New York, Oct 29 (IANS): Love to notch up the race numbers on the treadmill each day? Be careful, as running with heavier shoes may slow your race times, researchers have found.

The study found that running times slows when shoe weight is increased, even if only by a few ounces.

For the study, the researchers from the University of Colorado-Boulder in the US brought 18 runners, measured energy consumption and 3,000-metre race times in runners wearing shoes of various weights.

To measure running economy, each participant ran on a treadmill using three pairs of nearly identical shoes, with subtle differences.

Unknown to the runners, the researchers added small lead pellets inside the tongues of two of the three pairs of shoes to be used by each runner.

While one pair was normal, each shoe of another pair was made 100 grams heavier and a third pair was loaded with 300 grams of lead pellets per shoe.

Each of the runners ran treadmill tests in which oxygen consumption and carbon dioxide production were measured with all three differently weighted shoe pairs.

The results showed that energy costs of the runners rose by about 1 per cent with each extra 100 grams of shoe weight.

On the other hand, when shoe mass is reduced, by compromising with cushioning for example, it doesn't mean you will run faster, said lead author Wouter Hoogkamer, postdoctoral student at University of Colorado-Boulder, adding "Lighter is not always better."

Prior studies have also shown that proper cushioning also reduces the energetic cost of running.

So when selecting footwear, be aware of this trade-off between shoe mass and cushioning, concluded the researchers in the paper published online in the journal Medicine & Science in Sports & Exercise.