for an agonist of knee extension, and the gluteus maximus, an predicting 1RM squat. However, the standard error of an agonist of hip extension, act independently of each other with estimate provided by the regression equation was quite large, increasing squat depth. On the other hand, the muscle activity 11.19 kg, in subjects of only moderate squat ability (about 1.5 of the biceps femoris increased with decreased squat depth. times body weight). Therefore, it is hypothesized that the When evaluating the muscle activity in the IS with a relative standard error will increase when applied to subjects without value based on the RMS at the time of the 1RM squat, all weight training experience. In addition, it has been reported muscles were ,1.0. In other words, muscle activity in the that the maintenance of posture during IS using a back- IS tended to be less than that in the 1RM measurement. dynamometer is difficult. From a practical application Similarly maximum force tended to be ,1RM. Blazevich et al. standpoint, a device that stabilizes posture will be needed (3) reported that the IS using the isometric rack was about in the future. 1.4 times maximum force at 1RM squat. This was the same isometric condition, but the results were markedly different. This may be because of a difference of the experimental REFERENCES device. When measuring the squat ability using the back 1. Abelbeck, KG. 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