Exploring the Relationship Between Physical Activity, Energy Expenditure, and Body Composition
- Julian Simpson
- Mar 30
- 3 min read
Exploring the Relationship Between Physical Activity, Energy Expenditure, and Body Composition
As individuals progress through the various stages of life, particularly into their later years, a notable trend emerges: body fat levels typically increase. This phenomenon can be attributed to several interconnected factors, the most significant being a decrease in physical activity levels and a diminished resting metabolic rate. As people age, they often engage in less vigorous exercise and physical movement, leading to a gradual accumulation of body fat. Concurrently, there is a decline in fat-free body mass, which encompasses not only muscle mass but also vital components such as organs and tissues that do not store fat. This decline in fat-free mass is a critical aspect of the aging process and can have profound implications for overall health and well-being.
Fat-free mass is essential for maintaining a healthy metabolism, as it includes both muscle tissue and high metabolic rate organs such as the brain, liver, and kidneys. These components collectively require a higher energy expenditure compared to fat mass, which is relatively inert in terms of metabolic activity. The loss of fat-free mass not only contributes to a decreased metabolic rate but also impacts various physiological processes, including hormone regulation and nutrient utilization. Therefore, the balance between fat mass and fat-free mass is critical for maintaining optimal health as one age.
Extensive research has demonstrated that a 1–2% decline in fat-free mass associated with the aging process is closely linked to a corresponding decrease of approximately 1–2% in resting metabolic rate for each decade of life in adults. This gradual decline can lead to a cycle of weight gain and further loss of muscle mass, exacerbating the challenges associated with aging. As muscle mass diminishes, individuals may find it increasingly difficult to engage in physical activities, leading to a sedentary lifestyle that further accelerates the decline in both muscle and metabolic health.
Moreover, increased muscle mass is often correlated with higher levels of physical activity, which itself can significantly stimulate appetite. Engaging in regular physical exercise not only helps to preserve and build muscle mass but also encourages a healthier appetite and nutritional intake. This relationship highlights the importance of maintaining an active lifestyle, as it can create a positive feedback loop that supports both muscle health and overall well-being.
It has been observed that inadequate food intake, often associated with conditions such as anorexia, can lead to a significant decrease in exercise capacity, muscle mass, and strength. These factors are major risk contributors to the development of frailty and sarcopenia in older adults. Sarcopenia, characterized by the progressive loss of muscle mass and strength, poses serious health risks and can significantly impair quality of life, making it imperative to address nutritional needs alongside physical activity.
There is clear and compelling evidence that regular and appropriate physical activity in older age plays a crucial role in enhancing muscle strength, increasing physical functioning, and maintaining an independent lifestyle. Health experts recommend that older adults (≥ 65 years) engage in at least 150–300 minutes of moderate physical activity or at least 75–150 minutes of vigorous physical activity, or a combination of both, each week. This level of activity is vital for preserving muscle mass, enhancing cardiovascular health, and improving overall physical fitness.
Furthermore, it is recommended that older adults participate in combined bone and muscle strengthening activities—such as carrying heavy bags, engaging in gym workouts, or practising yoga—at least twice a week. These activities are essential for keeping muscles, bones, and joints strong and functional. Additionally, older adults should also engage in balance activities such as dancing, playing bowls, or practising Tai Chi at least twice a week. These exercises are particularly important for reducing the risk of frailty and falls, which are common concerns in the aging population. By incorporating a comprehensive approach to physical activity that includes strength training and balance exercises, older adults can significantly improve their health outcomes and enhance their quality of life.
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Dericioglu, D., Methven, L. & Clegg, M.E. Does physical activity level and total energy expenditure relate to food intake, appetite, and body composition in healthy older adults? A cross-sectional study. Eur J Nutr 64, 71 (2025). https://doi.org/10.1007/s00394-024-03571-z
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