Many factors must gel together to result in running quicker: training consistency, volume, intensity, frequency and recovery are all equally as important as bodyweight. If you want to run quicker it’s definitely worth looking at all these factors. With the first five, it’s generally a case of a little more is a little better, as long as it fits with your lifestyle. With bodyweight though, it’s worth considering your aims and goals within the sport.
If we consider elites across all sports, pretty much all of them fall into body-type categories depending on what they compete in. This is no coincidence, because performing at the highest level will undoubtedly lead to a body shape that the training dictates. For swimmers, this means broader shoulders and reasonable body fat to aid buoyancy; for cyclists you’ll often see bigger quads due to increased leg work; and for runners a more slender frame to allow them to carry as little non-functional weight as possible. In triathletes, you’ll see a combination of all three.
For age-groupers, it’s worth considering your options from the direction of health before performance. If you feel you’re carrying a bit of excess weight in the form of body fat, then appropriate training combined with a sensible diet should see this change. But beware, as too much weight loss isn’t healthy and can lead to a number of complications, both with your day-to-day health and your performance. Your body needs fat to function properly, and is particularly beneficial to the immune system and for regulating your body temperature.
Another thing to consider is what type of weight you’re losing: if it’s in the form of muscle you may well be reducing your ability to stay strong in races and training. If you’re worried about this, book in for a body composition analysis.
In short, lighter may often mean quicker when running. But if it’s at the expense of strength, a healthy body, lifestyle and mind you need to decide whether it’s worthwhile for you and your current situation.