Physician's Perspective

Revisiting Our Assumptions of Exercise and Bone Health

Steven R. Gambert, MD, AGSF, MACP Editor-in-Chief, Clinical Geriatrics®

At the 2012 American Geriatrics Society annual meeting, Robin M. Daly, PhD, professor and chair, Exercise and Ageing, School of Exercise and Nutrition Sciences, Melbourne, Australia, spoke about nonpharmacologic interventions for falls and fracture prevention. Daly mentioned a study by Nikander and colleagues1 that reported a 2.3-fold increased risk of fracture in men who walked 3 hours or more per week. This was found even after correcting for age, body mass index, history of fractures, cardiovascular disease, smoking, and use of calcium and vitamin D supplements. No statistical differences were found in fracture risk for women or for those who walked for a shorter period of time. Was it a decline in bone mineral density or a higher risk of falling that caused these men to be at greater risk of fracture with increased walking time? Although it is difficult to derive any conclusions from only hearing a brief synopsis at a meeting, judging by the audience’s reaction, this news came as a shock to most people and raised many questions, such as is this the time to revisit our exercise recommendations to patients? Should we advise against walking for persons concerned about their bone health or advise them to limit it to shorter time periods?

Clearly, walking is not the same exercise for everyone when taking into account speed, stride length, arm movement, and other unique variables, not to mention differences between the sexes. Is a certain type of walk better than another? Is walking itself insufficient to positively impact one’s bone health? Or is walking perhaps even causing a decline in mineral content if done excessively? Was the increased fracture risk in the Nikander study merely due to increased falls in those who walked for a greater period of time? Weight loss due to the increased caloric expenditure from any exercise may also impact bone health and affect hormonal balance if done to an extreme level. Were the individuals who walked for more than 3 hours a heterogeneous group of persons who walked excessively? Certainly, we need more information before we can use these data in clinical practice. At a minimum, however, I found this presentation to be quite provocative and worthy of further exploration.

I am frequently asked by my patients with osteoporosis whether a certain activity or exercise is “weight-bearing” and good for their bone health. While some believe that they must lift heavy weights to meet the goals of weight-bearing exercise, others wrongly believe that any exercise, including swimming, will suffice. I remember a small woman in her mid-50s, weighing no more than 90 lb, with significant osteoporosis, who eagerly recited every weight-lifting maneuver, from “clean and jerk” to “snatch” and “press”; she had been working out daily in the free weight room at a local gym in hopes of making her bones stronger. She was continually increasing her weight burden and stressing herself to exhaustion at every lift, following advice she was being given by physical trainers at the gym. She had not considered the potential negative consequences of this exercise routine on her frail bones and fell into the trap of thinking “If a little is good, more is better.”

Weight-bearing exercise describes any physical activity done on one’s feet that works bones and muscles against gravity. It is this pull of gravity that sets in motion a positive bone turnover. Bones increase in density when they bear weight during exercise and when there is “impact” or additional strain placed upon them. If the impact is insufficient, the benefit will be negligible and, in fact, one may still lose bone mineral content despite exercising. Excessive impact during exercise, on the other hand, may result in damage to joints, muscles, and even bone by causing microfractures or fractures themselves. This is particularly a problem in the setting of an osteoporotic spine, which is at risk of compression fractures with excess strain.

High-intensity (60%-85% of maximal) progressive resistance training that targets muscles connected to clinically important sites, such as the hip and bone, has been shown to benefit bone mineral density of the spine in men, with no statistical difference noted in women or when only moderate intensity was studied.2 Femoral neck bone mineral density has been shown to statistically increase with a multicomponent exercise program that involves resistance and weight-bearing exercises.3

Exercise also increases muscle strength, which is important for supporting joints and preventing falls and their resultant fractures. Although exercise is recommended as a way to maintain or even build bone mineral density, individuals who already have existing osteoporosis may be more limited in the type of exercises they can do without risking harm. Classic examples of weight-bearing exercises include rapid walking, hiking, and jogging; vigorous yard work and house work; participation in team or racquet sports; dancing, aerobics, and stair climbing; skiing, skating, karate, and bowling; and weight training with either free weights or machines.

While bicycling and swimming are considered to be aerobic exercises and excellent ways to improve cardiovascular health and muscle strength, they are not considered to be classic weight-bearing activities and fail to have as much beneficial effect on bone as other exercises.


Resistance exercise that involves lifting weights is an excellent way to build bone mass, although one should be cautious of excessive burden on already frail bones, as it may result in fractures and injuries to muscles, joints, and tendons. For many, the use of a machine that uses pullies or bands is preferred to free weights in terms of reducing risk of injury. At times, the body itself can serve as the weight in exercises aimed at providing weight-bearing to critical bones.

We are still struggling with exactly how much exercise to recommend to any individual for maximal effect. Most authorities recommend at least 20 to 30 minutes of exercise per day, 4 or more days a week, for maximum benefit to bone, muscle strength, coordination and balance, and cardiovascular health. It is less certain exactly what to recommend to someone seeking benefit for more limited purposes, such as strengthening his or her bones. To maintain optimal benefit to one’s bones, it is thought that the intensity, duration, and amount of stress to the bones must increase over time, and that a combination of resistance training and weight-bearing exercises is ideal.

While studies we read may reflect a unique population characteristic, they clearly raise issues that need further exploration and perhaps incorporation into future recommendations to our patients. Exercise has proven to be beneficial in maintaining bone health, cardiovascular status, flexibility, fall reduction, and psychological improvement. It is also important to advise our patients that to achieve maximal benefit to bone, an exercise program must be accompanied by an adequate intake of calcium and vitamin D and lifestyle modifications, as necessary. Medications and disease states that may predispose adults to a more rapid bone turnover must be dealt with, although genetic predisposition is a risk factor that is not escapable.



1. Nikander R, Gagnon C, Dunstan DW, et al. Frequent walking, but not total physical activity, is associated with increased fracture incidence: a 5-year follow-up of an Australian population-based prospective study (AusDiab). J Bone Miner Res. 2011;26(7):1638-1647.

2. Maddalozzo GF, Snow CM. High intensity resistance training: effects on bone in older men and women. Calcif Tissue Int. 2000;66(6):399-404.

3.  Kukulijan S, Nowson CA, Sanders K, Daly RM. Effects of resistance exercise and fortified milk on skeletal muscle mass, muscle size, and functional performance in middle-aged and older men: an 18-mo randomized controlled trial. J Appl Physiol. 2009;107(6):1864-1873.


Dr. Gambert is professor of medicine and associate chair for clinical program development, co-director, Division of Gerontology and Geriatric Medicine, Department of Medicine, University of Maryland School of Medicine; director, Geriatric Medicine, University of Maryland Medical Center and R Adams Cowley Shock Trauma Center; and professor of medicine, Division of Gerontology and Geriatric Medicine, Johns Hopkins University School of Medicine, Baltimore, MD.