The Effects of Concurrent Training Versus Aerobic or Resistance Training Alone on Body Composition in Middle-Aged and Older Adults: A Systematic Review and Meta-Analysis.
Overview
Muscle mass decline starts at around 30 years old, accelerating after 50. Given the demographic changes and the growing population of middle-aged and older adults, it is crucial to develop strategies for managing sarcopenia (age-related muscle loss) effectively. Exercise and physical activity are effective interventions for older adults, enhancing cognitive function, cardiometabolic health, fitness, muscle mass, and strength. While resistance training (RT) targets fat reduction and muscle maintenance, aerobic training (AT) is more widely studied. Combining AT and RT is known as concurrent training (CT) and may maximize benefits given age-related changes in muscle and fat distribution.
Introduction
Athletic events can be either ‘endurance‐based’ or ‘strength–power‐based.’ An increase in endurance capacity can be achieved through endurance-based training characterized by sustained (>60 min) or repeated intermittent bouts of submaximal contractions when practiced over months or years eliciting metabolic and morphological adaptations in the muscle tissue. In contrast, strength/power training requires short duration (<60 s) high-intensity maximal efforts, and heavy resistance exercises to stimulate myofibrillar protein synthesis and muscle hypertrophy (Damas et al. 2015). The concurrent development of muscular endurance and strength/power remains debatable. Development of hypertrophy may be impaired when endurance training is involved through inhibition of the muscle protein synthesis and Akt/mTOR signaling pathway stream. (Coffey et al, 2017)
One meta-analysis suggests that concurrent training (CT) negatively affects lower-body strength in trained individuals. Another meta-analysis indicates that CT does not hinder muscle hypertrophy, although the extent of improvement may be attenuated.
The purpose of this meta-analysis study is to conduct a comprehensive meta-analysis focused on middle-aged (50–64 years) and older adults (≥65 years) to explore CT’s effects on body composition.
Therefore, the study hypothesis is whether:
- CT would be as effective as AT or RT alone for fat reduction and muscle mass increase.
- CT would outperform AT in decreasing adiposity and enhancing muscle mass.
Study Parameters
A comprehensive search across multiple databases dated to March 2024 was conducted targeting randomized trials comparing concurrent training (CT) with aerobic training (AT) and/or resistance training (RT). 4456 records were found online, with only 53 articles included in this systematic review that met the current research inclusion and exclusion criteria.
Inclusion Criteria:
- Studies that included middle-aged subjects (50 to <65 years) and older adults (≥65 years) regardless of health status and biological sex (with or without chronic diseases)
- Studies that involved CT, including a combination of AT and RT, whether performed in the same or separate sessions
- Balance and flexibility exercises were included if part of the CT program
- No limitations on the intensity, duration, or frequency of exercise sessions
Exclusion Criteria:
- Studies involving trained/athletic older adults
- CT protocols that use high-intensity interval training (HIIT) instead of AT
The following end points or body compositions were evaluated for each intervention:
- Primary Outcomes: body fat percentage (fat %), waist circumference, lean body mass (LBM), muscle mass, and muscle/fiber cross-sectional area (CSA)
- Secondary outcomes: Body weight and body mass index (BMI)
Results:
- First Hypothesis: CT would be as effective as AT or RT alone for fat reduction and muscle mass increase.
CT versus AT
- CT is significantly more effective than AT alone for increasing body weight and lean body mass.
- BMI, body fat%, fat mass, visceral fat mass, muscle mass/volume and waist circumference did not show significant differences between CT and AT alone.
CT versus RT
- There were no significant differences between CT and RT alone for changes in body weight, BMI, body fat %, fat mass, lean body mass, and waist circumference.
- This emphasizes the benefits of CT without impacting the advantages of RT.
Thus, this supports the hypothesis that CT can be considered an effective strategy for maintaining and increasing body weight, specifically muscle mass, and for improving body composition in this age group.
- Second Hypothesis: CT would outperform AT in decreasing adiposity and enhancing muscle mass
The role of AT on the reduction of adiposity and visceral fat has been ranked best for improving body weight and BMI. Key Findings in this ‘head-to-head’ comparison:
- When comparing CT with AT alone, significant differences were observed. This suggests that CT (a combination of AT and RT) may have distinct benefits over AT alone.
- However, when comparing CT with RT alone, no greater adiposity (fat) loss was found. This implies that RT alone might be just as effective as CT in reducing fat.
These findings highlight that CT offers unique advantages over AT and doesn’t necessarily outperform RT in terms of fat loss.
This could guide individuals or professionals in tailoring exercise programs based on specific goals, such as fat reduction or overall fitness
Limitations:
- Significant heterogeneity was observed across various outcomes, likely influenced by differences in study methodologies, participant health statuses, ages, and biological sexes.
- Measuring primary outcomes with less reliable techniques, such as bioelectrical impedance analysis (BIA) and skinfold methods, may have impacted the validity and significance of the findings.
- Unequal volumes of concurrent training (CT) and resistance training (RT) in studies present a limitation, and the results should be interpreted cautiously.
- Furthermore, the exclusion of trained or athletic older adults aimed at enhancing the generalizability of findings may have restricted the ability to derive conclusions about the effects of combined training in athletic older individuals.
Conclusion And Real-World Application
Sarcopenia in older adults increases the risk of cardiovascular and metabolic diseases especially because aging is associated with increased adiposity, making long-term weight loss difficult. Key takeaways:
Concurrent Training (CT) vs. Aerobic Training (AT) and RT:
- CT is as effective as RT and superior to AT for increasing muscle mass in older adults, without compromising muscle hypertrophy.
- CT does not cause the “interference effect” (a potential reduction in strength and muscle growth) often associated with combining AT and RT in middle-aged and older adults.
Practical Applications of CT:
- CT is beneficial for sarcopenia management and can be integrated into rehabilitation, senior fitness programs, and community initiatives to improve quality of life, reduce cardiovascular risks, and manage weight.
- The effectiveness of CT depends on factors like age, training status, biological sex, exercise type, and timing. Fatigue from larger volumes of CT may affect muscle mass outcomes. Negative effects of CT have been observed in men who regularly exercise.
Importance of dietary protein intake:
- Protein is vital for older adults to maintain an anabolic state and reduce sarcopenia.
- High protein intake isn’t strongly linked to impaired kidney function in healthy individuals but should be approached carefully in older adults due to possible declining renal function.
- Caloric/protein restriction could protect against sarcopenia via pathways like mTORC1 inhibition and autophagy, though these effects are complex and influenced by age and other factors.
Further Research Needed
CT could promote long-term benefits in the elderly, as it integrates both aerobic and resistance training elements, promoting overall health and functional capacity. There are several moderators impacting the muscle hypertrophy growth including age, BMI, sex and intervention duration and becomes more significant in middle-aged than older adults (≥65 years).
To address these gaps, future research should prioritize investigating the effects of exercise intensity and volume on muscle mass whilst taking the factors that influence the changes in both trained and untrained older adults and expanding the scope to encompass athletic populations.