Body mass, fat mass, and lean body mass decreased in both boys and girls as hypothesized.
Weight loss per week was greater than generally recommended for outpatient treatment programs (0.25 to 0.50 kg/week). This can be partly explained by the intensive exercise program and the relatively low daily energy expenditure. Loss of fat free mass is most likely attributed to the restricted energy intake.3
For boys, the decrease in fat mass was associated with the decrease in body mass. In girls, however, the decrease in fat mass was not associated with the decrease in body mass. A definitive explanation for this difference cannot be given. Gender specific patterns regarding changes in body composition between girls and boys in the course of the program may be involved.
An important finding in this study was that anaerobic fitness of overweight and obese class I–III children and adolescents prior to the intervention period was not related to loss of body mass and changes in body composition. Only relative mean power was associated with the loss of fat mass in girls. This finding is in contrast with other studies, suggesting that subjects in good anaerobic fitness are more likely to lose weight and fat mass and to preserve lean body mass.9
The fact that only in girls mean power in W/kg was negatively correlated to loss of fat mass was surprising as both genders showed highly significant pre/post improvements in anaerobic fitness. The loss of lean body mass in relative terms was twice as high in boys as in girls. However, when expressed in absolute terms these losses were very small in both genders, an intended consequence of the subjects’ regular physical activity during the program.
Another main finding was that the decrease in body mass and fat mass were neither associated with the overall energy expenditure nor with the energy deficit during the 8-week program in both girls and boys. This finding incorporates and confirms the separate observations of previous investigators.21
Numerous acute responses and chronic metabolic adaptions to the dietary intervention and the physical activity program may be involved, including compensatory changes in resting and non-resting energy expenditure as well as sleeping and sedentary activity lipid oxidation rates.23
The improved satiety response to a meal and the also enhanced sensitivity of appetite control could be factors that should be considered.25
Moreover, recent research indicated that the macronutrient content of the energy-restricted diet might influence body compositional alterations following exercise regimens.26
Providing adequate amounts of protein during weight loss may be especially important in preserving lean body mass.27
Another factor that should be considered is the weight loss due to the loss of water. The depletion of water binding glycogen stores has a significant effect on the apparent weight lost and the degree of recidivism after a period of dieting.28
Fluid balance changes can thus dissociate the relationship between body mass and energy balance.29
Uncoupled respiration, protein turnover, and sympathetic nervous system activity may also contribute to increased energy expenditure and fat oxidation after exercise.20
The highly significant changes in body composition for boys and girls were in line with the literature.14
Weight loss was mainly attributed to loss of fat mass. As there are likely to be responders and non-responders in every exercise, a fat loss trial calculating mean fat loss alone hides the significant fat loss achieved by some individuals. Thus, it is feasible that high intensity fat loss programs are effective for producing a clinical decrease in fat (greater than 6% of fat mass).9
Lean body mass was preserved to a large degree in both genders due to the exercise interventions.
The improvements in anaerobic fitness when expressed in relative terms were impressive for both boys and girls. For instance, subjects kept their absolute mean power almost constant pre/post but lost a highly significant amount of weight (boys: −11.4% ± 1.6%, P
< 0.001; girls: −11.0% ± 2.8%, P
< 0.001) during the intervention. This resulted in also highly significant improvements (boys: 95.4% ± 109.1%, P
< 0.001; girls: 100.0% ± 119.9%, P
< 0.001) when expressed in relative figures. Peak power in absolute terms did not change significantly, but as with absolute mean power, relative mean power increased due to the loss of weight. In addition to metabolic adaptions, the improvements can also be partly explained by the acquisition of a certain degree of motor skillfulness.30
Moreover it is very likely that the sedentary subjects gained confidence in their bodies’ abilities during the program. Thus psychological factors may also play a role in the explanation of the enhanced performance.
The effectiveness of inpatient weight reduction programs seems to be undisputed and can be mainly explained by compliance.31
However, very limited evidence suggests that these improvements can be maintained over the 12 months following the end of treatment.32
The amount of absolute or relative weight change associated with behavioral interventions in these settings is generally modest and varies by intervention intensity and setting.32
The quality of the anthropometric data collected throughout the program, including the assessment of the subjects’ body composition by using the current gold standard dual-energy X-ray absorption, is a main strength of our study. A limitation of our study lies in the Wingate protocol itself. It is very short in duration, but highly demanding nonetheless, as unfit overweight and obese sedentary subjects have to tolerate substantial exercise-induced pain. It is therefore possible that some of the subjects did not go to their very limits, resulting in data of reduced significance. Furthermore, the measurements of dietary intake and energy expenditure are based on potentially error prone reports and calculations. The subject’s intake of medications was not assessed. Puberty status and menstrual cycle (if applicable) remained unregarded. Moreover, due to incomplete data in energy intake and training, the number of subjects was reduced from an initial pool of 122 to a total of 28 (9 girls, 19 boys).