Instruments and measurements

All anthropometric measurements were taken according to the ISAK protocol (International Society for the Advancement of Kinanthropometry) [23] accredited Level 1 ISAK anthropometrists and in accordance with assessments of anthropometric measurements [24]. Participants were measured with minimal clothing and no shoes. Body mass was measured to the 0.1 kg by making use of a SECA electronic scale. Body stature was measured as the perpendicular distance between the transverse planes of the Vertex and the inferior aspect of the feet, to 0.1 cm. The BMI was calculated by dividing body mass with stature (kg/m²). BMI values were classified according to International cut off points for thinness (grade1, 2, 3), overweight and obesity according to gender and age (2–18 years) [25, 26]. BMI values were classified according to International cut off points for thinness (grade1, 2, 3), overweight and obesity according to gender and age (2–18 years) [8, 25, 26]. The BMI classification for thinness, overweight and obesity for seven-year old boys (≤ 14.04; 17.92; 20.63), eight-year old boys (≤ 14.15; 18.44; 21.60), nine-year old boys (≤ 14.35; 19.10; 22.77), 10-year old boys (≤ 14.64; 19.84; 24.00), 11-year old boys (≤ 14.97; 20.55; 25.10), 12-year old boys (≤ 15.35; 21.22; 26.02) and 13-year old boys (≤ 15.84; 21.91; 26.84) were used. All other BMI values obtained not in the cut off values mentioned were classified as normal.

Sitting height was measured as the perpendicular distance between the transverse planes of the Vertex and the inferior aspects of the buttocks when seated, to 0.1 cm. Arm span was measured as the perpendicular distance between the dactylia on the left and right arms with the arms outstretched horizontally, to 0.1 cm.

The triceps and calf skinfolds measures were taken using an Innovare skinfold calliper and were recorded to the nearest 0.5 mm. The triceps skinfold was taken parallel to the long axis of the arm at the triceps skinfold site (posterior surface of the arm, in the mid-line, at the level of the Mid-acromiale-radiale landmark), while the medial calf skinfold measurement was taken vertically at the medial calf skinfold site (the point on the most medial aspect of the calf at the level of the maximum girth). All measurements were taken twice, and in the event that the first two measurements differed with more than 0.5 cm/kg for the body mass and stature, and 0.5 mm for skinfolds, a third measurement was taken. The first two skinfold measurements were used to calculate the average skinfold thickness, which was then used for data analysis. The sum of skinfolds consisted of triceps and calf skinfolds. These skinfold measurements were also used to calculate fat percentage, by making use of Slaughter et al. [27] fat percentage charts for boys. Fat percentage criteria classification was done for low adiposity (≤ 10 mm), normal adiposity (11–25 mm) and high adiposity (≥ 26 mm) [27].

Chronological age of the participant was calculated by subtracting the date of birth from the date of measurement, and then classified in one-year intervals, for example, seven-year-old boys would be classified from 6.5 to 7.49 years. Table 1 indicates the total number of participants per age group as well as the ranges for each age group. Estimated timing of maturity was defined by the timing of the adolescent growth spurt (a period in time in which a child experiences their fastest upward growth in stature during adolescence, also known as peak height velocity). The onset of growth spurt coincides also with the onset of maturity [18].

The Anthropometrical measurements of 7–13 year old rural boys (mean ± SD, range)

7.04 ± 0.29

6.51–7.49

8.06 ± 0.26

7.54–8.49

9.02 ± 0.30

8.52–9.47

9.97 ± 0.28

9.50-10.49

11.08 ± 0.27

10.53–11.49

11.92 ± 0.30

11.50-12.49

13.00 ± 0.29

12.51–13.49

22.89 ± 2.52

22.29–23.48

24.71 ± 2.68

24.13– 25.30

27.02 ± 4.79

26.04–28.01

29.43 ± 5.20

28.32–30.46

32.88 ± 4.92

31.90-33.85

35.28 ± 6.41

33.87–36.69

39.70 ± 6.95

38.08–41.33

119.32 ± 4.30

118.30–120.33

124.29 ± 4.69

123.26-125.32

128.97 ± 5.99

127.73–130.20

132.91 ± 5.74

131.78-134.05

138.31 ± 5.81

137.16-139.46

141.99 ± 7.22

140.40-143.58

149.29 ± 7.67

147.50-151.08

16.05 ± 1.28

15.75–16.35

15.98 ± 1.30

15.69–16.26

16.19 ± 2.10

15.76–16.62

16.58 ± 2.01

16.18–16.98

17.13 ± 1.84

16.76–17.50

17.39 ± 2.19

16.91–17.87

17.73 ± 2.03

17.20-18.27

6.79 ± 2.28

6.24–7. 32

6.82 ± 1.72

6.44–7.20

6.62 ± 3.02

6.00-7.25

7.24 ± 2.83

6.67–7.79

7.91 ± 3.56

7.21–8.62

8.35 ± 4.00

7.47–9.23

8.18 ± 4.07

7.24–9.13

6.90 ± 2.48

6.31–7.48

7.30 ± 2.24

6.82–7.80

7.21 ± 4.11

6.37–8.06

8.11 ± 3.98

7.32–8.90

8.99 ± 4.62

8.07–9.90

9.84 ± 5.45

8.64–11.04

9.58 ± 4.63

8.50-10.66

13.68 ± 4.29

12.76–14.70

14.12 ± 3.47

13.36–14.89

13.84 ± 6.84

12.43–15.25

15.35 ± 6.35

14.08–16.61

16.90 ± 7.69

15.38–18.42

18.20 ± 8.80

16.26–20.13

17.76 ± 8.13

15.87–19.66

9.34 ± 2.62

8.72–9.97

9.61 ± 2.19

9.15–10.08

9.44 ± 4.17

8.58–10.30

10.36 ± 3.88

9.59–11.13

11.31 ± 4.70

10.38–12.24

12.10 ± 5.37

10.92–13.23

11.84 ± 4.96

10.68-13.00

12.40 ± 0.25

12.33–12.45

12.91 ± 0.22

12.87–12.96

13.35 ± 0.32

13.28–13.42

13.78 ± 0.33

13.71–13.84

14.25 ± 0.34

14.19–14.32

14.62 ± 0.42

14.53–14.71

14.92 ± 0.47

14.81–15.03

5.35 ± 0.23

5.29–5.40

4.85 ± 0.25

4.80–4.91

4.32 ± 0.30

4.27–4.39

3.80 ± 0.36

3.72–3.87

3.16 ± 0.377

3.09–3.24

2.70 ± 0.44

2.60–2.79

1.92 ± 0.511

1.80–2.04

Estimated maturity timing was determined by means of Maturity offset (the age at which a child is expected to achieve PHV) for each participant. This estimation was done by making use of the equation of Mirwald et al. [24] as follows: Maturity Offset = -9.236 + 0.0002708·Leg Length and Sitting Height interaction − 0.001663·Age and Leg Length interaction + 0.007216·Age and Sitting Height interaction + 0.02292·Weight by Height ratio, where R = 0.94, R²= 0.891, and SEE = 0.592. Those participants who matured early were classified with a maturity offset less than − 0.50 (before maturity offset ) while children who fell between − 0.49 and 0.48 were classified as those who matured averagely (during maturity offset ), while boys with a maturity age of more than 0.49 were classified as those who matured late (after maturity offset) [28].