Effects of After-School Strength Training on Adolescents' Muscular Strength Wenhao Liu 1, Shawn L. S. Bean 2, Traci D. Zillifro 1 and Jeffrey Smith 1 ; (1) Slippery Rock University, Slippery Rock, PA; (2) Cranberry Junior Senior High School, Seneca, PA Abstract Purpose: This study investigated effect of an after-school strength training program on improving muscular strength and endurance among high school adolescents. Method: Sixteen high school students forming an intervention group participated in an eight-week after-school strength training program containing three 45-minute sessions per week. In each session the participant went through ten muscle-strengthening exercises/stations to perform three sets of ten repetitions at each station with 50-60% of the individual's one RM in the first three weeks of the intervention, 60-70% in the next three weeks, and 70-80% in the last two weeks. Another 16 students from the same school made up a control group without receiving any intervention. Two groups had similar ages (15.63±1.03 vs ±1.13) and contained 11 males, were all enrolled in PE classes meeting twice/week, and received a pretest (before intervention) and posttest (after intervention) of push-ups and curl-ups. Results: One-way ANCOVA indicated significant differences (p <.05) in adjusted means in the posttest scores in favor of the intervention group. The posttest scores of push-ups were 22.09±8.08 for the intervention group vs ±6.66 for the control group, and curl-ups were 68.14±11.57 vs ± Conclusions: The after-school strength training program is effective in increasing high school students' muscular strength and endurance. Introduction Childhood obesity prevalence has more than tripled in the past thirty years (CDC, 2010), and the obesity issue among school aged students in the US is a serious national concern. Research indicates that obese youth are more likely to become overweight or obese adults, and therefore more at risk in associated adult health problems such as heart disease, type 2 diabetes, stroke, several types of cancer, and osteoarthritis. Due to the limited PE class time and high prevalence of obesity Method Sixteen high school students constituting an intervention group participated in an eight-week after-school strength training program, which contained three 45-minute sessions per week. The circuit-strength training consisted of ten stations or exercises. In each session the participant went through the ten muscle-strengthening exercises/stations to perform three sets of ten repetitions at each station. In the first three weeks of the intervention, the intervention participant used weights equivalent to 50-60% of the individual's one repetition maximum. During weeks of four through six the weights increased to 60-70% of the repetition maximum. In the last two weeks weights of 70-80% of the repetition maximum were used. The change in weights was the only change that was allowed during the eight-week strength training program. Another sixteen high school students from the same school made up a control group, which did not receive any intervention. The two groups had similar ages (15.63 ± 1.03 vs ± 1.13), contained the same number of males (11 males), were all enrolled in PE classes meeting twice/week. A pretest (before intervention) and posttest (after intervention) of push- ups and curl-ups were conducted on the two groups. Results Results of one-way ANCOVA indicated significant differences in adjusted means in the posttest scores in favor of the intervention group while controlling for the pretest scores. Specifically, the posttest scores (adjusted means) of push-ups were ± 8.08 for the intervention group vs ±6.66 for the control group (p <.05), and curl-ups were ± vs ± (p <.05). Conclusions The after-school strength training program, which lasted eight weeks and met three times per week, is effective in increasing high school students' muscular strength and endurance. among children and adolescents, after-school physical activity programs have become an important supplement to PE classes in increasing students' physical activity and fitness level. This study investigated the effect of an after-school strength training program on improving muscular strength and endurance among high school adolescents. One-way ANCOVA was used to compare the posttest fitness scores of push-ups and curl-ups while controlling for the pretest scores.