Changes in muscle proton transverse relaxation times and acidosis
during exercise and recovery.
Cheng, H. A., R. A. Robergs, J. P. Letellier, A. Caprihan, M. V.
Icenogle, and L. J. Haseler.
The Lovelace Institutes: Institute for Basic and Applied Medical
Research, 2425 Ridgecrest Drive, S.E., Albuquerque, NM 87108,
APStracts 2:0212A, 1995.
We studied changes in muscle proton (1H) transverse relaxation times
(T2) by magnetic resonance imaging (MRI) during exercise, and
compared these changes with alterations in muscle metabolism measured
by phosphorous magnetic resonance spectroscopy (31P MRS). Eleven
subjects completed two trials of intermittent incremental forearm
wrist flexion exercise requiring 30 contractions/min for 5 min, 7 min
of recovery between stages, and 5 N load increments per stage.
Between stages of the first trial, T2 images of muscle 1H were
obtained. Muscle T2 increased from 27.3+1.1 ms (M+SD) at rest, to
35.8+3.6 ms following volitional fatigue (p<0.05), whereas less
active wrist extensor muscle T2 remained unchanged (26.8+0.9 to
28.8+1.6 ms, p>0.05). After localizing the predominant muscle
recruited from the T2 images, subjects completed an identical trial
at least one week later, but involving surface coil 31P MRS of the T2
enhanced muscle to measure [H+]. Intramuscular [H+] of T2 enhancing
muscle increased from 1.1+0.1 Mx10-7 at rest to 4.1+2.0 Mx10-7
following volitional fatigue. Both muscle T2 and intramuscular [H+]
increased in a bimodal manner, with T2 increasing prior to muscle
[H+] (p<0.05). The correlation coefficient between the percent
change in T2 and muscle [H+] during exercise was +0.74 (p<0.05)
(range: r=0.48 to 0.98), and +0.47 during recovery. After 12 min of
recovery, muscle [H+] decreased to 1.4+0.3 Mx10-7 (p<0.05), and T2
remained close to post-exercise values (32.2+3.1 ms, p>0.05). The
data indicate that 1) the T2 increases during increases in exercise
intensity are non-linear, 2) T2 increases during exercise are
significantly correlated with increases in [H+], and 3) the slow
recovery of T2 compared to [H+] indicates that [H+] has a minor
contribution to the recovery in T2.
Received 4 August 1994; accepted in final form 16 May 1995.
APS Manuscript Number A804-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 May 1995.