This is an excellent review of the literature where the authors evaluated the natural decline in muscle mass associated with aging. The authors reviewed 47 studies in which CTs, MRIs, and/or ultrasound devices were used to measure muscle volume in an accumulated total of 982 younger adults (average age 25) and 1003 older adults (average age 75). What made this paper interesting is that the authors compared nine different muscle groups to determine if some muscles atrophy at quicker rates than others. To their surprise, the authors determined that some muscles atrophy at nearly 5 times the rate of others. The rectus femoris muscle was the most sensitive to atrophy, losing approximately 33% of its mass over the 50 year period. As a whole, the quadriceps lost 27% of its volume and the elbow flexors and extensors lost 20% of their mass. The hamstrings lost 19% and the adductors lost 13% of their mass. Interestingly, the low back extensors lost 24% of their mass while the psoas muscle decreased in volume by 29%. The authors cite several references showing that while the paraspinal muscles do not appreciably atrophy until the seventh decade of life, the psoas muscle has been shown to atrophy while people are in their 40s and 50s. The authors state that interventions to prevent age-related muscle mass decline should be muscle-specific and “may need to be initiated earlier in the psoas.” This statement is important as weakness of the psoas often results in impaired ground clearance while walking, resulting in a heightened risk of falling.
The authors also evaluated differences between men and women, noting that women were more likely to atrophy in their adductors, ankle dorsiflexors and calf muscles than men. In both groups, soleus was the least likely to atrophy, which the authors attributed to its high density of slow twitch muscle fibers (soleus is almost 100% slow twitch muscle fibers). Several studies show that sarcopenia targets fast twitch muscle fibers, which are more difficult to maintain as they need higher force output in order to preserve volume. The authors point out that to date, there have been no studies of important muscles of the foot and leg, such as flexor digitorum brevis, flexor hallucis longus, tibialis posterior, peroneus longus and/or brevis, which is unfortunate because atrophy in these important muscles has been correlated with impaired walking ability, reduced walking speed, along with a heightened risk of falling.
The main take away from this study is that it is important to maintain strength starting in your 40s and 50s, and these exercises do not need to be intense. Some great research has shown that performing three sets of 10 repetitions at a moderate intensity just once a week is enough to maintain muscle mass (1). This is important because compliance with intense exercise programs in people over the age of 60 is extremely low. The following article (https://www.humanlocomotion.com/five-simple-exercises-to-prevent-age-related-muscle-loss/) reviews five simple exercises that can be done just once a week to prevent age-related decline in muscle mass. A video of this routine is available on YouTube at the following link ( https://youtu.be/dBbPsJKq9uM).
- Létocart A, et al. Muscles adaptation to aging and training: architectural changes–a randomised trial. BMC geriatrics. 202;21:1-8.