Brian J. Wallace

Effects of elastic bands on force and power characteristics during the back squat exercise.

Athletes commonly use elastic bands as a training method to increase strength and performance. The purpose of this study was to investigate the effect of elastic bands on peak force (PF), peak power (PP), and peak rate of force development (RFD) during the back-squat exercise (BSE). Ten recreationally resistance-trained subjects (4 women, 6 men, mean age 21.3 ± 1.5 years) were tested for their 1 repetition maximum (1RM) in the BSE (mean 117.6 ± 48.2 kg) on a Smith machine. Testing was performed on 2 separate days, with 2 sets of 3 repetitions being performed for each condition. Testing was conducted at 60% and 85% of 1RM with and without using elastic bands. In addition, 2 elastic band loading conditions were tested (B1 and B2) at each of the 2 resistances. No bands (NB) represents where all of the resistance was acquired from free-weights. B1 represents where approximately 80% of the resistance was provided by free-weights, and approximately 20% was provided by bands. B2 represents where approximately 65% of the resistance was provided by free-weights, and approximately 35% was provided from bands. The subjects completed the BSE under each condition, whereas PF, PP, and RFD was recorded using a force platform. There was a significant (p < 0.05) increase in PF between NB-85 and B2-85 of 16%. Between B1-85 and B2-85, PF was increased significantly by 5% (p < 0.05). There was a significant (p < 0.05) increase in PP between NB-85 and B2-85 of 24%. No significant differences were observed in RFD during the 85% conditions or for any of the measured variables during the 60% conditions (p < 0.05). The results suggest that the use of elastic bands in conjunction with free weights can significantly increase PF and PP during the BSE over free-weight resistance alone under certain loading conditions. The greatest differences are observed during the higher loading conditions, with the B1-85 condition appearing to be optimal for athletic performance of the ones we tested. The strength training professional could use variable resistance training (VRT) to increase PF and PP more than the traditional BSE can. VRT could also be used to train these 2 performance characteristics together, which might be especially useful in season, when weight-room training volume can sometimes be limited.

Quantification of vertical ground reaction forces of popular bilateral plyometric exercises.

Wallace, BJ, Kernozek, TW, White, JM, Kline, DE, Wright, GA, Peng, H-T, and Huang, C-F. Quantification of vertical ground reaction forces of popular bilateral plyometric exercises. J Strength Cond Res 24(1): 207-212, 2010-The purpose of this study was to quantify the vertical ground reaction forces (VGRFs) developed during the performance of popular bilateral plyometric movements. Fourteen power-oriented track and field men of collegiate and national level randomly performed 3 trials of 9 different bilateral plyometric exercises in a single testing session. Three depth drop (DD) and 3 depth jump (DJ) conditions from 30, 60, and 90 cm heights (DD30, DD60, and DD90 and DJ30, DJ60, and DJ90) were tested, in addition to vertical jump (VJ), standing long jump (SLJ), and 2 consecutive jump (2CJ) conditions. Peak impact VGRFs were normalized to body weight. Additionally, all conditions were compared against the VJ in an intensity index. The SLJ condition resulted in a significantly higher peak VGRF than the 2CJ condition (p ≤ 0.05). 90DD, 90DJ, 60DD, and SLJ had a significantly greater peak VGRF (5.39, 4.93, 4.30, and 4.22 times body weight, respectively) than the VJ condition (3.34 times body weight). The 30DJ condition had an insignificantly smaller peak VGRF (2.78 times body weight) when compared with the VJ. Practitioners may use these findings to more effectively progress athletes in these movements based on their intensities.

A comparison between back squat exercise and vertical jump kinematics: implications for determining anterior cruciate ligament injury risk.

Wallace, BJ, Kernozek, TW, Mikat, RP, Wright, GA, Simons, SZ, and Wallace, KL. A comparison between back squat exercise and vertical jump kinematics: implications for determining anterior cruciate ligament injury risk. J Strength Cond Res 22: 1249-1258, 2008-Women are up to eight times more likely than men to suffer an anterior cruciate ligament (ACL) injury, and knee valgus is perhaps the most at-risk motion. Women have been shown to have more knee valgus than men in squatting movements and while landing. The purposes were to investigate whether a relationship exists between lower-extremity frontal plane motions in squatting and landing, whether gender differences exist, and whether squat or hip abduction strength relates to knee valgus while landing. Eleven collegiate Division III soccer players and 11 recreationally trained men were tested for maximal vertical jump height and for squat and hip abduction strength. On the second day of testing, subjects performed light (50% one repetition maximum) and heavy (85%) squat protocols and three landings from their maximal vertical jump height. Pearsons product-moment correlation coefficients and a 2 × 10 factorial analysis of variance with t-test post hoc comparisons (p ≤ 0.05) were conducted. No strong correlations were shown between any of the squat conditions (eccentric and concentric light, eccentric and concentric heavy) and landing for hip abduction or knee valgus angles. Squat strength did not correlate well with knee valgus angle during landing in men or women. However, hip abduction strength did in women (R2 = 0.51) but not men (R2 = 0.10). In hip abduction angle, the eccentric portion of the light squat, eccentric and concentric portions of the heavy squat, and vertical jump landing conditions were different between genders. In knee valgus angle, only the heavy squat conditions were significantly different. Squat strength and observing squat kinematics do not seem to be a method of identifying those at risk while landing; however, hip abduction strength may be in women.

Implications of Motor Unit Activity on Ballistic Movement

In many competitive sports the ability to develop high amounts of force quickly is paramount to success. Ballistic methods of training have been employed by strength and sport coaches as a means of improving this performance characteristic. However, a thorough understanding of the bodys responses to this type of training is necessary to adequately implement ballistic exercises into a physical training program. The scientific literature shows that the neuromuscular system behaves differently while performing ballistic movements than it does when performing movements requiring a lower velocity or rate of force development. This article aims to discuss nervous system muscle recruitment under progressive loading conditions, as well as high velocity and high rate of force development conditions acutely and chronically. It also provides programming suggestions regarding methods coaches could use to train athletes who participate in ballistic sports.

Optimum Drop Jump Height in Division III Athletes: Under 75% of Vertical Jump Height

Our purpose was to evaluate the vertical ground reaction force, impulse, moments and powers of hip, knee and ankle joints, contact time, and jump height when performing a drop jump from different drop heights based on the percentage of a performers maximum vertical jump height (MVJH). Fifteen male Division III athletes participated voluntarily. Eleven synchronized cameras and two force platforms were used to collect data. One-way repeated-measures analysis of variance tests were used to examine the differences between drop heights. The maximum hip, knee and ankle power absorption during 125%MVJH and 150%MVJH were greater than those during 75%MVJH. The impulse during landing at 100%MVJH, 125%MVJH and 150%MVJH were greater than 75%MVJH. The vertical ground reaction force during 150%MVJH was greater than 50%MVJH, 75%MVJH and 100%MVJH. Drop height below 75%MVJH had the most merits for increasing joint power output while having a lower impact force, impulse and joint power absorption. Drop height of 150%MVJH may not be desirable as a high-intensity stimulus due to the much greater impact force, increasing the risk of injury, without increasing jump height performance.