Keeping Bones Healthy Through Exercise

PARIS — Studies looking into the impact of exercise continue to conclude that we all need to get moving, even little kids. So, how strange is it that, at the same time, the levels of inactivity are increasing worldwide?

On January 20, the 36th Scientific Day of the Osteoporosis Research and Information Group (GRIO) took place in Paris. This was an opportunity to remind people that physical activity has a significant influence on building and preserving bone mass.

We all know the public health messages about regular physical activity and its benefits. But what do we, in the year 2023, know about the role that regular physical activity plays in our bone health?

Laurence Vico, PhD, is the director of SAINBIOSE (Health, Engineering, Biology, Saint-Etienne), Unit U1059 of the French National Institute of Health and Medical Research (INSERM). This is the same laboratory that was featured in news stories reporting on the research that she conducted involving cosmonauts on the International Space Station. Vico attended the GRIO event, where she gave an overview on managing osteoporosis without medication.

Sports and Osteogenesis

Some sports are better for bones than others. Physical activities are associated with corresponding ground reaction forces. Examples include weightlifting (three to seven times one's body weight), jumping events (two to eight times one's body weight), running (1.5 to 3 times one's body weight), and walking (one time one's body weight). These mechanical loads stimulate osteoblasts, thus promoting bone remodeling.

By contrast, nonimpact sports — for example, cycling and swimming — are less osteogenic and, as such, significantly less beneficial to bone formation. Nothing new here, except that the latest scientific data are not as clear-cut. What they show is that an increase in bone mass could occur in swimmers, particularly in their upper limbs.

Researchers are particularly interested in sports like tennis and baseball, where one arm or leg is loaded more than the other. This is because the less active limb can act as an internal control for the more active limb. In addition, mean side differences in bone density have been observed in the humerus cortical area among tennis players.

Pediatric Osteoporosis

Being physically active in adolescence increases the chances of having healthier bones later in life. This makes perfect sense in light of biomechanical studies. "They all point in the same direction," said Vico. Intense physical exercise during the peripubertal period provides lasting benefits with respect to bone geometric parameters. According to a computer simulation of the bone remodeling process, the onset of osteoporosis is predicted to be delayed by 13 years if the young adult areal bone mineral density is 10% higher than the mean.

Prepuberty and early stages of puberty are the periods now viewed as the window of opportunity in which to increase peak bone mass. It is, however, known that what matters more than bone mineral density (BMD) is bone size.

Most available studies, though, are still about BMD. For example, there was a meta-analysis of 22 trials conducted in children and adolescents representing all Tanner stages (stage I through stage V). Exercise interventions included games, dance, resistance training, and jumping exercises. All trials in early pubertal children, six in prepubertal children, and two in pubertal children reported positive effects of exercise on bone. Mean increases in bone parameters over 6 months were 0.9%–4.9% in prepubertal children, 1.1%–5.5% in early pubertal children, and 0.3%–1.9% in pubertal children, compared with controls (P < .05).

An earlier study on female tennis and squash players showed that physical activity during the pubescent years is crucial for maximizing bone mass. Whereas there is the potential for exercise-induced bone gain in adults, the benefit is about two times greater if women start their playing careers at or before menarche (humeral side-to-side difference, 17%–24%) than after menarche (8%–14%).

Bones Over Time

More evidence of the benefits of exercise on bone health indicates that engaging in sports over a long period of time helps to keep a higher BMD in later years.

For example, one retrospective study sought to determine the long-term effect of exercise on BMD, bone mineral content (BMC), and body composition in 48 postmenopausal women (54-73 years of age). Half (24) of the women had been elite athletes during their youth; all had long-term (> 20 years) histories of significant training and performance. Half had been swimmers, and half runners. They were age matched with 24 sedentary controls. There were no significant differences in activity levels between athletes and controls at the time of this study.

BMD and BMC were not significantly different between athletes, but they were significantly higher in athletes than in controls. The researchers concluded that physical activity during youth seems to have a beneficial effect on bone mass and helps to prevent bone loss due to aging.

Bone Microarchitecture

It is now clear that trabecular and cortical bone microarchitectures are reinforced by the mechanical stresses induced by physical exercise, but in different ways. "The results of a study published in 2020 support previous findings, showing that these two types of bone — trabecular and cortical — do not behave in the same way," Vico explained.

"What these researchers found was that, no matter what the sport — in this case, cricket, running, swimming, hockey — the trabecular BMD is higher in all athletes, compared with controls. There are no credible differences between different sporting groups. The same cannot be said in terms of the cortical bones," Vico explained. "The study's results suggest that cortical midshaft hypertrophy is associated with impact loading, while trabecular BMD is positively associated with impact and nonimpact loading. This means that depending on the bone compartment, the adaptations are different...For cortical bone, there needs to be discontinuous rather than continuous impacts, having unusual directions and with sufficient force to create a stimulus. As for trabecular bone, we still don't know what type of signal can reach and stimulate bone cells, in particular osteoblasts."

Regarding bone adaptation in athletes who cease or who continue engaging in sports activities, a study of baseball pitchers found that at the level of the humerus, density-weighted polar moment of inertia (which indicates torsional bone strength) and cortical thickness were greater in continuing throwers than in former throwers.

On the other hand, for anything relating to trabecular bone and even BMC, there was no notable difference.

"Due to a different cortical thickness, those who continue the sport benefit in terms of biomechanical properties," said Vico. "It should also be noted that the more developed these properties are, the higher the bone's resistance to fracture. And so, it turns out that BMD, which has always been highlighted, is insufficient for assessing the adaptation of the bone to mechanical stimuli."

Vico, the director of SAINBIOSE, INSERM Unit U1059, reports that she has no relevant financial relationships in connection with this presentation.

This article was translated from the Medscape French edition.

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