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.
Tyler J. Kirby, Jeffrey M. McBride, Tracie L. Haines and Andrea M. Dayne
Jeffrey M. McBride, Tony R. Larkin, Andrea M. Dayne, Tracie L. Haines and Tyler J. Kirby
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.
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 frst 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 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.
Unstable squatting is of equal or less (depending on the loading condition) benefit to improving or maximizing muscle activity during resistance exercise.