D-34 Free Communication/Poster- Muscle 4: MAY 29, 2008 1:00 PM- 6:00 PM: ROOM: Hall B
Investigations into the effects of old age on skeletal muscle fatigue have produced conflicting results; some suggest greater fatigability while others suggest fatigue resistance in elderly compared to young adults.
PURPOSE: To test the hypothesis that age-related fatigue resistance in the knee extensor muscles is related to contraction mode.
METHODS: Healthy, untrained young (Y, age 21-33, n=16, 8 male) and older (O, age 65-80, n=16, 8 male) adults were studied. Subjects performed intermittent maximal isometric (5s duration, 50% duty cycle) and isokinetic (.5s, 25% duty cycle; 120 deg·s-1) knee extensions for 4 min. Fatigue was expressed as the relative decline in force from baseline to the average of the final 3 contractions of the isometric, and final 5 contractions of the isokinetic protocol. Habitual physical activity level (PA) was determined by accelerometry for 5 days (mean counts·day-1). Preliminary analysis detected no gender effect, so data were collapsed by gender and analyzed using a oneway ANOVA. Group means were compared via unpaired T-test.
RESULTS: O and Y were well matched for PA (191,131.4 ± 21722.6 vs. 197,165.6 ± 18970.3 respectively (p=0.91)) Fatigue differences were detected in the isometric protocol, with O having less fatigue than Y (31.5 ± 2.9% vs. 45.1 ± 3.3% respectively; p = 0.006). In contrast, during the isokinetic protocol, no differences between groups were detected between O and Y (56.8 ± 3.5% vs. 56.24 ± 3.2% respectively; p=0.903).
CONCLUSIONS: In activity-matched young and older adults, age-related fatigue resistance in the knee extensors depends on contraction mode, with the greater fatigue resistance of the old observed during isometric contractions being abolished during dynamic contractions. These results contribute to the emerging picture of the factors influencing muscle fatigue under various conditions in aging humans.
Support: NIH R01 AG21094, NIH K02 AG023582