strength across a lifespan
Building, Maintaining, and Adapting Muscle Health
from Youth to Adulthood
By Elyse Lovett, MBS, MS
Strength plays an important role at every stage, but at each stage strength is defined differently based on age and physical development. Whether it is building a foundation in youth, maintaining muscle mass in adulthood, or preserving function and independence in older years, strength is a central component of health and well-being.
Twenty years ago, strength represented how much you can “lift” focusing on power and maximum performance such as bench presses, squats, or deadlifts. In recent years, the understanding of strength has changed to include functional fitness, endurance, and overall health. Strength now encompasses the importance of joint stability, recovery, cognition, and mobility and reflects a more of comprehensive approach.
A key component of strength has changed to functional fitness instead of maximum amount of weight one can lift. There is a greater emphasis now on how well the body can perform overall and how it adapts to physical challenges. This includes improving stability and coordination to perform better and reducing the risk of injury.
Strength as a Foundation
The development of strength begins during the early years and plays a role in bone health, metabolic function, and body composition. During infancy and early childhood, strength is primarily influenced by neurological factors vs. muscle hypertrophy as it is later in life. The rapid development of the nervous system enables the coordination of muscle activity so early life activities like crawling, standing, and walking can be accomplished. In later childhood years, muscle hypertrophy is attributed to testosterone and growth which continues through early adult life.
Strength training helps athletes improve performance, support motor skill acquisition, and reduce the risk of injuries. At the core of strength training in adolescent years is resistance training which may increase muscle strength, power, and endurance. Studies have shown that resistance training enhances athletic development and promotes long-term health benefits that extend into adulthood.[1]
Resistance training offers benefits such as improved health fitness, injury rehabilitation, and injury prevention. With proper supervision and emphasis on technique, young individuals can safely build strength with minimal risk. Gains in childhood strength are primarily attributed to the neurologic mechanism of increases in motor recruitment, allowing for increases in strength without resultant muscle hypertrophy. When children engage in resistance training, their nervous systems become more efficient at activating and coordinating motor units. Essentially the brain and the nervous system learn to “communicate” better with muscles, enhancing coordination and control. This process enables children to experience notable strength improvements while maintaining a leaner physique.[2]
In adolescents, resistance training offers a range of benefits that can extend beyond muscle building including improving insulin sensitivity, regulating blood sugar levels, increasing lean muscle mass, and reducing body fat. A 2023 meta-analysis of 35 studies, comprising of children and adolescents with overweight and obesity showed that exercise training is effective for lowering fasting glucose, fasting insulin, and body weight.[3]
Peak Strength and Maintenance
Between the ages of 20 and 30 individuals reach their peak muscle mass and strength. This period is crucial for establishing long-term habits that helps maintain strength and physical health into later life. During this period, muscle mass and strength are highest due to hormonal influences, particularly levels of testosterone and growth hormones. Studies have evaluated how age impacts muscle mass and strength in young adults. One study that included 12 weeks of progressive resistance training of 826 participants aged 18-39 years showed that age was positively correlated with muscle size and strength in untrained young adults. In addition, the effect of age was small relative to the improvements induced through resistance training, thus suggesting age does not limit response in any practical way during early adulthood.[4]
Hormones and strength
Hormones play a crucial role in regulating muscle strength, growth, and recovery.
Testosterone plays an important role in the strength development during peak strength and maintenance years acting as a key hormone in muscle growth, recovery, and physical performance. Testosterone peaks during puberty and early adulthood, contributing to gains in muscle size and strength in adolescents. Testosterone enhances protein synthesis and inhibits protein degradation, which are essential for muscle growth and repair following resistance training. Individuals with higher testosterone levels experience more significant strength gains and faster recovery after exercise. Additionally, testosterone influences neuromuscular adaptations which increases power output and overall strength. Age and sex influence testosterone responses, with boys experiencing increases post-puberty and men seeing a gradual decline in testosterone after age 35. To induce an acute testosterone response, resistance exercise should have high volume and metabolic demand.[5]
Growth hormone is another key hormone that influences strength and muscle development. The hormone is produced through the pituitary gland and secreted into the bloodstream for metabolic functions such as cell growth, regeneration, and repair. Growth hormone is especially important for muscle hypertrophy, recovery, and metabolism. Similar to testosterone, growth hormone peaks during adolescence and early adulthood and then gradually decreases with age. Research has shown that growth hormone is crucial for linear growth and bone and muscle development. Growth hormone deficiency can lead to decreased bone and muscle mass and strength, potentially increasing fracture risk. [6]
One of the primary roles of estrogen in younger adults is its impact on muscle recovery and regeneration. Estrogen helps reduce muscle damage after intense physical activity by acting as an antioxidant and reducing inflammation. Estrogen, like testosterone, plays a role in muscle protein synthesis. Studies have shown it has a mild anabolic effect, promoting the maintenance of lean muscle mass. In addition, estrogen helps maintain bone density by promoting the activity of osteoblasts which are the cells responsible for bone formation. In younger adults, this means stronger bones essential for supporting muscles strength and reducing the risk of fractures and injuries during resistance raining.
Estrogen tends to fluctuate throughout a women’s menstrual cycle, and these fluctuations can influence strength and performance. During the follicular phase, estrogen levels rise, reaching their peak just before ovulation. The increase in estrogen has been linked to enhanced muscle strength, endurance, and recovery. Many women report feeling stronger and more energetic during the latter part of the follicular phase. More research is need much of the research that is currently published is divided on the whether menstrual cycle hormonal changes do or do not affect a women’s metabolism during exercise.[7]
“Strength has always been measured through how much someone can lift, but strength is so much more comprehensive than just how much you can bench press in the gym. Physical strength in sports is important, but emotional and mental strength at times can overpower physical strength. Within the past decade, there has been a significant rise in the recognition of mental strength. Additionally, society has shifted to a greater acceptance of appreciating women’s strength, not just in the context of physical capability but also in leadership. The conversation around vulnerability as being an aspect of strength has also come to life. Collectively the voice around strength being “masculine” has shifted to much more.”
Katie Emerson, MS, RD/LDN, CISSN
MAINTAINING STRENGTH IN LATER YEARS
As we age, muscle mass and strength naturally decline. The loss of muscle can impact mobility and independence, increasing the risk of falls and fractures. Once of the most significant conditions directly related to aging and strength is sarcopenia which is a gradual loss of muscle mass. This condition leads to reduced physical function, increased fall risk, and possibly a poorer quality of life for older adults. Age-related sarcopenia becomes relevant at around age 60 and beyond. Several factors contribute to the onset and progression of sarcopenia including age-related hormonal changes where hormonal changes, such as reduced levels of growth hormone, IGF-1, testosterone, and estradiol play a significant role in sarcopenia. [8]
A sedentary lifestyle exacerbates muscle loss. Muscles that aren’t used regularly experience a decline in strength and mass. A meta-analysis of 25 studies showed a statistically significant association between physical activity and a reduced risk of sarcopenia with physical activity lowering the chances of developing sarcopenia. Various types of physical activity, including resistance training and aerobic activities were found to have protective effects on muscle mass and strength, confirming physical activity’s role in healthy aging.[9]
“The major need or push is to engage in lifelong exercise as a means of preventing or reducing muscle mass loss as we age. Sarcopenia is the term quite commonly used for age associated muscle loss. Sarcopenia is associated with the risk of or actual development of other medical conditions due to increased frailty over time. Being engaged in exercise, resistance exercise helps offset this, hence over the past decade there has been a push to get more adults engaged in exercise.“
Doug Kalman PhD, RD, FACN, FISSN
Building strength throughout life involves specific dietary and supplement recommendations that target different age groups. In early childhood, recommendations include protein, healthy fats, and complex whole-foods based carbohydrate sources that provide sustained energy, fiber, and nutrients. In adolescence and young adulthood, strength focus should be on muscle growth and mass, hormonal changes, optimizing metabolism, lean bone mass development, and maintaining strength. Dietary recommendations include high-protein foods, whole grains and fiber-rich carbohydrates, iron-rich foods, as well as healthy fats. Protein supplementation may be beneficial to support muscle building and recovery. Additionally, it is important to address low intakes of calcium, vitamin D, and omega-3 fatty acids in this group. For those engaging in sports or resistance training, creatine-based supplements can be useful, while branched-chain amino acids may aid in muscle recovery.
Adulthood focuses on continued muscle growth but also maintaining muscle mass and supporting joint health. Food recommendations are similar to those for young adults but with the addition of ani-inflammatory foods such as fatty fish, nuts and seeds. In addition, supplementation can include all those through younger years plus the addition of supplements for joint support including glucosamine, chondroitin, MSM, and collagen.
Summary
Throughout all stages of life, strength training plus proper nutrition and supplementation is key to optimizing muscle and joint health. A targeted plan throughout the stages from early childhood neurological adaptations to combating sarcopenia in older year can help ensure long-term strength. By focusing on high-quality proteins, complex carbohydrates for energy needs, anti-inflammatory nutrients, and age-appropriate supplements, individuals can maintain strength, reduce the risk of injury and support healthy aging through their lifespan.
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