Does weight-bearing exercise affect non-weight-bearing bone?

It was previously reported that weight-bearing exercise increases femur periosteal formation in 3-year-old, 230 kg cross-bred sows. To determine if this weight-bearing exercise also stimulated non-weight-bearing bone, bone formation in the seventh rib from these same sows was measured histomorphometrically on the periosteal, endocortical, and osteonal envelopes. The sows were randomly assigned by body weight to basal (B, n = 6), control (C, n = 7), or trained (T, n = 7) groups. After 3 weeks of exercise adaptation, T walked on a treadmill for 17 weeks at 5 km/h, 20 minutes/day, 5 days/week, at 5% grade. Groups were sacrificed initially (B) or after 20 weeks (C and T). Periosteal mineral apposition rate (MAR) was calculated over 136 days. Osteonal and endocortical MAR were calculated over the 14 days prior to sacrifice. There were no effects of exercise on the periosteal or endocortical percentage double-labeled surface (dLS/BS), osteonal remodeling frequency (N.dL.On/B.Ar), or MAR in any bone envelope of the rib. In conclusion, weight-bearing exercise sufficient to stimulate periosteal formation in the femur did not activate formation in the rib. Bone response to weight-bearing exercise appears to be specific to the loaded bones.

Body composition, muscle and fat pad changes following two levels of dietary restriction and/or exercise training in male rats.

This study examined the effects of exercise training on conservation of lean mass during moderate and severe dietary restriction in male Sprague-Dawley rats. Eight rats each (48 total) were assigned to one of three levels of dietary restriction (ad lib., AL; moderate, MR; severe, SR) and to one of two activity levels (cage-confined, CC; or treadmill exercised, E) for a 10-week period. Post-intervention, the AL-E (91 percent), MR-CC (84 percent), MR-E (86 percent), SR-CC (66 percent) and SR-E (68 percent) groups all weighed less than the AL-CC group (427 +/- 4.3 g). Exercise training resulted in conservation of lean mass (protein + water + ash) at the moderate but not severe levels of dietary restriction. Further examination showed that this was mostly water since no between-group differences existed at any given diet level for protein or ash mass. Exercise training did elicit conservation of left ventricular heart muscle mass at both the moderate and severe levels of dietary restriction. In contrast, gastrocnemius muscle mass was conserved or maintained only at the moderate dietary restriction level. Thus, the level of dietary restriction appears to affect the ability of exercise training to elicit conservation of both total lean mass and the mass of individual muscles during diet-induced body mass reduction.

Exercise training attenuates diet-induced reduction in metabolic rate.

The combined influence of exercise training and dietary restriction on daily energy expenditure was evaluated by exposing 48 male Sprague-Dawley rats to one of three food intake conditions [ad libitum (AL), moderately restricted (MR), or severely restricted (SR)] and to one of two exercise conditions [treadmill exercised (E) or cage confined (CC)]. After 10 wk of exercise and dietary restriction, the MR-CC and MR-E rats weighed 84 and 86%, respectively, of AL-CC, whereas the SR-CC and SR-E rats weighed 66 and 68% of AL-CC. Dietary restriction and subsequent weight loss produced significant reductions in both total and resting daily energy expenditure. Exercise partially reversed this effect, but the extent of this reversal diminished as the severity of dietary restriction was increased. These results raise the distinct possibility that inconsistencies in the current literature concerning the effects of exercise on whole body metabolism during periods of dietary restriction might be reconciled by an appreciation and an understanding of the influence that duration of exercise training and severity of food restriction have on this measure.

Neither high- nor low-intensity exercise promotes whole-body conservation of protein during severe dietary restrictions.

The effects of 11 weeks of severe dietary restriction alone or in combination with either high- or low-intensity exercise on conservation of protein were studied in 32 male Sprague-Dawley rats. The rats were assigned to one of four groups: sedentary control (C), diet restriction alone (DO) or diet restriction in combination with either high-intensity (HI) or low-intensity (LO) exercise. The groups trained at either 75 percent (HI) or 37.5 percent (LO) of maximal running speed for up to 45 or 90 min/day, 5 days/week, respectively. Total (g) proteins, fat, water and ash content did not differ between the DO, HI and LO groups and were all reduced significantly in comparison to C. Similarly, heart, gastrocnemius muscle and epididymal fat pad masses were significantly reduced for the DO, HI and LO groups in comparison to C. However, the absolute decrease in heart mass was reduced for the HI group (heart mass = 0.31 percent of body mass) in comparison to the DO group (heart mass = 0.28 percent of body mass). Thus, in lean rats undergoing severe dietary restrictions, neither high- nor low-intensity exercise appears to affect total protein conservation in comparison to diet alone. However, high-intensity exercise training appears to attenuate cardiac but not skeletal muscle mass loss in the face of severe dietary restriction.