Muscle Strength Positively Predicts Bone Outcomes in Aging Men

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MUNICH – As men get older their muscle strength drops, and this can serve as a significant predictor of bone outcomes, shows a UK study conducted in men over age 40 years.

The findings highlight the importance of looking not only at muscle mass but at the various components of muscle strength as men age and their risk of fracture and fall increases, said Ayse Zengin, PhD, Medical Research Council, Human Nutrition Research, Cambridge, United Kingdom, who presented the results of her study during a poster tour here at the European Congress of Endocrinology (ECE) 2016.

"We found negative associations with...age and muscle force, age and muscle power, and age and cross-sectional muscle area," she said. "We also saw positive associations between muscle force and all cortical bone outcomes at the tibia."

Of particular interest, the findings showed a significant interaction between ethnicity and muscle power. "White and south Asian men showed a greater negative association between age and muscle power than black Afro-Caribbean men," Dr Zengin pointed out.

These findings may contribute to the understanding of fracture incidence in different ethnic groups, she added.

Muscle Force and Power, Not Muscle Mass Alone

Explaining what motivated the research, Dr Zengin said that much prior work has investigated changes in bone and muscle strength in women because of the recognized health changes associated with menopause, including an increased risk of obesity, osteoporosis, and associated fracture. But "there are relatively few studies of bone health in older men, especially in the UK and in relation to ethnicity," she told Medscape Medical News in an interview.

And she emphasized that the consequences of a fracture in men are worse than in women. "Even though they have fewer fractures than women, they have increased mortality following a fracture."

The researchers specifically looked at muscle force and power rather than muscle mass alone, as the latter has long been used as a surrogate for muscle strength, but this does not hold true for the aging population.

"Studies have shown that there's a far more rapid decline in muscle strength than muscle mass and that younger and older men can have the same muscle mass, but older men cannot perform functional tests as well as younger men," Dr Zengin said. She noted the importance of measuring direct components of muscle strength, that is, mass in addition to anatomy, muscle fiber types, fiber distribution, and force-generating capacity and power.

 

Previous studies have shown that an increased risk of falls is associated with decline in muscle power, a factor that reflects how fast someone can produce force, for example, when correcting or maintaining balance prior to a fall, she explained.

She noted that some data exist on general bone changes in men, but there are few data on functional measures of the muscle and bone relationship during aging. For this reason, she and her colleagues investigated the association between lower-limb muscle strength and age, as well as tibial-bone outcomes and muscle force.

In total, 301 men over 40 years of age were recruited, including European white (n = 201), Afro-Caribbean black (n = 43), and south Asian (n = 57). To assess indicators of bone strength and status, peripheral quantitative computed tomography was performed at the tibia.

 

Outcome measures were cortical bone-mineral content (BMC), cross-sectional area of bone, cortical area of bone, and cross-sectional moment of inertia, which is an indication of bone-bending strength. Participants also performed jumping mechanography, which involves a single two-legged jump on a ground reaction-force platform, which directly measures muscle force (kN) and power (kW) in the lower limbs.

These outcomes were expressed as percentage of unit change in age, adjusted for ethnicity, weight, and height, and were –0.4%, –1.8%, and –0.4% for muscle force, muscle power, and cross-sectional muscle area, respectively (all P < .0001).

"With muscle power we saw significant ethnicity interactions where white and south Asian men had greater negative associations with muscle power and age as opposed to Afro-Caribbean men," Dr Zengin noted. She emphasized that this was significant because muscle power is strongly associated with fall risk, and Afro-Caribbean men have a lower fracture incidence compared with white and south Asian men.

 

But no differences were found between ethnicities in tibial-bone changes, so all the men were grouped together in that analysis. For every 1-kN increase in muscle force, there was a 8.5% difference in cortical BMC, a 9.3% increase in cross-sectional area, and a 9.3% increase in cortical area (all P ≤ .001).

In particular, she highlighted the change in the cross-sectional moment of inertia. "We saw that force predicted the greatest difference in cross-sectional moment of inertia. For a 1-kN increase in muscle force, we saw a 18.6% difference in this outcome."

Future Studies Need to Examine Ways to Maintain Muscle Strength

Dr Zengin said further research is required to better elucidate relationships between muscle strength and bone outcomes, and then interventional studies are needed to provide a strategy to prevent fractures.

 

"Men need to maintain muscle power and prevent associated falls. Endurance training would help to load the bone and maintain the muscle power and bone strength that is there," she observed.

Francesca Marta Elli, PhD, from the University of Milan, Italy, who comoderated the poster tour, asked if the differences in ethnicity were most likely because of differences in genetics or lifestyle. Dr Zengin said that genetics was likely to play a big role but added that lifestyle factors probably also play a part. "For example, men from South Asia eat a different diet and have different activity habits, and this, of course, affects the associations we see."

Also moderating was Geert Carmeliet, MD, from KU Leuven University, Belgium, who observed that, if it is the case that muscle power influences the bone, it would be interesting to find out if this is a local or systemic effect, and if local, if it would be possible to measure an effect on the spine.

 

Dr Zengin pointed out that it is difficult to measure the effect of muscle force or power on the spine, but they had performed the same investigation on the upper limbs using grip strength to measure muscle force. "We saw consistent associations between cortical bone outcomes at the radius and grip strength, similar to our findings at the tibia."

Drs Zengin, Elli, and Carmeliet have reported no relevant financial relationships.

European Congress of Endocrinology 2016. May 29, 2016.