How to reach your optimal bodyweight for triathlon

Apart from training smarter and harder, the next best way to get faster is to hit your optimal body weight. Joe Friel shows you how…


What can you do in the off-season to improve your running and hill climbing on the bike? Besides training harder and smarter, the next most effective way for some athletes is to lose a little weight.


There’s little doubt that being lighter means better climbing and faster running. A kilogramme of excess body weight requires 3-4watts of power to get it up a hill on a bike and costs about 4secs per mile when running.

That doesn’t sound like much, but say you drop 3kg. That means you would ride up a hill about 5% faster. On a very hilly Ironman bike course that could save you at least 4mins, and you could take another 5mins off the marathon. That’s a significant improvement in performance.

While there’s no question that excess body weight is a great handicap in triathlon, this isn’t to say that all triathletes should lose weight. Many are lean already. Trying to cut weight when you’re already at, or even below, your optimal body weight isn’t a good idea as it can result in compromised health and poor training. You may already be at your best performance weight even though you’re heavier than most other triathletes.

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How heavy is too heavy?

Is 90kg too heavy to be a competitive Ironman triathlete? We really can’t say based just on weight because what if the athlete is 203cm tall? I once coached a young age-group triathlete like this who regularly qualified for Ironman Hawaii and finished in under nine-and-a-half hours. Despite his weight, he was skinny and fast.

So weight alone doesn’t tell you much. Body mass is a much better indicator, but a little complicated.
An easy way to think about your body mass is to find your weight-to-height ratio; it’s simple and effective. Calculate your ratio by dividing your weight in kilogrammes by your height in centimetres.

Competitive age-group male triathletes are generally about 0.38 to 0.41kgs per cm. High-performance age-group women triathletes are usually in the range of 0.32 to 0.35.

Eating less vs training more

If you want to lower your weight-height ratio, you need to consider if weight loss is really in your best interests. Some people, even when they have single-digit percent body fat, are still above the upper ratio limits for their heights due to heavy bone structure and muscle mass.

If, however, your health and performance could benefit from weight loss, it can be difficult to know how best to drop the last few kilogrammes, as studies on weight loss for serious athletes are rare. That said, one study did examine the issue in an interesting way, comparing eating less to exercising more to see which worked better in reducing excess body fat.

The scientists had endurance-trained men create a 1,000-calorie-per-day deficit for seven days, by either exercising more while maintaining their caloric intake or by eating 1,000 calories less daily while keeping exercise the same. (This is a huge daily deficit and not recommended outside of a controlled research study.)

With 1,000 calories of increased exercise daily – like running an extra eight miles or so each day – the exercise-more men averaged 0.75kg of weight loss in a week. The eat-less men who took in 1,000 fewer calories from food each day lost 2.15kg on average for the week – nearly three times as much.

But the weight-loss numbers don’t tell the whole story. The reduced-food-intake group in this study lost a greater percentage of muscle mass than the increased-exercise group and that’s an ineffective way to lose weight. If you’re lighter but you have less muscle to create power, the trade off isn’t necessarily good.

Eat less what?

Another study looked at how to reduce calorie intake and maintain muscle mass. Unfortunately, the study used sedentary women and not athletes as subjects, but the conclusions are still applicable to athletes.

Italian researchers fed two groups of women only 800 calories a day for three weeks (again, this is extreme
and not a recommended number for reducing weight). One group ate a relatively high-protein and low-carb diet while the other ate a low-protein and high-carb diet. Both ate 20% of calories from fat. The two groups lost similar amounts of weight, but the low-protein, high-carb group lost significantly more muscle mass. So if you plan to reduce weight by eating less, don’t cut back on protein as it may result in muscle loss.

How to lose excess weight for triathlons

When to lose weight

When one of the triathletes I coach needs to lose weight – usually less than 3kg – we do it in the early base period of the season by counting and reducing calories by about 10% per day. If we get to the ‘build one’ period – about 10 to 12 weeks before the first A-priority race – then it’s really too late and we need to move on to the more challenging race-like training.

The reason it’s too late is that losing weight puts the body under stress and compromises recovery. Those are never good things for an athlete, but better managed in the base period than in the build.

So there are three take-home messages here. Firstly, if losing a bit of excess weight is a healthy option then it’s more effective to cut calories than increase exercise volume – because it’s the base period, your volume may already be high. Secondly, protein must be kept at adequate levels when calories are reduced. Include protein in every meal and snack.

Finally, the best time in the season to lose weight is during the base period, as the closer you get to your A-priority race, the more detrimental calorie-cutting will be for recovery and performance.

Power to weight ratio

In 2011 Michael Weiss DNF’d at Kona eight miles into the run. He completed the 180km bike leg in 4:25:17, and thanks to SRM data, we note he climbed the 10km climb to Hawi in 20mins, recording an average speed of 30.5km/hr and power output of 338W. His vital stats are 6ft 3in tall and 79kg weight.

But what if he had been heavier? His weight of 79kg and 338W average power output translates to 4.27W/kg of body weight. But if he weighed 82kg, 338W would only give him 4.12W/kg. In order to maintain his speed
of 30.5km/hr he’d need to up his power output to 350W, and this would significantly deplete his energy resources.

Similarly, if his weight were to increase by a further 3kg to 85kg, he’d have to produce 363W in order to maintain his 4.27W/kg power output.

By being lighter, he needs less energy to get him up the climb, which is partly why he has the potential to run a fast marathon after such a long bike.

Note Although losing weight could theoretically improve his current power-to-weight ratio, because he’s already so lean, any weight loss would almost certainly come from muscle mass and not body fat.

For more on Joe Friel’s training methods, go to



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