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The maximal dynamic output (MDO) hypothesis is a newly proposed concept, which suggests that the muscular system of the lower limbs is designed to produce maximal power output when performing countermovement vertical jumping (CMJ) at body mass as opposed to other loading conditions. However, it is unclear if the MDO concept can be applied to individuals with different levels of maximal strength. The purpose of this investigation was to determine if subjects, who have distinct differences in maximal strength, maximize CMJ power at body mass. Fourteen male strength-power trained subjects (squat 1 repetition maximum (1RM)-to-body mass ratio = 1.96 [+ or -] 0.24) and 6 untrained male subjects (squat 1RM-to-body mass ratio = 0.94 [+ or -] 0.18) completed CMJs with loads that were less than, equal to, and greater than body mass. Loads less than body mass were accomplished with a custom-designed unloading apparatus, and loads greater than body mass were accomplished with a barbell and weights. In both groups, mean values for CMJ peak and mean power were greatest during the body mass jump. Power outputs at body mass were significantly different (p [less than or equal to] 0.05) than power outputs at various conditions of loading and unloading. These data support the MDO hypothesis and its application to individuals with significantly different 1RM-to-body mass ratios. Additionally, these data further support the idea that body mass CMJs are a theoretically sound way to train for power because of the maximal power outputs that are produced during this condition. KEY WORDS strength, power, vertical jump, unloading

J Strength Cond Res 24(1): 190-194, 2010--The purpose of this investigation was to compare kinetic and kinematic variables between squats performed with and without elastic bands equalized for total work. Ten recreationally weight trained males completed 1 set of 5 squats without (Wht) and with (Band) elastic bands as resistance. Squats were completed while standing on a force platform with bar displacement measured using 2 potentiometers. Electromyography (EMG) was obtained from the vastus lateralis. Average force-time, velocity-time, power-time, and EMG-time graphs were generated and statistically analyzed for mean differences in values between the 2 conditions during the eccentric and concentric phases. The Band condition resulted in significantly higher forces in comparison to the Wht condition during the first 25% of the eccentric phase and the last 10% of the concentric phase (p [less than or equal to] 0.05). However, the Wht condition resulted in significantly higher forces during the last 5% of the eccentric phase and the first 5% of the concentric phase in comparison to the Band condition. The Band condition resulted in significantly higher power and velocity values during the first portion of the eccentric phase and the latter portion of the concentric phase. Vastus lateralis muscle activity during the Band condition was significantly greater during the first portion of the eccentric phase and latter portion of the concentric phase as well. This investigation indicates that squats equalized for total work with and without elastic bands significantly alter the force-time, power-time, velocity-time, and EMG-time curves associated with the movements. Specifically, elastic bands seem to increase force, power, and muscle activity during the early portions of the eccentric phase and latter portions of the concentric phase. KEY WORDS force, power, velocity, EMG

J Strength Cond Res 24(1): 184-189, 2010--The purpose of the current investigation was to assess the effect of an acute bout of whole body vibration (WBV) exercise on muscle force output and motor neuron excitability. Nineteen recreationally trained college-aged males were randomly assigned to a WBV (n = 10) or a sham (S, n = 9) group. The WBV group completed a series of static, body weight squats on a vibrating platform at 30 Hz and an amplitude of ~3.5 mm (vertical), whereas the S group performed the same series of exercises but without vibration. Measurements were performed before (Pre) and then immediately post-exercise (Imm Post), 8 minutes post-exercise (8-Min Post), or 16 minutes post-exercise (16-Min Post) during 3 different testing sessions. The measurements involved a ballistic isometric maximum voluntary contraction (MVC) of the triceps surae muscle complex and electrical stimulation of the tibial nerve for assessment of motor neuron excitability by analyzing H-reflex and M-wave responses ([H.sub.max]/[M.sub.max] ratio). Electromyography was also obtained from the triceps surae muscle complex during the MVCs. The WBV group significantly (p [less than or equal to] 0.05) increased peak force at Imm Post (9.4%) and 8-Min Post (10.4%). No significant change in peak force was observed in the S group. No significant changes were observed in either group for average integrated EMG, [H.sub.max]/[M.sub.max] ratio, or rate of force development at Imm Post, 8-Min Post, or 16-Min Post. The results from this investigation indicate that an acute bout of static, body weight squat exercises, combined with WBV, increases muscle force output up to 8 minutes post-exercise. However, this increase in muscle force is not accompanied by a significant increase in motor neuron excitability or muscle activation. Thus, it is plausible to use WBV as a method for acute increase in muscle force output for athletes immediately before competition. KEY WORDS potentiation, electromyography, H reflex, M wave

The purpose of this investigation was to examine the relationship between maximal squat strength and sprinting times. Seventeen Division I-AA male football athletes (height = 1.78 [+ or -] 0.04 m, body mass [BM] = 85.9 [+ or -] 8.8 kg, body mass index [BMI] = 27.0 [+ or -] 2.6 kg/[m.sup.2], 1 repetition maximum [1RM] = 166.5 [+ or -] 34.1 kg, 1RM/BM = 1.94 [+ or -] 0.33) participated in this investigation. Height, weight, and squat strength (1RM) were assessed on day 1. Within 1 week, 5, 10, and 40 yard sprint times were assessed. Squats were performed to a 70[degrees] knee angle and values expressed relative to each subject's BM. Sprints were performed on a standard outdoor track surface with timing gates placed at the previously mentioned distances. Statistically significant (p [less than or equal to] 0.05) correlations were found between squat 1 RM/BM and 40 yard sprint times (r = -0.605, p = 0.010, power = 0.747) and 10 yard sprint times (r = -0.544, p = 0.024, power = 0.626). The correlation approached significance between 5 yard sprint times and 1RM/BM (r = -0.4502, p = 0.0698, power = 0.4421). Subjects were then divided into those above 1RM/BM of 2.10 and below 1RM/BM of 1.90. Subjects with a 1RM/BM above 2.10 had statistically significantly lower sprint times at 10 and 40 yards in comparison with those subjects with a 1RM/BM ratio below 1.90. This investigation provides additional evidence of the possible importance of maximal squat strength relative to BM concerning sprinting capabilities in competitive athletes. KEY WORDS power, running, football, athletes

The purpose of this study was to determine whether there is a linear relationship between the squat and a variety of quadriceps resistance training exercises for the purpose of creating prediction equations for the determination of quadriceps exercise loads based on the squat load. Six-repetition maximums (RMs) of the squat, as well as four common resistance training exercises that activate the quadriceps including the deadlift, lunge, step-up, and leg extension, were determined for each subject. Subjects included 21 college students. Data were evaluated using linear regression analysis to predict quadriceps exercise loads from 6RM squat data and were cross-validated with the prediction of sum of squares statistic. Analysis of the data revealed that the squat is a significant predictor of loads for the dead lift ([R.sup.2] = 0.81, standard error of the estimate [SEE] = 12.50 kg), lunge ([R.sup.2] = 0.62, SEE = 12.57 kg), step-up ([R.sup.2] = 0.71, SEE = 9.58 kg), and leg extension ([R.sup.2] = 0.67, SEE = 10.26 kg) exercises. Based on the analysis of the data, the following 6RM prediction equations were devised for each exercise: (a) deadlift load = squat load (0.83) + 14.92 kg, (b) lunge load = squat load (0.52) + 14.82 kg, (c) step-up load = squat load (0.50) + 3.32 kg, and (d) leg extension load = squat load (0.48) + 9.58 kg. Results from testing core exercises such as the squat can provide useful data for the assignment of loads for other exercises. KEY WORDS strength, testing, load, program design

The purpose of this investigation was to determine the relationship between relative net vertical impulse and jump height in a countermovement jump and static jump performed to varying squat depths. Ten college-aged males with 2 years of jumping experience participated in this investigation (age: 23.3 ± 1.5 years; height: 176.7 ± 4.5 cm; body mass: 84.4 ± 10.1 kg). Subjects performed a series of static jumps and countermovement jumps in a randomized fashion to a depth of 0.15, 0.30, 0.45, 0.60, and 0.75 m and a self-selected depth (static jump depth = 0.38 ± 0.08 m, countermovement jump depth = 0.49 ± 0.06 m). During the concentric phase of each jump, peak force, peak velocity, peak power, jump height, and net vertical impulse were recorded and analyzed. Net vertical impulse was divided by body mass to produce relative net vertical impulse. Increasing squat depth corresponded to a decrease in peak force and an increase in jump height and relative net vertical impulse for both static jump and countermovement jump. Across all depths, relative net vertical impulse was statistically significantly correlated to jump height in the static jump (r = .9337, p < .0001, power = 1.000) and countermovement jump (r = .925, p < .0001, power = 1.000). Across all depths, peak force was negatively correlated to jump height in the static jump (r = -0.3947, p = .0018, power = 0.8831) and countermovement jump (r = -0.4080, p = .0012, power = 0.9050). These results indicate that relative net vertical impulse can be used to assess vertical jump performance, regardless of initial squat depth, and that peak force may not be the best measure to assess vertical jump performance. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this investigation was to determine the effect of stable and unstable conditions on one repetition maximum strength and muscle activity during dynamic squatting using absolute and relative loading. Methods: Ten recreationally weight-trained males participated in this study (age = 24.1 ± 2.0 y, height = 178.0 ± 5.6 cm, body mass = 83.7 ± 13.4 kg, 1RM/body mass = 1.53 ± 0.31), which involved two laboratory sessions separated by 1 wk. Linear position transducers were used to track bar displacement while subjects stood on a force plate for all trials. Vastus lateralis (VL), biceps femoris (BF) and erector spinae (L1) muscle activity (average integrated EMG [IEMG]) was also recorded during all trials. During the first session subjects complete a one repetition maximum test in a stable dynamic squat (S1RM = 128.0 ± 31.4 kg) and an unstable dynamic squat (U1RM = 83.8 ± 17.3 kg) in a randomized order with a 30-min rest period between conditions. The second session consisted of the performance of three trials each for 12 different conditions (unstable and stable squats using three different absolute loads [six conditions] and unstable and stable squats using three different relative loads [six conditions]). Results: Results revealed a statistically significant difference between S1RM and U1RM values (P ≤ .05). The stable trials resulted in the same or a significantly higher value for VL, BF and L1 muscle activity in comparison with the unstable trials for all twelve conditions. Conclusions: Unstable squatting is of equal or less (depending on the loading condition) benefit to improving or maximizing muscle activity during resistance exercise. [ABSTRACT FROM AUTHOR]

The article presents the results of a study which investigated kinetic and kinematic variables during squat exercises performed with and without elastic bands. Force-time, velocity-time, power-time and electromyography (EMG)-time were analyzed for weight trained male participants. It was found that elastic bands influenced force, power and muscle activity during eccentric and concentric phases.