K. J. Eustis, S. O. Henry

Pacific University, Forest Grove, OR

In healthy individuals, pain sensation has been shown to decrease after a bout of moderate-to-vigorous exercise, a phenomenon termed exercise-induced hypoalgesia (EIH). However, it is unclear if aerobic fitness level influences EIH. PURPOSE: Firstly, determine if 10 minutes of cycling at 50% intensity is sufficient perturbation to induce EIH. Secondly, investigate the relationship between aerobic fitness level and EIH magnitude. METHODS: Using within-subjects design, 34 healthy adults (age = 20.8 ± 1.4 yrs, 21 female, 13 male) completed a Forestry Step Test to estimate VO2max, followed by 10 minutes of stationary cycling. The cycle ergometer workload (W) was scaled to individual fitness level, using 50% VO2max translated into watts. Estimated VO2max for subjects ranged from 31 to 61 ml·kg-1·min-1 (mean = 47.18 ± 9.25 ml·kg-1·min-1). Pain sensation was measured via pressure-pain threshold test (PPT) pre- and post-exercise. Using a digital dolorimeter, incrementally increasing pressure (kg·cm-1) was applied in repeated measures on either forearm or quadriceps, with the pressure recorded when the subject reached their perceived pain threshold. Forearm represented the non-exercised site whereas quadriceps represented the directly-exercised site. Dependent t-tests analyzed differences between pre- and post-exercise PPT values, determining if EIH was induced. Pearson correlation described the relationship between the magnitude of EIH and est. VO2max. RESULTS: Exercise did not induce EIH at the forearm site, with no difference between pre-exercise and post-exercise PPT (2.89 ± 1.43, 3.02 ± 1.51 kg·cm-1 respectively). However, EIH was induced at the quadriceps site (PPT pre = 3.87 ± 2.17, post = 4.42 ± 2.50 kg·cm-1; t33 = -4.306, p<0.001). Magnitude of quadriceps EIH (pre-post PPT difference) showed a moderate positive correlation with estimated VO2max (r = 0.447, p = 0.008). CONCLUSION: Although the exercise protocol did not induce EIH in the non-exercised area (forearm), it successfully induced EIH in the local musculature (quadriceps). Most importantly, aerobic fitness, as represented by estimated VO2max, was shown to modestly influence EIH. Higher aerobic fitness was positively associated with increased magnitude of EIH.

Supported by a grant from Pacific University College of Arts & Sciences.

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