A methionine-restricted diet and endurance exercise decrease bone mass and extrinsic strength but increase intrinsic strength in growing male rats.

Dietary methionine restriction (MR) has been suggested to be comparable to endurance exercise with respect to its beneficial effects on health. To further investigate the effects of MR and endurance exercise on growing bone, 7-wk-old male Sprague-Dawley rats were fed different l-methionine (Met)-containing diets with or without endurance exercise intervention (Ex; 0.86% Met, 0.52% Met, 0.17% Met, 0.86% Met-Ex, 0.52% Met-Ex, and 0.17% Met-Ex groups). After an 8-wk intervention period, exercise-trained rats had a 9.2% lower body weight (BW) than did sedentary rats (P < 0.05). Additionally, 0.17% Met-fed rats had 32% lower BW when compared with rats fed the other 2 diets (P < 0.05). Serum osteocalcin was lower in the 0.17% Met-Ex group compared with the other 2 exercise groups and the 0.17% Met group (P < 0.05). Serum concentrations of C-terminal telopeptide of type 1 collagen were lower in exercise-trained and 0.17% Met-fed rats than in sedentary rats and rats fed the other 2 diets (P < 0.05 for both). Rats fed the 0.17% Met diet had lower trabecular bone volume, bone mineralization activities, and bone mineral content (BMC; e.g., total, cortical, and spongy BMC) and bone mineral density (BMD; e.g., total and spongy BMD) indices compared with rats fed the other 2 diets (P < 0.05). Exercise-trained rats also had lower bone mineralization activity, trabecular osteoclast density, total BMC, cortical BMC, and total BMD compared with sedentary rats (P < 0.05). In total BMD, only the 0.17% Met-Ex group had values lower than the other 2 exercise groups and the 0.17% Met group (P < 0.05). Compared with rats fed the other 2 diets and sedentary rats, the femora of 0.17% Met-fed and exercise-trained rats, respectively, had smaller size and/or lower extrinsic strength but enhanced intrinsic biomechanical properties (P < 0.05). The results indicate that MR and endurance exercise caused lower whole bone mass, size, and/or strength but might enhance intrinsic bone strength.

Short-term free-fall landing causes reduced bone size and bending energy in femora of growing rats.

The purpose of this study was to determine the effects of a mechanical loading course (short-term free-fall landing) on femoral geometry and biomechanical properties in growing rats. Thirty-two female Wistar rats (7-week-old) were randomly assigned to three groups: L30 (n = 11), L10 (n = 11) and CON (n = 10) groups. Animals in the L10 and L30 groups were subjected to a 5-day free-fall landing program in which animals were dropped from a height of 40cm 10 and 30 times per day, respectively. Landing ground reaction force (GRF) was measured on the 1(st) and 5(th) days of landing training. All animals were subjected to two fluorescent labeling injections on the days before and after the 5-day landing training. Three days after the last labeling injection, animals were sacrificed under deep anesthesia. Methods of dynamic histomorphometry, tissue geometry and tissue biomechanical measurements were used to investigate the response in femora. A significant decrease in peak GRF in the hind-limb was shown from day 1 to day 5. No significant difference was shown among groups in dynamic histomorphometry. Biomechanical property analyses showed significantly lower maximal energy and post-yield energy in the L10 and L30 groups as compared to the CON group (p < 0.05). Moreover, geometric measurements revealed that cross-sectional cortical areas and thicknesses were significantly lower in landing groups than in the CON group. Short-term (5-day) free-fall landing training resulted in minor compromised long bone tissue, as shown by reduced bending energy and cortical bone area but not in other mechanical properties or tissue measurements (e.g. weights and length) of growing female rats. Further studies would be valuable to investigate whether this compromised bone material represents the existence of a latency period in the adaptation of bone material to external mechanical loading. Key pointsShort-term free-fall landing causes compromised bone material as shown by reduced post-yield energy in long bones of rodents.The results of the current study suggest the existence of unsettled bone material after a short-term mechanical loading regime.The connection of the present animal study to the stress fractures occurring in young athletes needs to be clarified.