Author(s): Jesse Hadfield, Lee J. Hinkle
Mentor(s): A. Wayne Johnson
Institution BYU
Many studies have determined hamstrings are one of the most common sports injuries. Further studies have found that the performance of Nordic hamstring exercises results in a lower incidence of hamstring injuries. Accordingly, assessment of hamstring strength can be a powerful predictor of risk of injury. In a previous study in our lab, a model for predicting hamstring strength was developed by testing eccentric hamstring strength using a Nordbord device. However, the study involved a limited number of participants which is a severe limitation in model development. PURPOSE: This study aims to compare the previously developed model to find which variables are the best predictors of total hamstring force. The model indicates Total Force is best predicted by height (cm), weight (kg), sex, estimated volume, average echo intensity (avgEI), and weekly walking hours (adj-R2 = 0.77, F=15.06 on 6/19 degrees of freedom, p=2.6E-6, BIC = 346.99). METHODS: A survey was administered to 27 (F = 13, age: , height: 172 ± 11 cm, weight 73.5 ± 15.4 kg) participants where they self-reported variables including age, sex, and completed the International Physical Activity Questionnaire (IPAQ). Then, the participants were assessed using a Nordbord device to find hamstring strength and imbalance. Ultrasounds were taken and analyzed with OsiriX to measure predicted values for echo intensity and estimated hamstring volume. Finally, linear models predicting total hamstring force from sex, age, height, weight, volume, echo intensity, estimated volume, and several IPAQ measurements of weekly physical exercise intensity. One participant was left out of model development because of missing data in the responses. RESULTS: The best model used only age, echo intensity, and weight to predict total force (adj-R2=0.83, F=41.9 on 3/22 df, p = 2.9E-9 BIC=333.22). CONCLUSION: This data confirmed some of the conclusions gleaned from the previous study, including the importance of echo intensity and age in predicting total force; however, it also revealed a few surprises. Among the 26 participants evaluated, height, sex, and estimated hamstring volume had little bearing on hamstring strength. This is interesting because it suggests that hamstring strength is not significantly tied to the size of the muscle or influenced by the gender of the individual. By far, weight was the strongest predictor of hamstring force. This could suggest that strength in the hamstrings is generated by increased demands of supporting a larger frame. Overall, the study determined that for this set of participants, a much simpler model for predicting strength could be generated by focusing measurements on age, weight, and echo intensity.