The purpose of this study was to determine if a power exercise would lead to greater postactivation potentiation (PAP) than a strength exercise, if a 4-or 5-minute rest interval led to greater PAP, the extent to which PAP was an individual phenomenon, and the effect of PAP on the ground reaction force (GRF) during a vertical jump (VJ). Subjects included 16 volleyball athletes (8 men and 8 women) from a Division I university. Participants were instructed to complete a pre-exercise countermovement jump for height. After the VJ, subjects performed 5 repetitions of either the back squat or hang clean (midthigh) with a load equal to their 5 repetition maximum (5RM). After the 5RM resistance exercise, countermovement jumps were completed at 4 or 5 minutes after the back squat or hang clean. Ground reaction force was measured using a force platform embedded in the ground, whereas VJ height was assessed using a Vertec jump apparatus. Data were analyzed using a factorial analysis of variance with repeated measures. Results revealed that there was no consistent rest interval or exercise that produced the largest increase in VJ height for all subjects, and there were no apparent differences because of gender. The condition that produced the largest increase in VJ height for each individual resulted in an average increase of 5.7% (2.72 +/- 1.21 cm; p < 0.001). There was no significant difference (p > 0.05) in peak GRF, and no significant correlation (r = -0.110, p = 0.707) between the increase in VJ height and increase in peak GRF. Results suggest that individually determining complex training variables will increase VJ height, thus acutely enhancing athletic performance.

In an attempt to mimic everyday activities that are performed in 3-dimensional environments, exercise programs have been designed to integrate training of the trunk muscles with training of the extremities. Many believe that the most effective way to recruit the core stabilizing muscles is to execute traditional exercise movements on unstable surfaces. However, physical activity is rarely performed with a stable load on an unstable surface; usually, the surface is stable, and the external resistance is not. The purpose of this study was to evaluate muscle activity of the prime movers and core stabilizers while lifting stable and unstable loads on stable and unstable surfaces during the seated overhead shoulder press exercise. Thirty resistance-trained subjects performed the shoulder press exercise for 3 sets of 3 repetitions under 2 load (barbell and dumbbell) and 2 surface (exercise bench and Swiss ball) conditions at a 10 repetition maximum relative intensity. Surface electromyography (EMG) measured muscle activity for 8 muscles (anterior deltoid, middle deltoid, trapezius, triceps brachii, rectus abdominis, external obliques, and upper and lower erector spinae). The average root mean square of the EMG signal was calculated for each condition. The results showed that as the instability of the exercise condition increased, the external load decreased. Triceps activation increased with external resistance, where the barbell/bench condition had the greatest EMG activation and the dumbbell/Swiss ball condition had the least. The upper erector spinae had greater muscle activation when performing the barbell presses on the Swiss ball vs. the bench. The findings provide little support for training with a lighter load using unstable loads or unstable surfaces.

Purpose-Squatting activities may be used, within exercise programs, to preserve physical function in older adults. This study characterized the lower-extremity peak joint angles, peak moments, powers, work, impulse, and muscle recruitment patterns (electromyographic; EMG) associated with two types of squatting activities in elders.Methods-Twenty-two healthy, older adults (ages 70-85) performed three trials each of: 1) a squat to a self-selected depth (normal squat; SQ) and 2) a squat onto a chair with a standardized height of 43.8 cm (chair squat; CSQ). Descending and ascending phase joint kinematics and kinetics were obtained using a motion analysis system and inverse dynamics techniques. Results were averaged across the three trials. A 2 × 2 (activity × phase) ANOVA with repeated measures was used to examine the biomechanical differences among the two activities and phases. EMG temporal characteristics were qualitatively examined.Results-CSQ generated greater hip flexion angles, peak moments, power, and work, whereas SQ generated greater knee and ankle flexion angles, peak moments, power, and work. SQ generated a greater knee extensor impulse, a greater plantar flexor impulse and a greater total support impulse. The EMG temporal patterns were consistent with the kinetic data. Conclusions-The results suggest that, with older adults, CSQ places greater demand on the hip extensors, whereas SQ places greater demand on the knee extensors and ankle plantar flexors. Clinicians may use these discriminate findings to more effectively target specific lower-extremity muscle groups when prescribing exercise for older adults. Keywords AGING; BIOMECHANICS; JOINT MOMENT; JOINT POWER; EMG; CHAIR SQUAT; BOX SQUATResistance exercise prescription is a diverse science used to improve sport performance, rehabilitate injury, and preserve functional independence in older adults. Despite its branching applicability, all resistance exercise prescriptions require a fundamental analysis, termed needs analysis. Needs analysis is the process whereby clinicians, coaches, and NIH Public Access Author ManuscriptMed Sci Sports Exerc. Author manuscript; available in PMC 2012 October 17. rehabilitation specialists analyze the biomechanical requirements of an activity to select resistance exercises with similar motor recruitment patterns. Thus, appropriate resistance exercise prescription requires an analysis of both the activity to be improved, restored, or preserved and the exercises that may be used in these endeavors.The preservation of physical independence is a growing concern within our society, receiving attention from geriatric clinicians, educators, researchers, and exercise specialists. Walking, sitting and rising from a chair, and ascending and descending stairs are important determinants of independence; consequently, researchers are using biomechanical analyses to better characterize these activities. Gait has received comprehensive biomechanical evaluation (30), and although not as consolidated, there is considerable biom...

Bilateral movements are common in human movement, both as exercises and as daily activities. Because the movement patterns are similar, it is often assumed that there are no bilateral differences (BDs; differences between the left and right sides) in the joint torques that are producing these movements. The aim of this investigation was to test the assumption that the joint torques are equal between the left and right lower extremities by quantifying BDs during the barbell squat. Eighteen recreationally trained men (n = 9) and women (n = 9) completed 3 sets of 3 repetitions of the squat exercise, under 4 loading conditions: 25, 50, 75, and 100% of their 3 repetition maximum, while instrumented for biomechanical analysis. The average net joint moment (ANJM) and maximum flexion angle (MFA) for the hip, knee, and ankle as well as the average vertical ground reaction force (AVGRF) and the average distance from the ankle joint center to the center of pressure (ADCOP) were calculated. Group mean and individual data were analyzed (alpha = 0.05). At each joint, there was a significant main effect for side and load, no main effect for gender, with few significant interactions. The hip ANJM was 12.4% larger on the left side, the knee ANJM was 13.2% larger on the right side, and the ankle ANJM was 16.8% larger on the left side. Differences in MFAs between sides were less than 2 degrees for all 3 joints (all p > 0.20 except for the knee at 75% [p = 0.024] and 100% [p = 0.025]), but the AVGRF and the ADCOP were 6% and 11% larger on the left side. Few subjects exhibited the pattern identified with the group mean data, and no subject exhibited nonsignificant BDs for all 3 joints. These findings suggest that joint torques should not be assumed to be equal during the squat and that few individual subjects follow the pattern exhibited by group mean data.

The purpose of this investigation was to determine if increases in external resistance during a squat movement would be controlled by proportionally scaling the net joint moment work or average net joint moment (NJM) at the hip, knee, and ankle. Eighteen experienced subjects performed 3 sets of 3 repetitions each of a squat movement using resistances of 25, 50, 75, and 100% of their 3-repetition maximum, while instrumented for biomechanical analyses. Standard inverse dynamics techniques and numerical integration were used to calculate the NJM work and average NJM of each joint. A combination of single-subject and group mean statistical analyses indicated that the neither the NJM work nor average NJM increased proportionately in response to increases in external loading. Results suggest a complex control strategy in which the hip was the dominant contributor, increased linearly with the external load, and had low variability. The knee and ankle contributions were neither as great nor as linear, and were highly variable, suggesting that they were influenced by more than just the external load. The disproportionate response of each joint to varying external resistances suggests that controlling the force output of multijoint chains requires further study and modifications to existing motor control theories.