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Vulnerability to dysfunction and muscle injury after unloading.

Abstract：

OBJECTIVE:To test whether unloading increases vulnerability to eccentric exercise-induced dysfunction and muscle injury. DESIGN:Before-after trial. SETTING:General community. PATIENTS OR OTHER PARTICIPANTS:Two women and 5 men (73 +/- 3kg [mean +/- SE]) who were active college students but were not trained in lower body resistance exercise volunteered. INTERVENTION: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. MAIN OUTCOME MEASURE(S):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). CONCLUSION:Unloading increases vulnerability to eccentric exercise-induced dysfunction and muscle injury, even at relatively light loads.

journal_name

Arch Phys Med Rehabil

journal_title

Archives of physical medicine and rehabilitation

authors

Ploutz-Snyder LL,Tesch PA,Hather BM,Dudley GA

doi

10.1016/s0003-9993(96)90255-5

subject

Has Abstract

pub_date

1996-08-01 00:00:00

pages

773-7

issue

eissn

0003-9993

issn

1532-821X

pii

S0003-9993(96)90255-5

journal_volume

pub_type

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Vulnerability to dysfunction and muscle injury after unloading.