Muscle proton T2 relaxation times and work during repetitive maximal voluntary exercise.
We studied the effects of progressive maximal voluntary handgrip contractions (MVCs) on muscle proton spin-spin (T2) relaxation times and work, measured as the integrated force vs. time curve (FTI). Six healthy volunteers performed 10, 20, 40, and 80 MVCs in a 0.35-T magnet on four separate occasions. Repeated measures analyses of variance of increases in T2 and FTI during successive bouts were significant (P < 0.005 and P < 0.001, respectively). FTI increased with successive bouts to a greater extent than did muscle T2 (P < 0.05). For T2, the Helmert contrast judged the 10-MVC response lower than the mean of the remaining responses (P < 0.005), and the differences between all others compared with the means of subsequent responses were not significant, indicating a "flattening" of the T2 response after the increase from 10 to 20 repetitions. For FTI, all the single degree of freedom Helmert contrasts were significant (P < 0.001), indicating a continual increase in response over increased MVCs. The curved nature of the T2 response conformed best to a hyperbolic function, suggesting that a limit of approximately 32% exists for the change in T2 during progressively longer bouts of MVCs. A limit in the T2 response is consistent with the existence of a limit in the amount of water that muscle can take up from the vasculature during exertion.
Fleckenstein
J L
JL
Department of Radiology, University of Texas Southwestern Medical Center, Dallas 75235.
Watumull
D
D
McIntire
D D
DD
Bertocci
L A
LA
Chason
D P
DP
Peshock
R M
RM
D000328:Adult; D001834:Body Water / Q000378:metabolism; D015444:Exercise / Q000502:physiology*; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D008279:Magnetic Resonance Imaging; D009132:Muscles / Q000033:anatomy & histology / Q000502:physiology*; D011522:Protons
D011522:Protons