Effects of weight reduction on body composition, hormone concentrations and physical performance in female track and field jumpers during a preparatory and competition season
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Introduction. Weight reduction is common and generally accepted among obese people, but nowadays also a general practice among athletes. There are many reasons for athletes to reduce weight: to increase physical performance, to compete in a lower weight class or aesthetic reasons. The aim of this study was to follow the effects of a preparatory season (exercise, diet) on body composition, hormonal concentrations and physical performance in female track and field jumpers and follow those variables throughout summer’s competition season. Methods. Thirteen national level female Finnish track and field jumping event athletes volunteered to the study. The subjects were divided into a weight reduction (WR) group (n=7) (age 21.5 ± 2.0 years; height 1.74 ± 0.06 m; mass 61.6 ± 2.4 kg; fat 17.1 ± 3.0 %) or a control (C) group (n=6) (age 20.5 ± 1.6 years; height 1.72 ± 0.09 m; mass 60.9 ± 6.9 kg; fat 18.7 ± 3.7 %). All subjects underwent a medical screening done by a doctor. There were three measurement points in the study period. The subjects kept food, activity and training diaries five days before each measurement point and the menstrual cycle was followed throughout the whole study. Subjects’ history of injuries was also ascertained. After the first measurement, the subjects were divided into the WR and C groups. After the first measurements, the WR group was advised to reduce their energy intake to achieve the target weight. From the mid to post measurements, the aim was to follow how body composition, hormonal concentrations and physical performance were affected. The C group was advised to keep their diet similar and correct any noted faults. The food diaries were analysed using the AivoDiet nutrient-analysis software and energy expenditure of physical activity assessed using MET-values by Ainsworth et al. (2011). Dual-energy X-ray absorptiometry (DXA) was used to evaluate fat percentage, fat mass, bone mineral content and bone mineral density. Blood samples were drawn from the antecubital vein after an overnight fast for determining serum total testosterone, free testosterone, estradiol, cortisol, insulin, insulin-like growth factor-1, triiodothyronine and ferritin concentrations. Physical performance tests included a 20 m sprint running test with a flying start, a 30 m sprint running test with a standing start position, counter movement jump, squat jump with and without extra weight and reactive jump. Statistical analysis was done with IBM SPSS Statistics 24.0 and Microsoft Office: mac Excel 2011. Group mean values and standard deviations were calculated with Excel. Within the groups pre versus mid, mid versus post and pre versus post significances were achieved by one-way ANOVA with repeated measures. Independent-samples t-test and Mann-Whitney U test were used to achieve significances WR versus C. Pearson’s and Spearman’s correlations were used to get correlation coefficients. Results. Considering the WR group, the energy intake of the subjects during the weight reduction period was 1664 ± 251 kcal/day and they were in an energy deficit of 477 ± 218 kcal/day. Energy deficit was implemented by reducing the carbohydrate and fat intake. The protein intake remained similar throughout the study (about 2.0 g/kg/day). The body mass was slightly reduced by 1.3 ± 1.3 kg (p=0.179), the fat percentage by 2.2 ± 0.7 % (p=0.0003) and the fat mass by 1.5 ± 0.4 kg (p=0.001) without changes in lean mass, bone mineral content or bone mineral density. There were no changes in physical performance or hormonal variables. There were significant difference (13 days) between the groups in the menstrual cycle length (p=0.01) and the menstrual disturbances were more prevalent among the WR group. Bone stress injuries were also more prevalent among the WR group and there was a great drop out (n=4) in the physical performance tests in the post measurements due to that. The lower mid fat percentage led to faster 30 m sprint times (r=0.902, p=0.036). The reduced body mass correlated significantly with the increased cortisol concentrations during the weight loss period (r=-0.845, p=0.034) in the WR group. Conclusion. According to this study, gradual weight reduction (-477 ± 218 kcal/day, 0.3 kg/week) has no negative effects on physical performance. Implementing weight reduction with moderate energy deficit by reducing carbohydrate and fat intake while maintaining high protein intake, would seem to be justified. Women athletes are at a greater risk of a menstrual disturbances and developing bone stress injuries as well as other health problems such as low energy availability and compromised iron status, especially, when reducing weight. The awareness of the risk factors of stress injury development and how to prevent them should be important among women track and field athletes, their coaches and nutritionists. ...
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