Dear Editor-in-Chief: Reading the article of Lo¨fgren et al. (2) on physical education (PE) and muscle strength, I was disappointed to find no mention of a similar study completed in Trois Rivie`res 40 yr previously (4). The earlier quasi-experimental investigation examined many aspects of health, including muscle strength, in 546 primary school students; it comprised a test group (60 min of specialist-taught PE daily, maximization of class activity, but no specific resistance training) and controls from adjacent school years (40 minIwkj1 of nonspecialist-taught PE). Dropouts were fewer than 4% per year, and there was little compensatory reduction of physical activity at home, an issue apparently not addressed by Lo¨fgren et al. (2). Tensiometer and dynamometer assessments of six muscle groups were repeated annually for 6 yr. MANOVA analyses showed substantial sex differences of strength at all ages, especially for the arm muscles. Rural students were also stronger than their urban peers, and the test group showed significantly greater strength than controls. During the final 3 yr, program benefits averaged 6.8% (shoulder flexion), 4.2% (elbow flexion), 3.0% (handgrip), 4.7% (hip flexion), 5.8% (knee flexion), and 4.2% (knee extension). Corresponding performance scores were also greater (5), with the test group outperforming controls on all of six measures. Differences averaged 1.2% (45.7-m dash), 2.3% (274-m run), 3.4% (shuttle run), sit-ups (23.8%), standing broad jump (4.2%), and flexed arm hang (29.9%). Arm, thigh, and calf circumferences showed no intergroup differences. Thus, the strength advantage of the experimental group reflected improved neuromuscular coordination rather than muscle hypertrophy, a view supported by other investigators (1,3,6), and in line with the virtual absence of sex steroids at this age. Lo¨fgren et al. (2) reported changes in the performance of children who followed a rather similar enhanced PE program between 8 and 10 yr. Their experimental group demonstrated gains of isokinetic strength in three of eight comparisons, all at the higher velocity (180-Isj1). Possibly, greater coordination was required at the faster speed, although we observed gains during isometric testing. Lo¨fgren

Roy J. Shephard, MBBS, MD (Lond), PhD, DPE, LLD, DSc, FACSM, FFIMS Faculty of Kinesiology and Physical Education University of Toronto Toronto, ON, Canada DOI: 10.1249/MSS.0b013e3182a409ec The author of this letter declares no conflict of interest.

REFERENCES 1. Blimkie CJ. Resistance training during preadolescence. Issues and controversies. Sports Med. 1993;15(6):389–407. 2. Lo¨fgren B, Daly RM, Nilsson J-A, Dencker M, Karlsson MK. An increase in school-based physical education increases muscle strength in children. Med Sci Sports Exerc. 2013;45(5):997–1003. 3. Ramsay JA, Blimkie CJ, Smith K, Garner S, MacDougall JD. Strength training effects in prepubertal boys. Med Sci Sports Exerc. 1990;22(5):605–14. 4. Shephard RJ, Lavalle´e H. Impact of enhanced physical education on muscle strength of the prepubescent child. Pediatr Exerc Sci. 1994;6(1):75–87. 5. Shephard RJ, Lavalle´e H. Changes of physical performance as indicators of the response to enhanced physical education. J Sports Med Phys Fitness. 1994;34(4):323–35. 6. Weltman JA, Janney C, Rians CB, et al. The effects of hydraulic resistance training in prepubertal males. Med Sci Sports Exerc. 1986;18(6):629–38.

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et al. (2) also saw an increased vertical jump height and lean body mass, but only in girls, whereas with our larger sample, we found consistent gains of field performance in both sexes, particularly in strength-dependent measures. A discouraging finding from the Malmo˜ study was that those receiving enhanced PE gained body fat. Forty years ago, few students in Trois Rivie`res were overweight. We did not observe any increase of skinfolds in experimental students, but they did not lose body fat relative to their peers. In terms of public policy, increased PE is sometimes advocated to counter the ‘‘obesity epidemic,’’ but in the absence of a dietary intervention, primary school PE seems unlikely either to reduce body fat or to enhance lean tissue mass. Immediate effects are improved neuromuscular coordination, and the building of habits that may carry over into adult life. Our Trois Rivie`res experience suggests a small positive influence upon attitudes and behavior during middle age, but more information is needed on this issue.

Increased Physical Education and Muscle Strength of Primary School Students