The effect of fatigue on ground reaction force asymmetries in jumps and hops
Date
2018
Authors
Patrick, Ryan, author
Reiser, Raoul F., II, advisor
Tracy, Brian L., committee member
Rosecrance, John C., committee member
Journal Title
Journal ISSN
Volume Title
Abstract
INTRODUCTION: Functional movement assessments (FMAs) have gained popularity for screening athletes to determine deficits in movement quality that could increase the risk for injury. Several multi-component FMAs exist, but few use demanding jump tasks for assessment. The two-legged countermovement jump (CMJ) and the single-leg hop (SLH) for distance have been common clinical FMAs to assess for levels of asymmetries in athletes due to their ease of application and similarity to sport play. Injuries occur at greater rates when athletes are fatigued, yet FMAs are often administered when they are fresh. It possible that fatigue and asymmetries interact to increase the injury risk in athletes during athletic tasks. PURPOSE: The goal of this investigation was to analyze the vertical ground reaction forces (GRFv) in the CMJ and SLH and the anterior-posterior GRF (GRFap) in the single-leg landing in young, healthy, recreationally active men and women. It was hypothesized small asymmetries would exist in pre fatigue measures and would decrease in the CMJ as a result of fatigue, but that there would be increases in asymmetry in the SLH landing. Lastly, these measures would be highly repeatable day-to-day. METHODS: Seventeen injury free and recreationally trained subjects (9 men, 8 women) (mean ± SD age: 22.3 ± 2.5 yrs; height 170 ± 9.3 cm; mass 73.4 ± 13.8 kg) performed five maximum effort CMJ pausing to reset one foot on each force platform before performing subsequent jumps. Following this subjects performed three single-leg hops from one force platform to another over a distance of 50 cm (20 in) and make a stable landing. Subjects performed a fatiguing protocol that involved five sets of eight repetitions with 90% of their predetermined eight-repetition maximum (8RM 113 ± 35 % of their body mass). Following fatigue, the subjects repeated the CMJ and SLH landing protocols. The results of the five CMJ were averaged and GRF data on each limb was divided by the total to assess asymmetries in GRFv average and maximum pre and post fatigue. The average of three SLH for each limb was averaged and divided by bodyweight to normalize asymmetries. Eight subjects were reassessed for repeatability measures. RESULTS: There was evidence of initial asymmetries in the CMJ and SLH landing. The fatigue protocol was validated by a significant reduction in jump height (p<0.001), but there were no significant changes in the relative (L-R%) levels of GRFv asymmetries for average (p=0.437) or maximum (p=0.294). Absolute changes to GRFv asymmetry (|L-R%|) are used to detect the magnitude of asymmetry change that may be lost in side-to-side averages. Absolute GRFv average (|L-R%|) and absolute GRFv maximum (|L-R%|) did not reach statistical significance (p=0.705 and p=0.983, respectively), indicating that the levels of asymmetry in the CMJ was unchanged by fatigue. Only one measure in the SLH landing reached statistical significance, absolute GRFv maximum (|L-R%|) (p=0.031). The CMJ was highly repeatable day-to-day and only two measures had acceptable repeatability in the SLH landing: GRFv maximum pre fatigue (L-R%) (⍺=0.746) and GRFv average post fatigue (⍺=0.665). CONCLUSION: These results suggest that functional asymmetries, though low, were present and remained constant with fatigue in the CMJ. Absolute GRFv maximum (|L-R%|) was the only SLH variable that supported the hypothesis. All other measures did not increase as expected. The CMJ was highly repeatable, but measures in the SLH were not. Repeatable and reliable assessments are important for detecting injury risk in athletes prior to starting a season or returning from injury. Future research is needed to determine the most valuable FMAs for detecting asymmetries and in populations that have higher rates of asymmetry.