Vulnerability to dysfunction and muscle injury after unloading.
OBJECTIVE
To test whether unloading increases vulnerability to eccentric exercise-induced dysfunction and muscle injury.


METHODS
Before-after trial.


METHODS
General community.


METHODS
Two women and 5 men (73 +/- 3kg [mean +/- SE]) who were active college students but were not trained in lower body resistance exercise volunteered.


METHODS
Five weeks of unilateral lower limb suspension (ULLS), which has been shown to decrease strength and size of the unloaded, left, but not load-bearing, right quadriceps femoris muscle group (QF) by 20% and 14%, respectively; performance of 10 sets of ten eccentric actions with each QF immediately after the ULLS strength tests with a load equivalent to 65% of the post-ULLS eccentric 1-repetition maximum.


METHODS
Concentric and eccentric 1-repetition maximum for the left, unloaded and the right, load-bearing QF measured immediately after ULLS and 1,4,7,9, and 11 days later; cross-sectional area and spin-spin relaxation time (T2) of each QF as determined by magnetic resonance imaging and measured the last day of ULLS and 3 days later.


RESULTS
The mean load used for eccentric exercise was 23 +/- 2 and 30 +/- 3kg for the left, unloaded and right, load-bearing QF, respectively. The concentric and eccentric 1-repetition maximum for the unloaded and already weakened left QF was further decreased by 18% (p = .000) and 27% (p = .000), respectively, 1 day after eccentric exercise. Strength did not return to post-ULLS levels until 7 days of recovery. The right, load-bearing QF showed a 4% decrease (p = .002) in the eccentric 1-repetition maximum 1 day after eccentric exercise. The left, unloaded QF showed an increase in T2 (p = .002) in 18% of its cross-sectional area 3 days after the eccentric exercise, thus indicating muscle injury. The right, load-bearing QF showed no elevation in T2 (p = .280).


CONCLUSIONS
Unloading increases vulnerability to eccentric exercise-induced dysfunction and muscle injury, even at relatively light loads.
Ploutz-Snyder
L L
LL
Department of Biological Science, Ohio University, Athens, USA.
Tesch
P A
PA
Hather
B M
BM
Dudley
G A
GA
D000328:Adult; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D007866:Leg / Q000502:physiology; D008279:Magnetic Resonance Imaging; D008297:Male; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000473:pathology* / Q000502:physiology; D016474:Weight-Bearing