Clark B. Rians's research while affiliated with University of Virginia and other places

Twenty-nine prepubertal males (X̄ age = 8.2 ± 1.3 years) were evaluated for concentric isokinetic strength at the knee, shoulder, and elbow joints, [at the dominant (D) and nondominant (ND) sides]. At each joint, flexion (F) was compared with extension (E) at two speeds of 30°/sec (30) versus 9o°/sec (90) over each 10% of the range of motion (ROM). Reliability was estimated between identical motions at the D versus ND side. Results for X̄ work at the knee joint indicated slightly higher work output at the ND side (23.5 versus 25.0 joules for D versus ND), significantly higher work output for extension compared to flexion (19.0 versus 29.2 joules for F versus E) and for the slower compared to the faster speed (26.2 versus 21.9 joules for 30 versus 90). At the shoulder joint, extension resulted in significantly greater X̄ work compared to flexion (14.2 versus 22.0 joules for F versus E) and the slower speed was associated with significantly greater X̄ work (19.7 versus 16.7 joules for 30 versus 90). At the elbow joint, the only significant difference observed for X̄ work occurred for speed, with the faster speed resulting in greater X̄ work (10.8 versus 9.5 joules for 30 versus 90). Analysis for torque scores at each of the three joints revealed that extension resulted in greater torque than flexion, 30°/sec resulted in greater torque than 90°/sec and that peak torque scores occurred during the first 50% of ROM. Correlations to estimate reliability exceeded r = 0.70 for comparisons of torque and work scores for D versus ND. Age, height, and weight correlated r= 0.50<r<0.90 with peak torque during each of the motions. It was concluded that prepubertal males have similar patterns of concentric isokinetic strength measured at the knee, shoulder, and elbow joints compared to adults, because strength was greater during E versus F, for slower versus faster speeds, and during the initial phase of ROM.

This study examined the safety of one type of strength training for prepubescent males. Eighteen males (av erage age, 8.3 ± 1.2 years) participated in a 45 min/ session, three session/week, 14 week supervised strength training program with an attendance rate of 91.5%. Concentric work was done almost exclusively. KinCom analysis showed significant strength gain in this group (P < 0.05), while an age, sex, and activity matched control group did not gain strength. Safety was evaluated by injury surveillance, blood pressure and heart rate monitoring, scintigraphy, and creatine phosphokinase measurement. Effects on growth and development, flexibility, and motor perform ance were also investigated, as these are factors with an impact on sports injury occurrence. Results showed that in the short term, supervised concentric strength training results in a low injury rate and does not adversely affect bone, muscle, or epi physes ; nor does it adversely affect growth, develop ment, flexibility, or motor performance. As the safety question is multifaceted, this should not lead to the conclusion that strength training for prepubescents is uniformly safe. Further research is needed.

In order to examine the effectiveness and safety of hydraulic resistance strength training in young males, 26 pre-pubertal males (mean age = 8.2 +/- 1.3 yr) completed a 14-wk strength training study. Subjects were evaluated before and after the 14-wk experimental period for pubertal state (Tanner's sexual maturity rating, serum testosterone, and serum dihydroepiandrosterone sulfate). Effectiveness of the strength training program was determined by measuring pre-post differences in: isokinetic strength for flexion and extension at the knee and elbow joints at two speeds (30 degrees and 90 degrees X s-1) (KIN COM, Chattecx, Inc., Chattanooga, TN), flexibility, standing long jump, vertical jump, body composition parameters, maximal oxygen consumption, and creatinine phosphokinase. Safety of strength training was assessed by biphasic musculoskeletal scintigraphy before and after the program and by physician evaluation of complaints by subjects. Strength training subjects (N = 16) participated in a 45 min/session, 3 session/wk, 14-wk supervised strength training program with an attendance rate of 91.5%. Participants performed concentric work using hydraulic resistance equipment (Hydra-Fitness Industries, Belton, TX). Eccentric work was not performed. Control subjects (N = 10) did not strength train but did participate in sport activities and activities of daily living. Results indicated that strength training subjects increased isokinetic strength as a result of strength training (average concentric work/repetition increases by 18.5 to 36.6% for the eight motions tested; torque scores over the first 90% of the range of motion increases by 13.1 to 45.1% for the eight motions tested). These changes were significantly greater than changes seen in the control group (P less than 0.05). Strength training subjects also demonstrated significant improvements (as compared to control subjects) in vertical jump (+10.4%), flexibility (+8.4%), and maximal oxygen consumption [+19.4% (l X min-1), +13.8% (ml X kg X min-1)] after the experimental period. Musculoskeletal scintigraphy revealed no evidence of damage to epiphyses, bone, or muscle as a result of strength training. Only one strength training-related injury was reported (left shoulder pain, 3 strength training sessions missed). In contrast, six strength training subjects sustained injuries during activities of daily living, resulting in 47 missed strength training sessions. It was concluded that, in the short term, supervised concentric strength training using hydraulic resistance equipment is safe and effective in pre-pubertal boys.