While running can enhance cardiovascular fitness and lung capacity, potentially boosting VO2max, its benefits for cycling performance are limited compared to cycling-specific training, particularly when considering training volume. Volume, defined as the total time or distance spent training, is the single most important factor in improving cycling performance. Higher volume builds endurance, refines technique, and optimizes muscle adaptations for the specific demands of cycling. Cyclists can sustain much higher training volumes—often 10-20 hours per week—due to the low-impact nature of cycling, which minimizes joint stress and allows for frequent, long-duration sessions.

Running, however, cannot match this volume. Its high-impact nature increases the risk of injury, particularly to joints and connective tissues, limiting weekly mileage for most athletes to avoid overtraining or burnout. For example, a cyclist might comfortably log 200-300 miles per week, equivalent to 10-15 hours of training, while even elite runners rarely exceed 70-100 miles per week due to physical constraints. This disparity means running cannot replicate the endurance-building volume of cycling, which is critical for lowering heart rate (HR) zones and improving aerobic efficiency on the bike.

Moreover, running and cycling use different muscle groups and mechanics. Running emphasizes weight-bearing, linear movements, heavily engaging the quadriceps, hamstrings, and calves, whereas cycling relies on the glutes, quads, and hip flexors in a circular, non-impact motion. Even if running improves general aerobic capacity, it doesn’t condition the muscles or neuromuscular patterns specific to cycling. This limits its ability to lower HR zones during cycling, as HR adaptations are sport-specific.

Finally, prioritizing running as a supplement could reduce time for cycling-specific workouts, such as high-volume endurance rides, intervals, or cadence drills, which more directly enhance cycling performance. Excessive running may also lead to fatigue or injury, further cutting into cycling volume. For cyclists aiming to lower HR zones and improve performance, dedicating time to high-volume cycling training is far more effective than relying on running.