Inactive adults experience a 3% to 8% loss of muscle mass per decade, accompanied by resting metabolic rate reduction and fat accumulation. Ten weeks of resistance training may increase lean weight by 1.4 kg, increase resting metabolic rate by 7%, and reduce fat weight by 1.8 kg. Benefits of resistance training include improved physical performance, movement control, walking speed, functional independence, cognitive abilities, and self-esteem. Resistance training may assist prevention and management of type 2 diabetes by decreasing visceral fat, reducing HbA1c, increasing the density of glucose transporter type 4, and improving insulin sensitivity. Resistance training may enhance cardiovascular health, by reducing resting blood pressure, decreasing low-density lipoprotein cholesterol and triglycerides, and increasing high-density lipoprotein cholesterol. Resistance training may promote bone development, with studies showing 1% to 3% increase in bone mineral density. Resistance training may be effective for reducing low back pain and easing discomfort associated with arthritis and fibromyalgia and has been shown to reverse specific aging factors in skeletal muscle.

ABSTRACT. Background. Previous research has shown that children can increase their muscular strength and muscular endurance as a result of regular participation in a progressive resistance training program. However, the most effective exercise prescription regarding the number of repetitions remains questionable.Objective. To compare the effects of a low repetitionheavy load resistance training program and a high repetition-moderate load resistance training program on the development of muscular strength and muscular endurance in children.Design. Prospective, controlled trial. Setting. Community-based youth fitness center. Subjects. Eleven girls and 32 boys between the ages of 5.2 and 11.8 years.Intervention. In twice-weekly sessions of resistance training for 8 weeks, children performed 1 set of 6 to 8 repetitions with a heavy load (n ‫؍‬ 15) or 1 set of 13 to 15 repetitions with a moderate load (n ‫؍‬ 16) on child-size exercise machines. Children in the control group (n ‫؍‬ 12) did not resistance train. One repetition maximum (RM) strength and muscular endurance (repetitions performed posttraining with the pretraining 1-RM load) were determined on the leg extension and chest press exercises.Results. One RM leg extension strength significantly increased in both exercise groups compared with that in the control subjects. Increases of 31.0% and 40.9%, respectively, for the low repetition-heavy load and high repetition-moderate load groups were observed. Leg extension muscular endurance significantly increased in both exercise groups compared with that in the control subjects, although gains resulting from high repetitionmoderate load training (13.1 ؎ 6.2 repetitions) were significantly greater than those resulting from low repetition-heavy load training (8.7 ؎ 2.9 repetitions). On the chest press exercise, only the high repetition-moderate load exercise group made gains in 1-RM strength (16.3%) and muscular endurance (5.2 ؎ 3.6 repetitions) that were significantly greater than gains in the control subjects.Conclusion. These findings support the concept that muscular strength and muscular endurance can be improved during the childhood years and favor the prescription of higher repetition-moderate load resistance training programs during the initial adaptation period. Pediatrics 1999;104(1). URL: http://www.pediatrics.org/ cgi/content/full/104/1/e5; strength training, weight training, exercise, youth, preadolescent.ABBREVIATIONS. RM, repetition maximum; DCER, dynamic constant external resistance. I n the past several years, resistance training has proven to be a safe and effective method of conditioning for children, provided that appropriate exercise guidelines are followed.1-3 Although the capability of children to increase their muscular strength was questioned in the past, 4 current findings suggest that children may benefit from regular participation in resistance training activities. Reports indicate that youth resistance training may improve motor performance skills, 5 may reduce injuries in sports and recre...

Strength training has become an accepted method of conditioning in children. However, there is concern among some observers that maximal strength testing may be inappropriate or potentially injurious to children. The purpose of this study was to evaluate the safety and efficacy of 1 repetition maximum (1RM) strength testing in healthy children. Thirty-two girls and 64 boys between 6.2 and 12.3 years of age (mean age 9.3 +/- 1.6 years) volunteered to participate in this study. All subjects were screened for medical conditions that could worsen during maximal strength testing. Under close supervision by qualified professionals, each subject performed a 1RM test on 1 upper-body (standing chest press or seated chest press) and 1 lower-body (leg press or leg extension) exercise using child-size weight training machines. No injuries occurred during the study period, and the testing protocol was well tolerated by the subjects. No gender differences were found for any upper- or lower-body strength test. These findings demonstrate that healthy children can safely perform 1RM strength tests, provided that appropriate procedures are followed.

Despite the widespread use of and acceptance of muscular fitness field tests in national youth fitness test batteries, little is known about how these field tests compare to 1 repetition maximum (1RM) strength in children. Therefore, the aim of this study was to characterize and identify correlates of muscular strength in children 7 to 12 years of age. Ninety children (39 girls and 51 boys) between the ages of 6.7 and 12.3 years volunteered to participate in this study. Children were tested on 1RM chest press (CP) strength, 1RM leg press (LP) strength, handgrip strength, vertical jump, long jump, sit and reach flexibility, and height and weight (used to determine body mass index [BMI]). For the combined sample, LP 1RM ranged from 75% to 363% of body weight and CP 1RM ranged from 25% to 103% of body weight. Multiple regression analyses predicting LP 1RM showed that BMI and long jump were significant (R = 44.4% with age and gender not significant) and BMI and vertical jump were significant (R = 40.8% with age and gender not significant). Multiple regression analyses predicting CP 1RM showed that BMI and handgrip strength were significant (R = 58.6% with age and gender not significant). Age and gender alone accounted for 4.6% (not significant) of the variation in LP 1RM and 15.4% (significant) in CP 1RM. In summary, these data indicate that BMI, handgrip strength, long jump, and vertical jump relate to 1RM strength in children and therefore may be useful for assessing muscular fitness in youths.

To address reduced physical education (PE) in elementary schools, a 12-week physical activity protocol was tested on 5-12-year-old, primarily African American, girls (n = 226) and boys (n = 344) at 14 YMCA after-school care sites. The 3 times/week, 45-min session curriculum included cardiovascular, resistance, and flexibility training, in which all children could participate simultaneously, and a behavioral skills education component. After-school counselors, formerly untrained in PE methods, administered the sessions, with periodic supervision by YMCA wellness staff members. Analyses of the eight Age x Sex subsamples indicated significant improvements on body composition, strength, and endurance, both within-groups and when predicted changes due to maturation were accounted for. Exercise barriers self-efficacy significantly increased in subsamples of 9-10- and 11-12-year-old girls only. The need for replication across ethnic groups was suggested. Limitations and the need for extension of research on supplementation of elementary school PE were discussed.