Many experts suggest that when losing weight around half your weight-loss will be lean mass and half will be body fat. The same experts also often suggest that you could lose even more lean mass if you ignore their advice and do an excessive amount of cardio.
However, a study published over 10 years ago shows that in preparation for competition, female bodybuilders used nearly 2 hours of cardio, 6-days a week and only 23% of their weight-loss was lean body mass. Are you curious to see what happened? Here’s a brief review of what the researchers did.
The study: Body composition changes in female bodybuilders during preparation for competition, by van der Ploeg, Brooks, Withers, Dollman, Leaney and Chatterton, in European Journal of Clinical Nutrition, 2001
What did the researchers do?
The researchers managed to track down five competitive female bodybuilders who agreed to have their body fat measured at 12-weeks out, 6-weeks out and just prior to a competition. They also agreed to provide details about their training routines during this period. The researchers also recruited five female athletes to serve as controls. They took the body fat measurements when the subjects were post-absorptive, were normally hydrated and had not exercised for 36 hours.
The researchers were keen to make sure that they produced reliable results. So they used a very sophisticated way of measuring body fat and lean body mass. They used an under-water weighing process called hydrodensitometry, where the volume of inspired air was measured by oxygen dilution and the densities of fat mass and lean mass were assumed to be constants across all subjects. They noted that the potential error in their measurements from this process was just 0.4% body fat.
The bodybuilders detailed that at 12-weeks out they spent 5.8 ± 1.1 days per week performing aerobic training for 344 ± 110 minutes (5 hours 44 minutes ± 1 hour 50 minutes). They also reported that approximately 4 weeks before the competition, they increased their time performing aerobic exercise to 590 ± 139 minutes (9 hours 50 minutes ± 2 hours 19 minutes). So in the second 6-week phase, the bodybuilders were performing almost twice as much cardio as in the first 6-week phase.
Weight training routine
The bodybuilders detailed that throughout the 12-week period, they performed weight-training 5.0 ± 1.2 days per week and for 342 ± 164 minutes (6 hours 4 minutes ± 2 hours 24 minutes). They used 2-3 sets of 10-12RM loads for each body part in addition to a single set of 6RM. Four of the five bodybuilders noted that they lost either some repetitions or some load over the 12 weeks on some or all exercises.
The researchers did not ask for the bodybuilders to complete diet diaries but four of the five bodybuilders stated that they did not reduce their energy intake at all over the 12 weeks, which was estimated as 6.41 ± 0.80 MJ per day (1,531 ± 194kcal per day).
Body fat percentage at 12-weeks out
The researchers noted that at the outset of the study, the body fat percentages of the bodybuilders and athletic female control subjects were very similar (17.8% vs. 17.4%). They also noted that these figures were similar to those reported in a large-scale study of female body fat percentages by Withers (1987), who found that body fat in 182 athletic females averaged 18.5%.
This is very interesting, as it suggests that when female bodybuilders are not preparing for competition, they are walking around at normal, athletic female body fat percentages.
Body fat percentage changes
The researchers found that the bodybuilders reduced their body fat percentage by an average of 5.6% over the 12-week period. Unsurprisingly, an average of 68% (range: 66 – 70%) of this loss occurred in the second 6-week period, when the bodybuilders were performing twice as much cardio. The following chart shows the reductions in body fat percentage for each bodybuilder:
Lean body mass changes
The researchers found that the bodybuilders reduced their lean body mass by an average of 1.34kg (3lbs) or 2.4% over the 12-week period. Despite the much greater loss of fat mass in the second 6-weeks than in the first 6-weeks (and double the amount of cardio), the amount of lean mass in both 6-week periods was almost identical, with an average of 51% (range: 38 – 61%) of the overall lean mass lost occurring in the second 6-week block. The following chart shows the reductions in lean body mass for each bodybuilder:
What did the researchers conclude?
The researchers concluded that bodybuilders at 12-weeks out displayed a similar level of body fat to other athletic females. They also concluded that the 12-week contest preparation period led to a 5.75kg (13lbs) reduction in body mass, made up of a 1.34kg (3lbs) reduction in lean mass and a 4.41kg (10lbs) reduction in fat mass. This means that the weight loss was 76.7% fat and 23.3% lean tissue, despite the relatively lean status at the outset.
The researchers also concluded that the weight and fat lost were greater in the second 6-week period than in the first. This was probably because in the second 6-week period, the bodybuilders performed an average of 9 hours 50 minutes cardio per week while they “only” performed an average of 5 hours 44 minutes per week in the first 6-week period.
What else is interesting?
It was also interesting that despite the much greater level of cardio and fat loss achieved in the second 6-week period, there were no differences in the amount of lean body mass lost in the two 6-week periods. It would appear from this small sample size that cardio of 1 hour 40 minutes, 6 days per week does not cause more muscle loss in female bodybuilders than half that amount.
If cardio was so effective at stripping off muscle mass, would we not have seen a much bigger difference between the first and second 6-week blocks? The following chart shows that while there was a huge difference between the amount of fat lost between blocks, there was a similar amount of lean mass lost in each block:
The only thing that was different between those two 6-week blocks was the amount of cardio. So we can see that there was an almost identical loss in lean body mass and a hugely increased amount of fat loss from the first 6-week block to the second week block. This suggests that cardio had a very significant effect on fat loss and a minimal impact on muscle loss.
What’s more, the female bodybuilders did not change their dietary intake at all during the 12-week period. They stuck at around 1,500 calories, worked harder and did more cardio. I guess there is something to be said for the whole calories-in-calories-out idea…
What are the practical implications?
For well-conditioned female bodybuilders:
So long as resistance training is continued, up to 2 hours of cardio per day does not necessarily lead to significant losses in muscle.
For anyone wanting to lose fat and retain muscle:
So long as resistance training is used, adding some cardio (the amount depending on current level of conditioning) in order to increase fat loss may be an effective alternative to cutting calories further and may not necessarily lead to additional losses in muscle mass.