Age-related declines in marathon performance result from interacting physiological, neuromuscular and behavioral changes that accumulate over decades. Evidence-based reviews identify a few dominant mechanisms that explain most of the drop in sustained speed and endurance.
Central and peripheral oxygen transport
The largest single factor is loss of maximal aerobic capacity. VO2max declines with age because maximal heart rate, stroke volume and peripheral oxygen extraction fall. Hirofumi Tanaka at the University of Texas at Austin and Dale R. Seals at the University of Colorado show that reductions in maximal cardiac output and mitochondrial oxidative capacity explain much of the endurance loss, and that lifelong training attenuates but does not eliminate this decline. This means older marathoners can preserve performance by maintaining high training but will still face physiological headwinds compared with younger runners.
Muscle, strength and biomechanics
Muscle mass and neuromuscular function also shift with age. Sarcopenia—the progressive loss of muscle size and type II fibers—reduces propulsion and increases fatigue during long runs. Changes in tendon stiffness and neuromuscular coordination negatively affect running economy, so older athletes often expend more energy for the same speed. Guillaume Lepers at Université de Bourgogne has documented age-related slowing in marathon and long-distance events and links part of the decline to decreased muscle power and altered biomechanics. Strength training and technique work can partially counter these losses but cannot fully restore youth-level power.
Hormones, recovery and health risks
Endocrine changes such as lower testosterone and growth hormone, impaired immune and repair responses, and slower recovery rates increase injury risk and reduce tolerable weekly training volume. The American College of Sports Medicine provides guidance showing that modifying intensity, increasing recovery, and including resistance and cross-training reduce performance losses. In hotter climates or at high altitude, thermoregulatory decline and decreased heat tolerance further magnify performance gaps for older runners.
Together these factors create predictable consequences: slower race times, greater variance in decline depending on lifelong training, and increased importance of targeted interventions (strength work, higher-quality recovery, heat acclimation). Cultural and territorial nuances matter: communities with strong masters programs, accessible medical support, and social incentives for continued training often show smaller declines because older athletes maintain volume and motivation. Ultimately, evidence from Tanaka, Seals, Lepers and institutional guidance from the American College of Sports Medicine indicates that the most influential age-related drivers are declines in VO2max, muscle mass/strength, and altered recovery and hormonal capacity, all of which interact with environment and training to determine marathon performance.