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doi: 10.1249/JSR.0000000000000045
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Latest Clinical Research Published by ACSM

Jaworski, Carrie A. MD, FACSM, FAAFP

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Address for correspondence: Carrie A. Jaworski, MD, FACSM, FAAFP, Division of Sports Medicine, Department of Family Medicine, University of Chicago/NorthShore University Health System, Glenview, IL 60026; E-mail: CJaworski@northshore.org.

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Effect of Acute Exercise on Clinically Measured Reaction Time in Collegiate Athletes

In the March 2014 issue of Medicine & Science in Sports & Exercise®, researchers investigated the effect of exercise on the reaction times of collegiate athletes using a clinically validated tool to measure reaction time (RTclin) (2). The purpose of the study was to determine the effect of exercise on RTclin in order to understand this tool’s utility as a sideline concussion assessment tool. Pilot work has demonstrated already the reliability and validity of RTclin as well as its sensitivity to concussion in the days following an injury. The authors hypothesized that RTclin would decrease with exercise of moderate intensity and increase with more intense levels of exercise.

In this study, 42 male and female division I collegiate athletes (50% women) without concussions were assigned to either an exercise or control group. The exercise group completed a graded four-stage exercise protocol on a stationary bike while the control group underwent testing at identical periods without exercising. RTclin was defined as the fall time of a vertically suspended rigid shaft after its release by the examiner before being caught by the athlete. The mean RTclin was calculated from eight trials, and the RTclin was measured at baseline and after each of the four stages. The researchers attempted to account for the practice effect and had the athletes do two practice catches prior to the actual study to “washout” any learning effect. The results demonstrated no significant difference between the exercise and control groups as well as no difference between the exercise stages. There was an overall decline during repeated test administration for both groups, and the male athletes had significantly faster RTclin than the female athletes. The authors concluded that exercise did not appear to affect RTclin performance in this particular study. They acknowledged that no direct measurements of aerobic versus anaerobic metabolism were taken despite the intention that the final stage of the exercise test would be anaerobic, so it cannot be stated whether anaerobic exercise affects the RTclin.

Bottom Line: RTclin does not need to be adjusted to account for the acute effects of exercise and may be a worthwhile tool to consider in the sideline assessment of the concussed athlete.

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Increasing Step Rate Reduces Patellofemoral Joint Forces

Increasing step rate while running has been shown to change joint kinematics and kinetics and has been proposed as a rehabilitation strategy for runners with patellofemoral knee pain. Researchers in this study published in the March 2014 issue of Medicine & Science in Sports & Exercise® sought to determine how altering step rate affects internal muscle forces and patellofemoral joint loads in order to then determine which kinematic and kinetic forces best predict changes in joint loading (1). Whole body kinematics was recorded on 30 healthy adults while running on an instrumented treadmill at 3 step rate conditions (90%, 100%, and 110% of preferred step rate). Estimations of muscle, patellar tendon, and patellofemoral joint forces throughout the running gait cycles were made using a 3D lower extremity musculoskeletal model. In addition, the authors used linear regression analysis to determine the relative influence of limb posture and external loads on patellofemoral joint force.

The results of this study demonstrated that increasing one’s step rate to 110% of their preferred rate reduced peak patellofemoral joint force by 14%. Peak muscle forces also were affected by the increased step rate with hip, knee, and ankle extensor forces as well as hip abductor forces all reduced in midstance. Conversely there was an increase in peak rectus femoris and hamstring loads during early and late swing at higher step rates. Peak stance phase knee flexion decreased with an increased step rate and was found to be the most important predictor of the reduction in patellofemoral joint loading. The authors concluded that increasing step rate is an effective strategy to reduce patellofemoral joint forces and could be an effective method to modulating the biomechanical factors that contribute to patellofemoral pain.

Bottom Line: Increasing one’s step rate while running has the potential to decrease patellofemoral joint forces and pain.

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References

1. Lenhardt RL, Thelen DG, Wille CM, et al. Increasing running step rate reduces patellofemoral joint forces. Med. Sci. Sports Exerc. 2014; 46: 557–64.

2. Reddy S, Eckner JT, Kutcher JS. Effect of acute exercise on clinically measured reaction time in collegiate athletes. Med. Sci. Sports Exerc. 2014; 46: 429–34.

Copyright © 2014 by the American College of Sports Medicine.

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