This study evaluated the effect of age on susceptibility to muscular weakness and damage caused by eccentric (ECC) exercise and determined whether this susceptibility was altered by resistance training. Young and older women performed concentric (CON) and ECC one repetition maximum (1 RM) strength tests of the quadriceps femoris. Older women also performed knee extension training for 12 weeks. An unaccustomed bout of ECC knee extension exercise was performed before and after training, and CON and ECC 1 RM were reassessed for 11 days after the ECC bout. Magnetic resonance imaging was used to evaluate changes in muscle water content associated with muscle damage. Before training, older subjects showed a larger decline in CON (p =.008) and ECC (p =.03) strength induced by the unaccustomed ECC bout, compared with the young subjects. One day following the ECC bout, the older women showed a 24% reduction in CON and a 27% reduction in ECC 1 RM, compared with only 6% (CON) and 10% (ECC) in the younger women. A magnetic resonance imaging evaluation indicated that edema or damage was significantly greater in the older untrained women than it was in young women (p <.05), but the resistance-trained older women showed no greater muscle injury than the young women (p >.05). Resistance-trained older women showed no greater decline than sedentary young women in either CON (p >.05) or ECC (p >.05) strength. In conclusion, sedentary older women are more susceptible to ECC-induced muscle dysfunction, but resistance training reduces this susceptibility.

Muscle functional MRI can be used to characterize lumbar muscle function during trunk extension exercise. The levels and recruitment patterns of the lumbar extensors, as measured by muscle T2 shifts, vary with exercise intensity. Future research is needed to assess the mechanism of the nonlinear relationship between T2 shifts and exercise intensity, and to clarify the effects of fatigue and the order of exercise presentation on the T2 response of the lumbar extensors.

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Muscle functional magnetic resonance imaging (mfMRI) has been widely used to study muscle recruitment in exercise in young healthy subjects, but has not been validated or used with older subjects. This study validates and demonstrates the use of mfMRI in older subjects. Subjects consisted of apparently healthy sedentary younger (n = 7) and older (n = 6) women. Proton transverse relaxation (T2)-weighted MRI scans were obtained of the quadriceps femoris at rest and immediately following three bouts of knee extension exercise (50%, 75%, and 100% of untrained 5 x 10 repetition maximum [RM]). Older subjects performed knee extension training for 12 weeks and repeated the MRI scan protocol using the same absolute loads. Training induced a 13% increase in 1 RM and a 25% increase in 5 x 10 RM. Older subjects had higher resting T2 values compared with younger subjects; however, the T2 response to exercise (slope) was similar among groups (young = 0.063+/-0.003, older untrained = 0.055+/-0.011, older trained = 0.053+/-0.008; p > .05). In all cases, T2 increased linearly with load. Trained older subjects showed a lower T2 response when lifting the same absolute load compared with before training, which is consistent with results previously obtained from young subjects. In the older population, mfMRI is appropriate for use and offers benefits over other technologies.

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