Interval Training Is Not Superior to Endurance Training With Respect to Bone Accrual of Ovariectomized Mice.

Physical exercise is considered to delay bone loss associated with post-menopausal estrogen deficiency in women. However, the optimal training regimen for maximal bone accrual has not yet been defined. We, therefore, turned to ovariectomized (OVX) C57BL/6 mice and directly compared a low intensity endurance training on the treadmill to medium and high intensity interval trainings tailored to the individual performance limits. Trainings lasted 30 min each and were performed five times/week. After a 5-week training period, mice were sacrificed, and the hind legs were analyzed for assessment of (i) biomechanical stability (three-point bending test), (ii) bone microarchitecture [micro-computed tomography (µCT)], (iii) mineral apposition rate (MAR; histomorphometry), and (iv) muscle volume (MRI). Increased running speeds and quadriceps femoris muscle volumes in trained mice confirmed positive impacts on the cardiopulmonary system and myoinduction; however, none of the treadmill training regimens prevented ovariectomy induced bone loss. Our results provide evidence that treadmill training impacts differentially on the various members of the musculoskeletal unit and call for further experiments investigating frequency and duration of training regimens.

Young and healthy C57BL/6 J mice performing sprint interval training reveal gender- and site-specific changes to the cortical bone.

Physical exercise is considered to impede the bone loss associated with physiological ageing however, a training program that efficiently leads to bone accrual in the healthy does not yet exist. We turned to the C57BL/6 J mouse and designed a sprint interval training for treadmill that was tailored to the individual performance limits. It consisted of four weeks with five training sessions each, followed by another four weeks with three. After completion of the training period, mice were sacrificed and the hind legs were analyzed via µCT and MRI for changes in bone parameters and muscle volume, respectively. Increased performance limits in both sexes confirmed an effect of the treadmill training. However, while male tibiae after eight weeks revealed a significant reduction of cortical bone mass at the distal metaphysis, the cross sectional analysis of female tibiae showed a transient decrease of cortical bone mass after four weeks that was reversed into a significant accrual after eight weeks of training and occurred over the entire length of the tibia. The observed net reduction of female bone mass after four weeks of training is suggestive of a remodelling process which may be delayed in the males.