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The purpose of the present report was to provide test- and position-specific normative reference values for combine test results based on a large, nationally representative sample of high school-aged American football players in their freshman, sophomore, and junior classes. Cross-sectional anthropometric and performance data were obtained from 12 different high school American football recruiting combines between March 7, 2015, and January 9, 2016, across the United States. Subjects included a sample (n = 7,478) of high school-aged American football athletes in their junior (n = 3,779), sophomore (n = 2,514), and freshman (n = 1,185) classes. The database included combine date, school state, position, class, height, body mass (BM), 40-yard dash, pro-agility, 3-cone, vertical jump, broad jump, and power push-up. Each player self-classified their American football positions as defensive back, defensive end, defensive linemen, linebacker, offensive linemen, quarterback, running back, tight end (TE), or wide receiver. Test- and position-specific normative values were generated by aggregating data from freshman, sophomore, and junior classes. Mean differences were found among classes for all positions and all measurements (p ≤ 0.05), except for TE BM (p > 0.05). Greater differences for all variables were observed from freshman to sophomore classes than from sophomore to junior classes. These normative reference values may provide realistic comparisons and evaluations in performance for young American football players, parents, and coaches with collegiate football aspirations. High school strength and conditioning professionals should use these norms to set attainable goals and reward accomplishments for young football players. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study was to determine magnitudes of differences for anthropometric and athletic performance scores between high school and elite college-level American football players., Method: Participants included high school-age (n = 3,666) athletes who participated in American football combines, as well as elite college-level (n = 5,537) athletes who participated in the National Football League (NFL) scouting combine. Combine data included position; height; weight; 10-, 20-, and 40-yard dash; pro-agility (PA); L-cone drill (LC); vertical jump (VJ); and broad jump (BJ). Athletes were separated into their respective position group, defensive back (DB), wide receiver (WR), linebacker (LB), quarterback (QB), running back (RB), tight end (TE), defensive line (DL), and offensive line (OL) for analysis of performance differences. Percent differences for each dependent variable were calculated to quantify magnitudes of differences., Results: NFL combine participants scored 3% to 25% better on all measurements, with the largest differences between weight and VJ (14%-25%)., Conclusion: The largest measurement-specific differences between high school-age and elite college-level American football players were body size and power. Although it may seem intuitive that elite college-level players would perform better, these data provide a unique perspective to high school players, parents, and coaches, giving new information to use when designing measurement-specific athletic development programs. Thus, strength and conditioning professionals may benefit from emphasizing increases in muscle mass and power output in strength and conditioning programs.

Mendez, AI, Miramonti, AA, Gillen, ZM, McKay, BD, Leutzinger, TJ, and Cramer, JT. Stature, body mass, and BMI in high school american football players: Appropriate determinants of obesity prevalence? J Strength Cond Res 32(11): 3119-3126, 2018-The purpose of this study was to evaluate stature (HT), mass (BM), body mass index (BMI), and obesity prevalence based on BMI categories in a large sample (n = 7,175) of high school American football players enrolled as freshmen, sophomores, or juniors. Players were categorized by their positions: offensive linemen (OLs), defensive linemen (DLs), tight end, defensive end, linebacker, running back, quarterback, defensive back, and wide receiver. The HT, BM, and BMI increased as grade increased among all positions. Offensive lineman and DL had the greatest HT, BM, and BMI (p ≤ 0.05). Obesity prevalence was greatest in OL and DL. When accounting for age-related increases in BMI, BM increased to a greater degree than HT. If HT is an indirect indicator of skeletal size, although BM is more influenced by soft tissue, then the age-related BMI increases in this study may be largely accounted for by soft-tissue changes rather than skeletal growth. Although obesity prevalence in OL (94.5%) and DL (78.4%) positions was greater than all other positions as determined from BMI, it is impossible to know the allocations of fat-free and fat mass-particularly in American football athletes. If obesity continues to be defined as an unhealthy accumulation of fat, then athletes who may have a greater relative proportion of lean soft tissue should not be classified as obese using BMI (BM ÷ HT). More sophisticated, reliable, and sensitive measure of body composition, such as skinfolds, may be more appropriate field measurements.

Purpose: The purpose of this study was to examine the influence of electrode placement over the estimated innervation zone (IZ) for the vastus lateralis, as well as proximal and distal to the estimated IZ, on the isometric torque-related patterns for electromyographic (EMG) amplitude and mean power frequency (MPF)., Methods: Eleven men performed submaximal to maximal isometric muscle actions of the dominant leg extensors. Surface EMG signals were recorded simultaneously from the vastus lateralis muscle with bipolar electrode arrangements placed over the estimated IZ, as well as proximally and distally to the estimated IZ., Results: The results indicate that the patterns of response and mean values for absolute and normalized EMG amplitude and MPF versus isometric torque over the estimated IZ were not consistently different from those away from the IZ. There were, however, mean differences among electrode-placement sites for absolute EMG amplitude values (distal site > proximal and/or estimated IZ sites by approximately 76 microVrms) that were not eliminated with normalization (proximal site > distal and/or estimated IZ sites by approximately 5% max)., Conclusion: Although these differences were not attributable to the IZ, they suggest that during isometric muscle actions, normalized EMG amplitude values from different individuals cannot be compared if the EMG signals are detected from different electrode locations over the muscle of interest.

The aims of this study were to examine the acute effects of static stretching on peak torque, work, the joint angle at peak torque, acceleration time, isokinetic range of motion, mechanomyographic amplitude, and electromyographic amplitude of the rectus femoris during maximal concentric isokinetic leg extensions at 1.04 and 5.23 rad x s(-1) in men and women. Ten women (mean +/- s: age 23.0 +/- 2.9 years, stature 1.61 +/- 0.12 m, mass 63.3 +/- 9.9 kg) and eight men (age 21.4 +/- 3.0 years, stature 1.83 +/- 0.11 m, mass 83.1 +/- 15.2 kg) performed maximal voluntary concentric isokinetic leg extensions at 1.04 and 5.23 rad x s(-1). Following the initial isokinetic tests, the dominant leg extensors were stretched using four static stretching exercises. After the stretching, the isokinetic tests were repeated. Peak torque, acceleration time, and electromyographic amplitude decreased (P< or = 0.05) from pre- to post-stretching at 1.04 and 5.23 rad . s(-1); there were no changes (P > 0.05) in work, joint angle at peak torque, isokinetic range of motion, or mechanomyographic amplitude. These findings indicate no stretching-related changes in the area under the angle - torque curve (work), but a significant decrease in peak torque, which suggests that static stretching may cause a "flattening" of the angle - torque curve that reduces peak strength but allows for greater force production at other joint angles. These findings, in conjunction with the increased limb acceleration rates (decreased acceleration time) observed in the present study, provide tentative support for the hypothesis that static stretching alters the angle - torque relationship and/or sarcomere shortening velocity.