Cardio exercise is outstanding for cardiovascular health, respiratory function, insulin sensitivity, mood, and longevity. It is a poor primary tool for changing body composition because it does not address the hormonal and metabolic drivers of fat storage and muscle loss that dominate in adults over 35. Using cardio as the primary body composition intervention is one of the most common fitness mistakes made in this age group.
The Energy Compensation Problem
The body compensates for caloric expenditure from exercise through multiple mechanisms: increasing hunger, reducing non-exercise physical activity, and reducing resting metabolic rate. Research by Herman Pontzer at Duke University has shown that total daily energy expenditure reaches a plateau regardless of exercise volume in sedentary individuals beginning exercise programmes. This compensation effect is strong enough that additional cardio volume often produces little additional caloric deficit beyond a moderate starting point.
Why Resistance Training Beats Cardio for Body Composition
- Muscle tissue is metabolically active: each kilogram of muscle burns approximately 13 calories per day at rest, so adding muscle increases resting metabolic rate permanently
- Resistance training produces elevated post-exercise oxygen consumption for 24 to 48 hours after training
- Unlike cardio, resistance training does not produce meaningful muscle loss during caloric restriction when protein intake is adequate
- Resistance training improves insulin sensitivity specifically in muscle tissue, the largest glucose sink in the body
The Optimal Combination
Resistance training two to three times per week as the primary body composition intervention, combined with moderate steady-state or interval cardio for cardiovascular health, is the evidence-based approach for adults over 35. The cardio does not need to be extensive: 150 minutes of moderate intensity per week meets all cardiovascular health targets without compromising resistance training recovery.