Isokinetic concentric quadriceps and hamstring normative data for elite collegiate American football players participating in the NFL Scouting Combine.

Isokinetic concentric quadriceps and hamstring strength data using a Cybex dynamometer are collected for elite collegiate American football players invited to the annual National Football League Scouting Combine. We constructed a normative (reference) database of the Cybex strength data for the purpose of allowing comparison of an individual's values to his peers. Data reduction was performed to construct frequency distributions of hamstring/quadriceps (H/Q) ratios and side-to-side strength differences. For the cohort (n = 1,252 players), a statistically significant but very small (1.9%) mean quadriceps strength preference existed for dominant side vs. nondominant side. Peak torque (Newton meters, best repetition) for quadriceps and hamstrings was significantly correlated to player body mass (weight) (the same relationship was found for other variables using peak torque in the calculation). Peak torque varied by player position, being greatest for offensive linemen and lowest for kickers (p < 0.0001). Adjusting for body weight overcorrected these differences. The H/Q ratios and frequency distributions were similar across positions, with a mean of 0.6837 ± 0.137 for the cohort dominant side vs. 0.6940 ± 0.145 for the nondominant side (p = 0.021, n = 1,252). Considerable variation was seen for dominant-to-nondominant side difference for peak torque. For quadriceps, 47.2% of players had differences between -10% and +10%, 21.0% had a peak torque dominant-side deficit of 10% or greater compared to nondominant side, and for 31.8% of players, dominant-side peak torque was greater than 10% compared to nondominant side. For hamstrings, 57.0% of players had differences between -10% and +10%, 19.6% had a peak torque dominant-side deficit of 10% or greater compared to nondominant side, and 23.4% of players, dominant-side peak torque was greater than 10% compared to nondominant side. We observed that isokinetic absolute strength variables are dependent on body weight and vary across player position. The H/Q ratios vary only within a relatively narrow range. Side-to-side differences in strength variables >10% are common, not the exception.

Isokinetic concentric quadriceps and hamstring strength variables from the NFL Scouting Combine are not predictive of hamstring injury in first-year professional football players.

BACKGROUND: There are conflicting reports regarding the association between isokinetic concentric quadriceps and hamstring strength deficits and ratios and risk for hamstring injuries in athletes. PURPOSE: To determine if isokinetic concentric Cybex data collected during the annual National Football League (NFL) Scouting Combine are predictive of hamstring injury in professional American football players during their first season. STUDY DESIGN: Case-control study; Level of evidence, 3. METHODS: All 32 NFL teams identified players selected during the first 5 rounds of the NFL annual draft who had hamstring injuries during their first professional season. Of these, 164 players with 172 injuries also had Cybex data from the previous year's Combine. Analyses compared injured legs with contralateral uninjured legs and also injured players with uninjured controls using a database of Cybex data from all players who participated in the NFL Scouting Combine from 2006 to 2011. RESULTS: No Cybex strength variable differentiated the injured legs from the contralateral uninjured legs or injured players from uninjured controls, even after taking into account days lost from activity. Mean ± SD peak torque for the injured and contralateral uninjured sides was as follows: 315.7 ± 70.0 and 313.5 ± 68.3 N · m, respectively (P = .773, paired t test), for quadriceps and 203.0 ± 42.4 and 205.3 ± 42.5 N · m, respectively (P = .608, paired t test), for hamstrings. The sensitivity and specificity for the hamstrings-to-quadriceps ratio predicting hamstring injury were 0.513 (95% confidence interval, 0.419-0.607) and 0.524 (0.495-0.554), indicating that the hamstrings-to-quadriceps ratio was not a useful predictor of injury (calculation used the mean ± SD ratio for injured legs, 0.656 ± 0.133). Side-to-side peak torque differences were also not predictive of injury, with more than a 10% difference (plus or minus) occurring commonly in both injured and uninjured players for quadriceps (53% prevalence for both injured and uninjured) and hamstrings (injured, 41% prevalence; uninjured, 43% prevalence). CONCLUSION: Isokinetic strength data collected from collegiate players at the NFL Scouting Combine were not useful for predicting risk of hamstring injury in subsequent professional NFL competition. These data call into question commonly accepted assumptions about risk factors for hamstring injury, at least for elite collegiate American football players, when the temporal relationship between Cybex testing and actual injury is several months.