Explore the vast range of titles available.

Background Tibial stress fracture is a debilitating musculoskeletal injury that diminishes the physical performance of individuals who engage in high-volume running, including Service members during basic combat training (BCT) and recreational athletes. While several studies have shown that reducing stride length decreases musculoskeletal loads and the potential risk of tibial injury, we do not know whether stride-length reduction affects individuals of varying stature differently. Methods We investigated the effects of reducing the running stride length on the biomechanics of the lower extremity of young, healthy women of different statures. Using individualized musculoskeletal and finite-element models of women of short (N = 6), medium (N = 7), and tall (N = 7) statures, we computed the joint kinematics and kinetics at the lower extremity and tibial strain for each participant as they ran on a treadmill at 3.0 m/s with their preferred stride length and with a stride length reduced by 10%. Using a probabilistic model, we estimated the stress-fracture risk for running regimens representative of U.S. Army Soldiers during BCT and recreational athletes training for a marathon. Results When study participants reduced their stride length by 10%, the joint kinetics, kinematics, tibial strain, and stress-fracture risk were not significantly different among the three stature groups. Compared to the preferred stride length, a 10% reduction in stride length significantly decreased peak hip ( p  = 0.002) and knee ( p  < 0.001) flexion angles during the stance phase. In addition, it significantly decreased the peak hip adduction ( p  = 0.013), hip internal rotation ( p  = 0.004), knee extension ( p  = 0.012), and ankle plantar flexion ( p  = 0.026) moments, as well as the hip, knee, and ankle joint reaction forces ( p  < 0.001) and tibial strain ( p  < 0.001). Finally, for the simulated regimens, reducing the stride length decreased the relative risk of stress fracture by as much as 96%. Conclusions Our results show that reducing stride length by 10% decreases musculoskeletal loads, tibial strain, and stress-fracture risk, regardless of stature. We also observed large between-subject variability, which supports the development of individualized training strategies to decrease the incidence of stress fracture.

Background Musculoskeletal injuries, such as stress fractures, are the single most important medical impediment to military readiness in the U.S. Army. While multiple studies have established race- and sex-based risks associated with a stress fracture, the role of certain physical characteristics, such as body size, on stress-fracture risk is less conclusive. Methods In this study, we investigated the effects of body size and load carriage on lower-extremity joint mechanics, tibial strain, and tibial stress-fracture risk in women. Using individualized musculoskeletal-finite-element-models of 21 women of short, medium, and tall statures ( n  = 7 in each group), we computed the joint mechanics and tibial strains while running on a treadmill at 3.0 m/s without and with a load of 11.3 or 22.7 kg. We also estimated the stress-fracture risk using a probabilistic model of bone damage, repair, and adaptation. Results Under all load conditions, the peak plantarflexion moment for tall women was higher than those in short women ( p  < 0.05). However, regardless of the load condition, we did not observe differences in the strains and the stress-fracture risk between the stature groups. When compared to the no-load condition, a 22.7-kg load increased the peak hip extension and flexion moments for all stature groups ( p  < 0.05). However, when compared to the no-load condition, the 22.7-kg load increased the strains and the stress-fracture risk in short and medium women ( p  < 0.05), but not in tall women. Conclusion These results show that women of different statures adjust their gait mechanisms differently when running with external load. This study can educate the development of new strategies to help reduce the risk of musculoskeletal injuries in women while running with external load.

Understanding how body-borne mass influences knee loads during running and how to modulate these knee loads may assist efforts to reduce the high rate of knee injuries in military populations. We tested a) the extent a 15-kg body-borne load affects peak and cumulative patellofemoral (PFJ) and tibiofemoral (TFJ) contact forces during running and b) if a 7.5% increase in running cadence modulates these contact forces. Compared with unloaded running, the body-borne load increased peak PFJ contact force (+0.2 body weights; p=0.001) and PFJ impulse (+32 body weights per km; p<0.001). Additionally, greater peak total TFJ contact force (+0.5 body weights; p<0.001) and greater peak medial TFJ contact force (+0.4 body weights; p=0.002) resulted with the added load. Similarly, 85 additional body weights of total TFJ impulse per km (p<0.001) and 65 additional body weights of medial TFJ impulse per km (p<0.001) were noted with the added load. The higher cadence condition reduced peak PFJ force (−0.5 body weights, p<0.001) and PFJ impulse per km (−15 body weights per km, p<0.016). Reduced peak total and peak medial TFJ contact forces (−0.8 body weights, p<0.001; −0.5 body weights, p<0.001, respectively) were also found with higher cadence, while reduced total TFJ and medial TFJ impulse per km (−18.5 body weights per km, p<0.001; −12.2 body weights per km, p<0.001, respectively) were observed. Thus, running with increased cadence eliminated increased knee loads per step but only partially reduced the greater cumulative knee loads per km that resulted with an added 15-kg body-borne load.

Background Equine water treadmills (WTs) are growing in popularity because they are believed to allow for high resistance, low impact exercise. However, little is known about the effect of water height on limb loading. The aim of this study was to evaluate the effect of water height and speed on segmental acceleration and impact attenuation during WT exercise in horses. Three uniaxial accelerometers (sampling rate: 2500 Hz) were secured on the left forelimb (hoof, mid-cannon, mid-radius). Horses walked at two speeds (S1: 0.83 m/s, S2: 1.39 m/s) and three water heights (mid-cannon, carpus, stifle), with a dry WT control. Peak acceleration of each segment was averaged over five strides, attenuation was calculated, and stride frequency was estimated by the time between successive hoof contacts. Linear mixed effects models were used to examine the effects of water height, speed, and accelerometer location on peak acceleration, attenuation and stride frequency ( p  < 0.05). Results Peak acceleration at all locations was lower with water of any height compared to the dry control ( p  < 0.0001). Acceleration was reduced with water at the height of the stifle compared to mid-cannon water height ( p  = 0.02). Water at the height of the stifle attenuated more impact than water at the height of the cannon ( p  = 0.0001). Conclusions Water immersion during treadmill exercise reduced segmental accelerations and increased attenuation in horses. WT exercise may be beneficial in the rehabilitation of lower limb injuries in horses.

During U.S. Army basic combat training (BCT), women are more prone to lower-extremity musculoskeletal injuries, including stress fracture (SF) of the tibia, with injury rates two to four times higher than those in men. There is evidence to suggest that the different injury rates are, in part, due to sex-specific differences in running biomechanics, including lower-extremity joint kinematics and kinetics, which are not fully understood, particularly when running with external load. To address this knowledge gap, we collected computed tomography images and motion-capture data from 41 young, healthy adults (20 women and 21 men) running on an instrumented treadmill at 3.0 m/s with loads of 0.0 kg, 11.3 kg, or 22.7 kg. Using individualized computational models, we quantified the running biomechanics and estimated tibial SF risk over 10 weeks of BCT, for each load condition. Across all load conditions, compared to men, women had a significantly smaller flexion angle at the trunk (16.9%–24.6%) but larger flexion angles at the ankle (14.0%–14.7%). Under load-carriage conditions, women had a larger flexion angle at the hip (17.7%–23.5%). In addition, women had a significantly smaller hip extension moment (11.8%–20.0%) and ankle plantarflexion moment (10.2%–14.3%), but larger joint reaction forces (JRFs) at the hip (16.1%–22.0%), knee (9.1%–14.2%), and ankle (8.2%–12.9%). Consequently, we found that women had a greater increase in tibial strain and SF risk than men as load increases, indicating higher susceptibility to injuries. When load carriage increased from 0.0 kg to 22.7 kg, SF risk increased by about 250% in women but only 133% in men. These results provide quantitative evidence to support the Army’s new training and testing doctrine, as it shifts to a more personalized approach that shall account for sex and individual differences.