Strength training (for bone)

Mechanism: bone's mechanotransduction signal

Bone tissue is metabolically dynamic and is continuously remodeled throughout life in response to the mechanical loads it receives; osteocytes (the sensing cells of bone) detect the microscopic deformations induced by muscle contraction forces and by impacts, and trigger signaling cascades that stimulate osteoblasts to deposit new mineralized matrix; high-intensity, low-frequency loads (typical of strength training with significant resistance) are particularly effective as an osteogenic stimulus, more so than low-intensity, high-frequency aerobic exercise (which has other important cardiovascular benefits but a more modest effect on bone).

Clinical evidence: trials in postmenopausal osteoporosis

Multiple randomized trials have shown that progressive strength training performed 2-3 times per week for 6-12 months produces significant improvements in hip and lumbar spine bone mineral density in postmenopausal women with osteopenia or osteoporosis, with magnitudes comparable or superior to some pharmacological interventions; the Australian LIFTMOR trial, published in 2018, showed notable improvements with a protocol of supervised high-intensity strength exercises (squats, deadlifts, and overhead press with progressive resistance), 30 minutes twice a week for 8 months, in postmenopausal women with osteoporosis or osteopenia, with excellent safety and high adherence.

Sarcopenia and fall prevention

In sarcopenia, strength training is the most effective known intervention for preserving and increasing muscle mass in older adults; combined with adequate protein intake (1.2-2.0 g/kg/day from complete sources), it produces significant improvements in strength, muscle mass, balance, and reduced fall risk, one of the main causes of osteoporotic fracture in older adults.

Practical recommendations

International recommendations converge on similar guidelines: 2-3 weekly sessions of strength training with multi-joint exercises (squats, deadlifts, presses, rows, etc.) using significant resistance (60-85 percent of 1-repetition maximum), 8-12 repetitions per set, 2-4 sets per exercise, with sustained progression in loads over time; older or sedentary people should start with professional guidance to learn correct technique before progressing to heavy loads.

How to get started and precautions

For people with no prior experience, starting with professional guidance (certified trainer, physical therapist) to learn correct technique is essential; gym machines make it easier to learn technique before progressing to free weights; bodyweight exercises (squats, push-ups, pull-ups) can be a starting point for people with limited access; older people require more careful progression but can and should reach significant loads to obtain maximum bone benefits.

Generally very safe when performed with proper technique and appropriate progression; the safety considerations are: people with significant cardiovascular disease should have a cardiology evaluation before starting intense strength training; people with established severe osteoporosis or previous fractures should start with professional supervision to avoid contraindicated movements (especially deep spinal flexion under load); people with severe osteoarthritis can adapt exercises to avoid joint pain; in pregnancy, moderate adapted strength training is safe and beneficial under supervision; incorrect technique is the main cause of avoidable injuries, not intensity per se; the reasonable current clinical position is: progressive strength training is probably the non-pharmacological intervention with the best cost-benefit balance for preventing and treating osteoporosis and sarcopenia, and it should be part of standard clinical prescription in adults of all ages, especially in perimenopausal and postmenopausal women and in older adults of both sexes.