Normalized isokinetic peak hip extensor torque was 42% greater in males (2.4 ± 0.5 N·m·kg−1, P < 0.05) compared to females (1.8 ± 0.4 N·m·kg−1). Similarly, normalized isokinetic peak abductor toque was also greater in males (1.3 ± 0.2 N·m·kg−1, P < 0.05) compared to females (1.0 ± 0.2 N·m·kg−1).
We hypothesized that, as hip strength increased, thorax and pelvic motion would decrease during treadmill running in a cohort of collegiate cross-country runners. This hypothesis was supported as the subjects in the current study exhibited significant negative correlations of hip abductor and extensor strength to pelvic and thorax ROM. From a neuromuscular standpoint, enhanced strength of the pelvic complex during the stance phase of running has been acknowledged to be an important predictive factor in a variety of lower extremity injuries (1,13,16,19,24). Further, targeted gluteal strengthening programs have demonstrated improvements in subjects’ gluteal strength (6,34,39) and reduced pain with corresponding improvements in function (6,13,21). While a causal relationship between strength and thorax motion cannot be gleaned from this study, a potential relationship is indicated from the results of this study. What remains unclear is whether improving gluteal strength alters running mechanics, with recent studies with a control group for comparison indicating short-term gluteal strengthening does not affect knee mechanics (6,39); however, further investigations are warranted using different strengthening tools, time frames, and feedback to adequately assess this latter point.
Anatomically, the gluteus maximus connects the pelvis to the thoracic and lumbar spine via the posterior layer of the thoracolumbar fascia and hence tensioning of the gluteus maximus may impact axial rotation (37). Nyland et al. (26) were able to show that whole-body, long-axis rotational training of the trunk improved lower extremity mechanics, improved ground reaction force stabilization, and increased gluteus maximus and gluteus medius neuromuscular efficiency during a single-leg lateral drop landing and stabilization test. The training group used a specialized training device with the subjects’ feet planted on the ground, standard and diagonal, as they performed concentric and eccentric trunk rotation exercise.
Sex differences were evident in our cohort in hip strength and pelvic and thorax motion. Previous studies support that females have increased lower extremity frontal plane motion in a variety of movements, including during the stance phase of running when compared to male counterparts (2,7,8,10–12,18,20,28,32,33). However, sex differences in transverse plane trunk axial rotation during running are modestly reported in the literature. In support of our current findings, Schache et al. (32) compared running mechanics between sexes and found that females had increased axial trunk rotation (marker rod positioned over the twelfth thoracic spinous process) when calculated in relation to the pelvis. Interestingly, these differences were primarily explained by sex as opposed to a variety of anthropometric and dynamic variables (32). In a later study, Saunders et al. (30) report increasing speed leads to reduced axial rotation across sexes; however, their study is limited by both a paucity of total subjects (n = 7) and female subjects (n = 1), which limits comparisons to the current study.
Average hip strength differences between male and female groups were similar to previous studies. Using the same hip abduction strength procedure on 21 females, Myer et al. (23) found average peak hip abduction strength of 0.99 N·m·kg−1, which is similar to the hip strength found on our female population. Jacobs et al. (17) studied hip abduction function in males and females and found that females had significantly decreased peak torque when compared to males. Males have been found to have 41% higher maximum hip extension strength than females do (14). While the mechanism is not fully understood, an increase in hip strength has been shown to decrease frontal and transverse plane lower extremity motion in running (34). This supports our findings that the amount of hip strength relates to the amount of rotation and obliquity in neighboring joints. Dowson et al. (4) measured hip extension isokinetic strength at 190°·s−1 in a population of sprinters. They found average peak strength relative to body mass as 2.92 N·m·kg−1, which is higher than the average found in this study, which may be explained by the difference in population.
Clinically, the relationship between strength and function is often investigated in runners. The results of this study indicate that a significant inverse relationship exists between hip strength and rotations in the frontal and transverse planes during treadmill running. In addition, in patients with large movement excursions in the transverse plane, which are easily identified during visual gait observations, clinicians should pay close attention to potential gluteal strength deficits. This important relationship should be further explored with investigations targeting the effects of gluteal strengthening on lumbopelvic trunk rotation and any corresponding effects on pain, biomechanics, and function.
It is important to note that all running analyses in the current study were performed on a treadmill and therefore may not be generalizable to overground running. Treadmill analyses were used to standardize running conditions across all subjects. We assessed pelvic drop as a segmental angle in relation to the global laboratory coordinate system. Several studies have reported hip abduction/adduction as thigh rotation about the pelvis. Therefore, relative pelvic obliquity (drop) motion may pertain to several reports of hip frontal plane motion that are reported as joint angles. In addition, the use of segmental angles for both the pelvis and thorax should be carefully interpreted when comparing against other biomechanical conventions.
In conclusion, we identified moderate correlations in hip extensor and hip abductor strength and pelvic and thorax motion during running. The potential that a causal relationship may exist should be further investigated with randomized trials that target gluteal strengthening. In addition, females exhibited decreased strength and increased pelvic and thorax motion compared to males. While not in the scope of this study, future work should identify the effects of thorax motion on lower extremity mechanics and risk of overuse running injuries.
This work was supported by Cincinnati Children’s Hospital Research Foundation.
The authors would also like to thank adidas for donating the shoes for this study and the coaches and athletes from the University of Cincinnati Cross Country Team for participation. External funding was not received for this study.
There is no conflict of interest for each author of this study.
The results of this study do not constitute endorsement by the American College of Sports Medicine.
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