EFFECTS OF A 2-HOUR RUN ON METABOLIC ECONOMY AND LOWER-EXTREMITY STRENGTH IN MEN AND WOMEN

Changes in running economy, or the oxygen cost of running at a given s ubmaximal speed (ml/m/kg), during prolonged exercise have been well de scribed in men but not in women, lower extremity strength changes asso ciated with prolonged exercise have never been addressed. We examined changes in running economy and strength following a 2-hour run in eigh t men and eight women. Knee and hip strength were measured pre-and pos t-running. Peak oxygen consumption (VO2peak) and oxygen consumption at ventilatory threshold were determined. Subjects then ran for 2 hours at an intensity which elicited ventilatory threshold (68.7% vs. 66.6% of VO2peak for men and women, p = 0.5). Water was ingested al a rate o f 0.5% of body weight each half hour. Oxygen uptake (VO2) and respirat ory exchange ratio were measured initially and at 1 and 2 hours. Body weight declined in the men (p = 0.001) but not in the women (p = 0.12) . Running economy decreased in the men (p < 0.001) but not in the wome n (p = 0.084). At 2 hours of running, knee flexion and extension stren gth declined significantly in the men only (effect of gender x time, p < 0.074), but hip flexion, abduction, and adduction strength declined in both genders. Decreased knee extensor/flexor strength was evident in men only, while decreased hip strength was independent of gender. W e conclude that 2 hours of running produced changes in knee strength a nd running economy in men only.