Normative Reference Values for High School-Aged American Football Players: Proagility Drill and 40-Yard Dash Split Times

McKay, BD, Miramonti, AA, Gillen, ZM, Leutzinger, TJ, Mendez, AI, Jenkins, NDM, and Cramer, JT. Normative reference values for high school-aged American football players: Proagility drill and 40-yard dash split times. J Strength Cond Res 34(4): 1184-1187, 2020-The purpose of this short report was to provide test- and position-specific normative reference values for the 10- and 20-yd split times (10YD and 20YD) during the 40-yd dash (40YD) as well as 10-yd split times during the proagility drill (PA) based on a large, nationally representative sample of high school-aged American football players in their freshman, sophomore, and junior classes. Cross-sectional 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. The sample included (n = 7,478) high school-aged American football athletes in their freshman (n = 1,185), sophomore (n = 2,514), and junior (n = 3,779) classes. Each player self-classified their American football positions as defensive back, defensive end, defensive linemen, linebacker, offensive linemen (OL), quarterback (QB), running back, tight end, or wide receiver. The results of the freshman, sophomore, and junior class were aggregated to generate test- and position-specific normative values. Mean differences were found among classes for all positions and all measurements (p ≤ 0.05) except for OL and QB PA split time (p > 0.05). Greater percent differences for all 3 variables were observed between freshman and sophomore years than between sophomore and junior years. These normative reference values will be useful for athletes, parents, coaches, and high school strength and conditioning professionals to set realistic goals for young American football athletes.

Normative Reference Values for High School-Aged American Football Players

McKay, BD, Miramonti, AA, Gillen, ZM, Leutzinger, TJ, Mendez, AI, Jenkins, NDM, and Cramer, JT. Normative reference values for high school-aged American football players. J Strength Cond Res 34(10): 2849-2856, 2020-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.

Test-Retest Reliability and Concurrent Validity of Athletic Performance Combine Tests in 6-15-Year-Old Male Athletes

Gillen, ZM, Miramonti, AA, McKay, BD, Leutzinger, TJ, and Cramer, JT. Test-retest reliability and concurrent validity of athletic performance combine tests in 6-15-year-old male athletes. J Strength Cond Res 32(10): 2783-2794, 2018-Athletic performance combine tests are used by high school, collegiate, and professional American football programs to evaluate performance; however, limited evidence is available on performance combine test results in youth athletes. The purposes of this study were to report test-retest reliability statistics and evaluate concurrent validity among combine performance tests in 6-15-year-old male athletes. Sixty-nine young male athletes (mean ± SD; age = 10.9 ± 2.1 years, height = 154.4 ± 13.6 cm, body mass = 46.8 ± 16.0 kg) were divided into 3 age groups: 6-9 years (n = 16), 10-11 years (n = 26), and 12-15 years (n = 27). Participants completed 2 attempts of the vertical jump (VJ), broad jump (BJ), pro-agility (PA), L-cone (LC) drill, and 10-, 20-, 40-yd dashes. The results indicated that the older age groups performed better on most performance assessments compared with the 6-9-year group (p ≤ 0.05). The combine tests demonstrated consistently adequate reliability for all age groups, except for the 10-yd dash, which was deemed unreliable. Evidence of concurrent validity, and possible measurement redundancy were observed in the VJ vs. BJ, PA vs. LC, and 20 vs. 40 yd, but zero- and first-order partial correlations suggested that only the PA and LC were redundant, and the PA may be superior for this age group over the LC. Although the VJ and BJ provide independent performance information regarding lower-body power, questions regarding the redundancy of the 20 vs. 40 yd remain unanswered from a measurement perspective.

Anthropometric and Athletic Performance Combine Test Results Among Positions Within Grade Levels of High School-Aged American Football Players

Leutzinger, TJ, Gillen, ZM, Miramonti, AM, McKay, BD, Mendez, AI, and Cramer, JT. Anthropometric and athletic performance combine test results among positions within grade levels of high school-aged American football players. J Strength Cond Res 32(5): 1288-1296, 2018-The purpose of this study was to investigate differences among player positions at 3 grade levels in elite, collegiate-prospective American football players. Participants' data (n = 7,160) were analyzed for this study (mean height [Ht] ± SD = 178 ± 7 cm, mass [Bm] = 86 ± 19 kg). Data were obtained from 12 different high school American football recruiting combines hosted by Zybek Sports (Boulder, Colorado). Eight 2-way (9 × 3) mixed factorial analysis of variances {position (defensive back [DB], defensive end, defensive lineman, linebacker, offensive lineman [OL], quarterback, running back, tight end, and wide receiver [WR]) × grade (freshmen, sophomores, and juniors)} were used to test for differences among the mean test scores for each combine measure (Ht, Bm, 40-yard [40 yd] dash, proagility [PA] drill, L-cone [LC] drill, vertical jump [VJ], and broad jump [BJ]). There were position-related differences (p ≤ 0.05) for Ht, 40 yd dash, and BJ, within each grade level and for Bm, PA, LC, and VJ independent of grade level. Generally, the results showed that OL were the tallest, weighed the most, and exhibited the lowest performance scores among positions. Running backs were the shortest, whereas DBs and WRs weighed the least and exhibited the highest performance scores among positions. These results demonstrate the value of classifying high school-aged American football players according to their specific position rather than categorical groupings such as "line" vs. "skill" vs. "big skill" when evaluating anthropometric and athletic performance combine test results.

Reliability and Sensitivity of the Power Push-up Test for Upper-Body Strength and Power in 6-15-Year-Old Male Athletes

Gillen, ZM, Miramonti, AA, McKay, BD, Jenkins, NDM, Leutzinger, TJ, and Cramer, JT. Reliability and sensitivity of the power push-up test for upper-body strength and power in 6-15-year-old male athletes. J Strength Cond Res 32(1): 83-96, 2018-The power push-up (PPU) test is an explosive upper-body test performed on a force plate and is currently being used in high school football combines throughout the United States. The purpose of this study was to quantify the reliability of the PPU test based on age and starting position (knees vs. toes) in young athletes. Sixty-eight boys (mean ± SD; age = 10.8 ± 2.0 years) were tested twice over 5 days. Boys were separated by age as 6-9 years (n = 16), 10-11 years (n = 26), and 12-15 years (n = 26). The PPU test was performed on a force plate while rotating from the knees vs. the toes. Measurements were peak force (PF, N), peak rate of force development (pRFD, N·s), average power (AP, W), and peak power (PP, W). Intraclass correlation coefficients (ICC2,1), SEMs, coefficients of variation (CVs), and minimum detectable changes (MDCs) were calculated to quantify reliability and sensitivity. Peak force from the knees in 10-15-year-olds, PF from the toes in 12-15-year-olds, and pRFD from the knees and toes in 12-15-year-olds were comparably reliable (ICC ≥ 0.84). Neither power measurements (AP or PP) for any age group, nor any measurements (PF, pRFD, AP, or PP) for the 6-9-year-olds were comparably reliable (ICC ≤ 0.74). When considering the reliable variables, PF was greater in the 12-15-year-olds than in 10-11-year-olds (p ≤ 0.05). In addition, in 12-15-year-olds, PF and pRFD were greater from the knees than from the toes (p ≤ 0.05). For reasons largely attributable to growth and development, the PPU test may be a reliable (ICC ≥ 0.80) and sensitive (CV ≤ 19%) measure of upper-body strength (PF), whereas pRFD was also reliable (ICC ≥ 0.80), but less sensitive (CV = 30-38%) in 10-15-year-old male athletes.

Influence of stretching velocity on musculotendinous stiffness of the hamstrings during passive straight-leg raise assessments

BACKGROUND

Recently, passive musculotendinous stiffness (MTS) has been assessed manually in the field; however, when conducting these types of assessments, the stretching velocity must be controlled to avoid eliciting the stretch reflex, which can be observed by increased electromyographic (EMG) amplitude of the stretched muscles and greater resistive torque (indicating the assessment is no longer passive).

OBJECTIVE

To examine the effects of slow, medium, and fast stretching velocities during manually-applied passive straight-leg raise (SLR) assessments on hamstrings MTS and EMG amplitude characteristics.

STUDY DESIGN

Crossover study.

METHODS

Twenty-three healthy, young adults underwent passive, manually-applied SLR assessments performed by the primary investigator at slow, medium, and fast stretching velocities. During each SLR, MTS and EMG amplitude were determined at 4 common joint angles (?) separated by 5° during the final common 15° of range of motion for each participant.

RESULTS

The average stretching velocities were 7, 11, and 18°·s^?1 for the slow, medium, and fast SLRs. There were no velocity-related differences for MTS (P = 0.489) or EMG amplitude (P = 0.924). MTS increased (P < 0.001) with joint angle (?₁<?₂<?₃<?₄); however, EMG amplitude remained unchanged (P = 0.885) across the range of motion.

CONCLUSIONS

Although velocity discrepancies have been identified as a potential threat to the validity of passive MTS measurements obtained with manual SLR techniques, the present findings suggest that the SLR at any of the velocities tested in our study (7-18°·s^?1) did not elicit a detectible stretch reflex, and thereby may be appropriate for examining MTS.

Exertional Rhabdomyolysis in a 21-Year-Old Healthy Woman: A Case Report

McKay, BD, Yeo, NM, Jenkins, NDM, Miramonti, AA, and Cramer, JT. Exertional rhabdomyolysis in a 21-year-old healthy woman: a case report. J Strength Cond Res 31(5): 1403-1410, 2017-The optimal resistance training program to elicit muscle hypertrophy has been recently debated and researched. Although 3 sets of 10 repetitions at 70-80% of the 1 repetition maximum (1RM) are widely recommended, recent studies have shown that low-load (∼30% 1RM) high-repetition (3 sets of 30-40 repetitions) resistance training can elicit similar muscular hypertrophy. Incidentally, this type of resistance training has gained popularity. In the process of testing this hypothesis in a research study in our laboratory, a subject was diagnosed with exertional rhabdomyolysis after completing a resistance training session that involved 3 sets to failure at 30% 1RM. Reviewed were the events leading up to and throughout the diagnosis of exertional rhabdomyolysis in a healthy recreationally-trained 21-year-old woman who was enrolled in a study that compared the acute effects of high-load low-repetition vs. low-load high-repetition resistance training. The subject completed a total of 143 repetitions of the bilateral dumbbell biceps curl exercise. Three days after exercise, she reported excessive muscle soreness and swelling and sought medical attention. She was briefly hospitalized and then discharged with instructions to take acetaminophen for soreness, drink plenty of water, rest, and monitor her creatine kinase (CK) concentrations. Changes in the subject's CK concentrations, ultrasound-determined muscle thickness, and echo intensity monitored over a 14-day period are reported. This case illustrates the potential risk of developing exertional rhabdomyolysis after a low-load high-repetition resistance training session in healthy, young, recreationally-trained women. The fact that exertional rhabdomyolysis is a possible outcome may warrant caution when prescribing this type of resistance exercise.

Greater Neural Adaptations following High- vs. Low-Load Resistance Training

We examined the neuromuscular adaptations following 3 and 6 weeks of 80 vs. 30% one repetition maximum (1RM) resistance training to failure in the leg extensors. Twenty-six men (age = 23.1 ± 4.7 years) were randomly assigned to a high- (80% 1RM; n = 13) or low-load (30% 1RM; n = 13) resistance training group and completed leg extension resistance training to failure 3 times per week for 6 weeks. Testing was completed at baseline, 3, and 6 weeks of training. During each testing session, ultrasound muscle thickness and echo intensity, 1RM strength, maximal voluntary isometric contraction (MVIC) strength, and contractile properties of the quadriceps femoris were measured. Percent voluntary activation (VA) and electromyographic (EMG) amplitude were measured during MVIC, and during randomly ordered isometric step muscle actions at 10–100% of baseline MVIC. There were similar increases in muscle thickness from Baseline to Week 3 and 6 in the 80 and 30% 1RM groups. However, both 1RM and MVIC strength increased from Baseline to Week 3 and 6 to a greater degree in the 80% than 30% 1RM group. VA during MVIC was also greater in the 80 vs. 30% 1RM group at Week 6, and only training at 80% 1RM elicited a significant increase in EMG amplitude during MVIC. The peak twitch torque to MVIC ratio was also significantly reduced in the 80%, but not 30% 1RM group, at Week 3 and 6. Finally, VA and EMG amplitude were reduced during submaximal torque production as a result of training at 80% 1RM, but not 30% 1RM. Despite eliciting similar hypertrophy, 80% 1RM improved muscle strength more than 30% 1RM, and was accompanied by increases in VA and EMG amplitude during maximal force production. Furthermore, training at 80% 1RM resulted in a decreased neural cost to produce the same relative submaximal torques after training, whereas training at 30% 1RM did not. Therefore, our data suggest that high-load training results in greater neural adaptations that may explain the disparate increases in muscle strength despite similar hypertrophy following high- and low-load training programs.

Reliability and Minimum Detectable Change for Common Clinical Physical Function Tests in Sarcopenic Men and Women

OBJECTIVES

To determine the test-retest reliability and minimum detectable change scores for seven common clinical measurements of muscle strength and physical function in a multiethnic sample of sarcopenic, malnourished men and women.

DESIGN

Each participant visited the laboratory seven times over 25 to 26 weeks. Reliability was assessed for each measurement from Familiarization 1 to Familiarization 2 (R1), Familiarization 2 to baseline testing (R2), Familiarization 3 to 12-week testing (R3), and Familiarization 4 to 24-week testing (R4).

SETTING

Data were collected during a clinical trial at 23 sites in the United States, Belgium, Italy, Mexico, Poland, Spain, Switzerland, and the United Kingdom.

PARTICIPANTS

Sarcopenic, malnourished, older adults (N = 257; n = 98 men aged 76.8 ± 6.3, n = 159 women aged 75.9 ± 6.6).

MEASUREMENTS

During each visit, participants completed the Short Physical Performance Battery (SPBB) and isometric handgrip and isokinetic leg extensor and flexor strength testing at a slow (1.05 rad/s) and fast (3.15 rad/s) velocity.

RESULTS

Handgrip strength, gait speed, SPPB score, and isokinetic leg extension and flexion peak torque (PT) had intraclass correlation coefficients (ICCs) that were significantly greater than 0 (all ≥0.59) at R1, R2, R3, and R4, although most of these variables demonstrated systematic increases at R1, and several exhibited systematic variability beyond the baseline testing session.

CONCLUSION

The ICCs and standard errors of the measurement (SEMs) generally improved with familiarization, which emphasizes the need for at least one familiarization trial for these measurements in sarcopenic, malnourished older adults. A three tier-approach to interpreting the clinical importance of statistically significant results that includes null hypothesis testing, examination and interpretation of the effect magnitude, and comparison of individual changes with the SEM and minimum detectable change of the measurements used is recommended.

Mechanomyographic responses during recruitment curves in the soleus muscle

INTRODUCTION

In this study we examined relationships among mechanomyographic (MMG), electromyographic (EMG), and peak twitch torque (PTT) responses as well as test-retest reliability when recorded during recruitment curves in the soleus muscle.

METHODS

PTT, EMG (M-wave, H-reflex), and MMG responses were recorded during recruitment curves in 16 subjects (age 24 ± 2 years) on 2 separate days. The sum of the M-wave and H-reflex (M+H) was calculated. Correlations among variables and test-retest reliability were determined.

RESULTS

MMG was correlated with PTT (mean r = 0.93, range r = 0.59-0.99), the M-wave (0.95, 0.04-0.98), and M+H (0.91, 0.42-0.97), but was unrelated to the H-reflex (-0.06, -0.56 to 0.47). Reliability was consistently high among most variables, but normalizing to the maximum value improved MMG reliability and the minimum detectable change.

CONCLUSION

MMG responses predicted 86%-90% of the variability in PTT, M-wave, and M+H; thus, MMG may be a useful alternative for estimating twitch torque and maximal activation. Muscle Nerve 56: 107-116, 2017.

Electromyographic Responses from the Vastus Medialis during Isometric Muscle Actions

This study examined the electromyographic (EMG) responses from the vastus medialis (VM) for electrodes placed over and away from the innervation zone (IZ) during a maximal voluntary isometric contraction (MVIC) and sustained, submaximal isometric muscle action. A linear electrode array was placed on the VM to identify the IZ and muscle fiber pennation angle during an MVIC and sustained isometric muscle action at 50% MVIC. EMG amplitude and frequency parameters were determined from 7 bipolar channels of the electrode array, including over the IZ, as well as 10 mm, 20 mm and 30 mm proximal and distal to the IZ. There were no differences between the channels for the patterns of responses for EMG amplitude or mean power frequency during the sustained, submaximal isometric muscle action; however, there were differences between channels during the MVIC. The results of the present study supported the need to standardize the placement of electrodes on the VM for the assessment of EMG amplitude and mean power frequency. Based on the current findings, it is recommended that electrode placements be distal to the IZ and aligned with the muscle fiber pennation angle during MVICs, as well as sustained, submaximal isometric muscle actions.