When running, surplus weight (fat mass to be more precise) can have several negative repercussions on the body: increase in heart rate and hence oxygen consumption, increase in body temperature during exercise, increase in energy expenditure as well as an increase in the pressure exerted on the bones and joints.
Weight is a key factor in defining the oxygen consumption of sportsmen and women, particularly when it comes to identifying the threshold at which the maximum volume of oxygen consumed is attained (VO²max). For a runner, this maximum value is associated with a specific speed:the Maximum Aerobic Speed. Developing the MAS in training therefore leads to an increase of the running speed at which your volume of oxygen is maximised.Reducing fat mass reduces your need for oxygen and reduces the energy expenditure associated with your running stride, which therefore leads to an improvement in this speed.
Indeed, an American survey by the National Runners Health Study on 4700 users showed that a 2 kg change in weight can lead to a difference of almost 1 minute on a 10 km run!
LOSING WEIGHT… BUT NOT TOO MUCH
Finding a balance, in other words, your fitness weight, therefore contributes to optimising your running capacity and preserves your body's energy levels when exercising. The fitness weight should not be too close to the minimum recommended level for your fat mass ratio. This is the case for the "racing weight" reserved for high-level athletes whose medical condition is monitored regularly.
However, take care not to become underweight!Excessively reducing fat reserves can have a negative effect at the end of a long race because the body taps into this energy reserve when your glycogen reserves have been exhausted? It is therefore advisable not to fall below 10% of fat mass as a proportion of total weight for men and 15% for women.
For all amateur runners, the genuine fitness weight must depend on a general feeling of well-being on a daily basis and during your exercise sessions!