Local and Generalized Endogenous Pain Modulation in Healthy Men: Effects of Exercise and Exercise-Induced Muscle Damage.

Isometric exercise has been shown to activate endogenous pain inhibitory pathways in healthy adults, but not in some clinical pain populations.

OBJECTIVE:  Exercise-induced muscle damage (EIMD) and the associated delayed-onset muscle soreness (DOMS) are a model for studying clinical pain; thus, our purpose was to examine the effects of isometric exercise on pressure pain threshold (PPT) in the presence and absence of DOMS.

METHODS:  Data were collected on 23 males (22.8 ± 2.5 yrs). PPT was assessed in the right (exercising) and left (resting) quadriceps prior to, every 30 seconds during, and 2 and 15 minutes following an isometric contraction of the right quadriceps at 25% of maximal voluntary contraction (MVC) held until fatigue. Unilateral eccentric exercise was performed to induce DOMS in the exercising leg and testing was repeated 48 hours later.

RESULTS:  DOMS increased (P < 0.001) and resting PPT decreased (P = 0.03) following EIMD. PPTs were elevated during exercise in the exercising (P ≤ 0.002) and resting (P ≤ 0.002) quadriceps but did not differ between the control and EIMD conditions in either leg (P ≤ 0.61). PPT remained elevated 2 and 15 minutes postexercise (P < 0.05) in the exercised quadriceps in both conditions, but values returned to baseline at 2 (P = 0.91) and 15 minutes (P = 0.28) postisometric exercise in the resting quadriceps.

CONCLUSIONS:  Unlike clinical pain, DOMS had no effect on the PPT response during exercise in either the exercising or resting quadriceps. The fact that exercise altered PPT in both quadriceps during exercise suggests a generalized pain inhibitory mechanism was activated. However, the restriction of postexercise effects to the exercised limb suggests localized inhibitory mechanism(s) were activated after exercise.