Methods

BODY COMPOSITION

Body composition was estimated from bioelectrical impedance analysis. Measurements were performed at baseline and after four, eight, and 12 weeks. Total body resistance was measured by a bioelectrical impedance analyser (Akern-RJL BIA 101/S) in supine position as described previously.1 Fat free mass was estimated from the resistance index (RI), height, and age of the subject using the equations given by Shaefer et al(fat free mass (kg) = 0.15 + 0.65 × RI +  0.68 × age (years)).3 These equations have been established for the paediatric age range (3.9–19.3 years) by validating fat free mass predicted by bioelectric impedance analysis against a potassium dilution technique. However, these equations have not been evaluated for our population and no impedance predictions for Austrian children exist.

To assess the repeatability of our measurements, bioelectric impedance analysis was performed in 36 non-obese children with type I diabetes (22 boys, 14 girls; mean age, 12.3 years; SD, 2.6; range, 8.0–17.5) on two days spaced two weeks apart. The mean (SD) differences between the two measurements were 8.47 (30.44) ohms for resistance and 0.28 (1.64) kg for fat free mass.

DIETARY INTERVENTION

Both groups participated in the same dietary education programme. General dietary advice was given by group teaching. This included: energy requirements; relation of the different nutrients (protein, fat, and carbohydrates) in a balanced diet (20%/30%/50% of total energy); and the importance of fibre, vitamins, minerals, and fluids.

Energy intake was restricted to 4180 kJ/day in both groups; children older than 14 years were restricted to 5016 kJ/day (girls) and 5852 kJ/day (boys).

All participants received written information regarding an energy restricted, balanced diet, and detailed information of the daily allowance of each food component to avoid over consumption.

At each visit (at baseline; after four, eight, and 12 weeks; and after 6 and 12 months) each participant received dietary re-education on an individual basis.

TRAINING PROGRAMME

According to the recommendations of the committee on sports medicine,4 we established an individualised training programme. The use of proper technique and moderate intensity has been shown to be crucial in strength training with children.4The use of lighter loads than those used by adults,5 and proper supervision and instruction should help to minimise the risk of injury during participation in resistance training.6

Training sessions took place twice weekly in a public gym, with a duration of approximately 60–70 minutes for each session. After a warm up period on either a stationary bike, treadmill, or rowing ergometer, and a light stretch, each child performed two sets out of the following exercises: lying leg press; seated leg extensions and leg curls; seated bench press; lat pulldown to the front and long pulley row; seated shoulder press; triceps pushdowns and triceps extension at the dips machine; dumbbell biceps curls; calf raises seated and crunches. All exercises except dumbbell biceps curls were done on weightstacking machines (Galaxy-Sport, Carspach, France), in which resistance can be increased gradually.

The volume (number of sets performed during training sessions) increased after two weeks, working up to as many as three to four sets for each exercise. Intensity, expressed as a “10 repetition maximum” (10 RM)—the maximum load the child could perform 10 repeats with—was adapted during the time course of strength gain. Sets were pyramided: starting with a light set (50% of the 10 RM), with each following set using a slightly higher load. Only the last set was performed until muscle failure.

If the child was able to perform more than 10 repetitions in the final set, the resistance was increased for the next training session.

STATISTICAL ANALYSIS

Statistical analysis was performed using the software package SAS 6.10 for Windows (SAS Institutes, Cary, North Carolina, USA).7 Methods used were paired comparisons t test, Wilcoxon rank sum test, and Spearman’s correlation coefficient. p Values of 0.05 or less were considered significant.

ETHICAL CONSIDERATIONS

All patients and one parent gave fully informed written consent to participate in our study. The study was approved by the local ethics committee.