Bodybuilding.com - Energy Restriction: The Effect It Has On The Female Muscular Function.

Printable page

Did you know?
Peripheral Heart Action (P.H.A.) is a system of training where you go from one exercise to another, with little or no rest, preferably alternating upper body and lower body exercises. Designed for cardiovascular training and to develop muscle mass.

Today I am going to present a study as it relates to female endurance athletes and the effects of a calorie restricted diet. Can this be a good thing?

Energy Restriction: The Effect It Has On The Female Muscular Function.

By: Shannon Clark

Many women who are hoping to lose a few pounds turn to energy restriction as a way to accomplish the caloric deficit needed to lose bodyweight. The normal protocol for this method is restricting calories to about 75% of maintenance level while continuing their normal workout programs. The one concern with this method however, is that on a calorie restricted diet, substrate utilization in the body often changes, which could cause a change in performance values.

In this article, I'll discuss a study (Belcastro, A., McCargar, L., McKenzie, D. & Parkes, S., 1998) where female endurance athletes were assigned to two groups, one that ate at maintenance, and one at 75% below for 2 weeks while continuing on with their normal exercise training program and the effects that this caloric restriction created.

The Study

When someone goes on a diet, their bodys' method of substrate utilization begins to change, which may alter muscle tissue structure and function due to a selective breakdown of functional muscle proteins. Often, this change increases the amount of fat oxidation, which is what one is hoping for when they go on a reduced calorie diet.

The Subjects

The 14 subjects that were used for this study had the following requirements: eumenorrhea, not currently following a therapeutic diet program, a body fat that was between 16 and 20%, a VO2 max level of at least 42 ml/kg/min, and were running at minimum, 30 km/week as well as participating in other cross training activities for at least 3 hours of the week (Belcastro et al., 1998).

VO2MAX CALCULATOR

Prior to the experiment, the researchers took baseline measurements for various muscle performance measures so they could be compared with after the caloric deficit was induced.

The First Four Days

While they were on this diet, if the women started seeing changes in their weight, their daily caloric allotment was altered so as to find their individual maintenance level, which was then used to determine the 25% calorie reduced diet.

Fourteen Day Testing Period

During the 14 day testing period, the subject's meals were weighed and measured to ensure accuracy and they were instructed to consume all the food given to them and only supplement the diet with noncaloric beverages.

Substrate Utilization

This technique monitors the concentration of oxygen and carbon dioxide in the air that the subject breathes out while in an enclosed space.

Muscular Function

leg extension

Click To Enlarge.
Leg Extensions.

The values that were recorded were both peak (highest torque obtained throughout the exercise) and average (average torque throughout the range of motion) torque (Belcastro et al., 1998).

The Results

The results of the study showed that after the 2 week period of being on the diet, the non-diet group (100% of caloric intake) had the same measurements for bodyweight, BMI and skinfolds, while the dieting group (75% of caloric intake) had significant decreases in these measurements.

BMI (BODY MASS INDEX) CALCULATOR

Weight:
Height In Inches:

Results
Body Mass Index

It should be noted as well that lean body mass did not significantly change throughout the study, thus showing that these women lost predominately fat mass. One interesting finding is that the dieting groups resting RQ was seen to be significantly lower than that of the non-dieting group post study and lower than it had originally been in the pre-study measurement testing.

This demonstrates the fact that going on a calorie reduced diet will cause your body to burn a greater percentage of it's overall daily calories from fat as compared to carbohydrates, thus changing substrate utilization.

In regards to muscle function, no significant differences were seen in overall muscle function between pre and post diet in either groups (Belcastro et al, 1998).

Eccentric & Concentric

On the concentric side of things, the 120 degree/sec measurement decreased in the dieting group and concentric peak torque for the non-dieting group increased at the 30 degree/sec measurement (Belcastro et al., 1998). While there were differences seen, as stated above, there were no major noticeable differences that would cause a huge decrease in performance level as a result of going on a short-term calorie reduced diet.

Conclusion

A few factors to keep in mind with regards to this study are the results that showed an increase in torque value could have been due to the training effect in the individual and not whether or not they were following the diet.

Additionally, since the diet only took place over 2 weeks, this may not have been enough time to fully determine the effects of following a reduced calorie diet over a longer period of time that is often required to lose a greater amount of weight.

If the subjects had continued with this diet for a greater duration, or if there had been more of a restriction, these results could have been significantly different.

So What Is The Take Home Message From This Study?

As long as the diet is properly balanced, this type of restriction appears to be a safe and effective method without risking athletic performance.

Reference:

Belcastro, A., McCargar, L., McKenzie, D., & Parkes, S. (1998). Effect of Energy Restriction on Muscle Function and Calcium Stimulated Protease Activity In Recreational Active Women. Canadian Society for Exercise Physiology, 23(3)

ShannonC_77@yahoo.ca