Gary Helton, Kenneth L. Cameron, Rebecca A. Zifchock, Erin Miller, Donald Goss, Jinsup Song, and Michael Neary
PURPOSE: Prospectively investigate the relationship between running shoe characteristics and lower extremity musculoskeletal injury. METHODS: The study included 1025 of 1308 incoming United States Military Academy (USMA) cadets. Shoe length and stiffness were recorded to calculate shoe torsional stiffness while shoe heel height was also recorded. Demographic data and Army Physical Fitness Test (APFT) data were also recorded. Lower extremity injuries sustained over nine weeks during cadet basic training were documented using the Armed Forces Health Longitudinal Technology Application (AHLTA) and the Cadet Illness and Injury Tracking System (CIITS). Kaplan-Meier survival curves were estimated with time to incident of lower extremity injury as the primary outcome by level of the independent predictor variables. Risk factors and known or potential covariates were carried forward into multivariable Cox Proportional Hazards Regression Models. RESULTS: Approximately 18.1% of participants incurred a lower extremity injury. Cadets wearing shoes with moderate lateral torsional stiffness were 49% less likely to incur any type of lower extremity injury and 52% less likely to incur a lower extremity injury due to overuse than cadets wearing shoes with minimal lateral torsional stiffness. Risk of injury was similar among cadets wearing shoes with minimal and extreme lateral torsional stiffness. CONCLUSIONS: Shoes with mild to moderate lateral torsional stiffness may be appropriate in reducing risk of lower extremity injury in cadets. Shoes with minimal lateral torsional stiffness should be discouraged in this population.
Effects of a Loaded Ruck March of Isometric Muscle Strength Measured with a Novel HHD Fixation System
Jessica Schindler, Jonathan Kaplan, Clifford Hancock, Erika Hussey, Rebecca A. Zifchock, and John Ramsay
PURPOSE: Understanding the effect that field exercises have on soldier muscular strength is an area of interest for the US Army. Reliably quantifying muscle strength in this context has been limited by availability of portable assessment equipment. The widely used hand-held dynamometer (HHD) presents a challenge when assessing strong muscle groups of healthy soldiers accurately. We devised a portable, field-ready HHD fixation solution to assist researchers in the evaluation of lower body and core isometric maximal muscle contractions. Reliability of the fixation system (patent pending) was assessed prior to implementation at a large- scale data collection during a military field exercise. The purpose of the current investigation was to identify strength changes in select muscle groups prior to and immediately following a loaded road march.
METHODS: 39 soldiers (36M, 3F) performed 4 maximal isometric contraction types, including lumbar extension, lumbar flexion, hip flexion, and knee extension. 3 trials of each contraction type were recorded during a pre-mission baseline, and 2 trials were recorded immediately following a 6-mi road march executed with an average load of 50% body weight. Measurements were recorded using the system developed, which provided repeatable subject stabilization, muscle group isolation, and HHD fixation.
The maximum force recorded from each muscle group during a session was used for analysis. A paired sample t-test was conducted to compare pre and post road march strength measures.
RESULTS: No significant change in lumbar extension strength was identified between the pre and post conditions. Significant decreases in strength performance were observed in the hip flexion (8.3%; p=.003), knee extension (7.8%; p=.032), and lumbar flexion (9.9%; p=.009) measurements between the pre and post conditions.
CONCLUSION: While lumbar extension strength did not change following the road march, the decreases identified for hip flexion, knee extension, and lumbar flexion followed the hypothesized trend. This study provides novel insight into the effects of field activities on soldier muscle strength that were not quantifiable prior to the portable HDD fixation system, and presents a range of new opportunities to understand the impact of military exercises on strength.
Joseph Drennan, Matthew Vest, Gabriela Barrera, Tyler Weaver, Logan Leahy, and Rebecca A. Zifchock
Effects of Torso-Borne Load Redistribution on Comfort and Gait Mechanics.
Ruth Talbott, Rebecca A. Zifchock, Roderick Wilson, and William Blackmon
Examination of the Linearity and Eversion/Inversion Symmetry of Torsional Stiffness in Footwear.
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