The purposes of this study were to examine the effect of ballistic concentric-only half-squats (COHS) on subsequent squat-jump (SJ) performances at various rest intervals and to examine the relationships between changes in SJ performance and bilateral symmetry at peak performance. Thirteen resistance-trained men performed an SJ immediately and every minute up to 10 min on dual force plates after 2 ballistic COHS repetitions at 90% of their 1-repetition-maximum COHS. SJ peak force, peak power, net impulse, and rate of force development (RFD) were compared using a series of 1-way repeated-measures ANOVAs. The percent change in performance at which peak performance occurred for each variable was correlated with the symmetry index scores at the corresponding time point using Pearson correlation coefficients. Statistical differences in peak power (P = .031) existed between rest intervals; however, no statistically significant pairwise comparisons were present (P > .05). No statistical differences in peak force (P = .201), net impulse (P = .064), and RFD (P = .477) were present between rest intervals. The relationships between changes in SJ performance and bilateral symmetry after the rest interval that produced the greatest performance for peak force (r = .300, P = .319), peak power (r = –.041, P = .894), net impulse (r = –.028, P = .927), and RFD (r = –.434, P = .138) were not statistically significant. Ballistic COHS may enhance SJ performance; however, the changes in performance were not related to bilateral symmetry.
Timothy J. Suchomel, Kimitake Sato, Brad H. DeWeese, William P. Ebben and Michael H. Stone
Diane Austrin Klein, William J. Stone, Wayne T. Phillips, Jaime Gangi and Sarah Hartman
The impact of proprioceptive neuromuscular facilitation (PNF) on physical function in assisted-living older adults (73-94 years old) was studied. A 5-week pretraining period consisting of weekly visits by trainers to participants preceded a 10-week training period of warm-up, PNF exercises, and cool-down. Training progressed from 1 set of 3 repetitions to 3 sets of 3 repetitions. Assessments were conducted at baseline (T1), postpretraining (T2), and posttraining (T3). Eleven of 14 volunteer participants completed the study. Physical function was assessed by range of motion (ROM), isometric strength, and balance and mobility measures. Repeated-measures ANOVA identified 6 measures (sit-to-stand, shoulder- and ankle-flexion ROM, and hip-extension, ankle-flexion, and ankle-extension strength) with statistically significant differences. With the exception of hip-extension strength, these measures were statistically significant from T2 to T3 in post hoc univariate tests. Results indicate that PNF flexibility training can improve ROM, isometric strength, and selected physical-function tasks in assisted-living older adults.
Gary S. Krahenbuhl, Robert P. Pangrazi, William J. Stone, Don W. Morgan and Tracy Williams
Untrained 6- to 8-year-old children (N = 80) served as subjects in a cross sectional study of the fractional utilization of maximal aerobic power during submaximal running. Using the open-circuit method, the absolute oxygen demands of submaximal running were found to increase with age. When expressed relative to body weight, oxygen demands of submaximal running showed no statistically significant changes over the 3-year span. VO2max increased 36.2%, which was proportionally greater than the percentage increase for either body weight (28.4%) or the absolute oxygen demands of submaximal running (22.9%). Thus, during the span of years studied there was a significant reduction in the fractional utilization of maximal aerobic power required to run at a fixed submaximal speed.
Andrew C. Fry, William J. Kraemer, Michael H. Stone, Beverly J. Warren, Jay T. Kearney, Carl M. Maresh, Cheryl A. Weseman and Steven J. Fleck
To examine the effects of 1 week of high volume weightlifting and amino acid supplementation, 28 elite junior male weightlifting received either amino acid (protein) or lactose (placebo) capsules using double-blind procedures. weightlifting test sessions were performed before and after 7 days of high volume training sessions. Serum concentrations of testosterone (Tes), cortisol (Cort), and growth hormone (GH) as well as whole blood iactate (HLa) were determined from blood draws. Lifting performance was not altered for either group after training, although vertical jump performance decreased for both groups. Both tests elicited significantly elevated exercise-induced hormonal and HLa concentrations. Significant decreases in postexercise hormonal and HLa concentrations from Test 1 to Test 2 were observed for both groups. Tes concentrations at 7 a.m. and preexercise decreased for both groups from Test 1 to Test 2, while the placebo group exhibited a decreased 7 a.m. Tes/ Cort. These data suggest that amino acid supplementation does not influence resting or exercise-induced hormonal responses to 1 week of high volume weight training, but endocrine responses did suggest an impending overtraining syndrome.