No abstract

Ten young male adults (mean age 46.9 +/- 1.2 yrs) with 9.2 +/- 1.4 years of weight training experience and the ability to parallel squat at least 1.5 times their body mass were selected as subjects. The exercise session consisted of sets of 10 repetitions at 65% 1-RM of the parallel leg squat, with a cadence of one rep every 6 sec and 3 min rest between sets, to muscular failure. The average subject lifted a total of 9711 +/- 1576 kg during 98 +/- 14 reps for a total work output of 72.5 +/- 10.5 kJ before muscular failure occurred. Mean oxygen consumption during exercise was 1.58 +/- 0.06 l/min at 42.5 +/- 2.0% peak VO2. A strong leukocytosis, lymphocytosis, and lymphocytopenia, similar to what has been reported following high-intensity cardiorespiratory exercise, were measured following leg squat exercise. Con A-stimulated lymphocyte proliferation (unadjusted) rose 50% above preexercise levels (p = 0.07), but when these data were adjusted on a per T cell (CD3+) basis, no change from rest was observed. Natural killer cell cytotoxic activity (NKCA), when adjusted on a per NK cell (CD56+) basis, was decreased about 40% below preexercise levels for at least 2 h post-exercise. No significant increase in cortisol was seen after exercise, although norepinephrine and epinephrine increased moderately (465% and 133%, respectively), immediately following exercise. The data demonstrate that leg squat exercise to muscular failure results in a very similar immune response to that associated with intense endurance exercise, despite a lower mean oxygen consumption and only a moderate hormonal response.

No abstract

This study investigated changes in skeletal muscle cross-sectional area (CSA) evoked by fluid shifts that accompany short-term 6 degrees head-down tilt (HDT) or horizontal bed rest, the time course of the resolution of these changes after resumption of upright posture, and the effect of altered muscle CSA, in the absence of increased contractile activity, on proton transverse relaxation time (T2). Average muscle (CSA and T2 were determined by standard spin-echo magnetic resonance imaging. Analyses were performed on contiguous transaxial images of the neck and calf. After a day of normal activity, 24 h of HDT increased neck muscle CSA 19 +/- 4(SE)% (P < 0.05) while calf muscle CSA decreased 14 +/- 3% (P < 0.05). The horizontal posture (12 h) induced about one-half of these responses: an 11 +/- 2% (P < 0.05) in the neck muscle CSA and an 8 +/- 2% decrease (P < 0.05) in the calf. Within 2 h after resumption of upright posture, neck and calf muscle CSA returned to within 0.5% (P > 0.05) of the values assessed after a day of normal activity, with most of the change occurring within the first 30 min. No further change in muscle CSA was observed through 6 h of upright posture. Despite these large alterations in muscle CSA, T2 was not altered by more than 1.1 +/- 0.6% (P > 0.05) and did not relate to muscle size. These results suggest that postural manipulations and subsequent fluid shifts modeling micro-gravity elicit marked changes in muscle size. Because these responses were not associated with alterations in muscle T2, it does not appear that simple movement of water into muscle can explain the contrast shift observed after exercise.