Interrelationships among skeletal age, growth status and motor performances in female athletes 10–15 years

Figures & data

Figure 1. Estimated mediating effect of stature, body mass and estimated fat-free mass on the relationship between the standardised residuals of skeletal age on chronological age and performances of female athletes. Analysis based on model 80 (Hayes 2018).

Table 1. Descriptive statistics (means ± standard deviations) for chronological age, skeletal age, body size, proportions and composition, motor performance, training history and participation motivation for non-skeletally mature athletes in the two age groups, for all variables except skeletal age among the sample of skeletally mature athletes, and for all variables in the total sample of non-skeletally mature athletes.

	Female athletes
	N-SM		SM	Total sample of N-SM
Variables	10–12 years	13–15 years
	(n = 42)	(n = 38)	(n = 34)	(n = 80)
Chronological age (years)	12.1 ± 0.8	14.0 ±0.7^†	14.8 ± 0.7^‡	13.0 ± 1.2
Skeletal age, TW3 RUS (years)	12.2 ± 1.1	13.9 ± 0.8^†		13.0 ± 1.3
Body size
Stature (cm)	153.5 ± 8.0	157.8 ± 5.6^†	159.4 ± 5.7	155.5 ± 7.2
Body mass (kg)	45.7 ± 9.8	50.2 ± 8.4^†	52.7 ± 7.2	47.8 ± 9.4
Body proportions
Sitting height/stature ratio (%)	52.2 ± 1.3	52.7 ± 1.3	53.1 ± 1.0	52.4 ± 1.3
Bicristal/biacromial ratio (%)	74.2 ± 4.5	73.2 ± 5.0	72.9 ± 4.1	73.7 ± 4.7
Body composition
Fat mass (%)	20.9 ± 5.8	21.4 ± 6.1	22.8 ± 3.6	21.2 ± 5.9
Fat mass (kg)	10.0 ± 4.5	11.2 ± 5.5	12.1 ± 3.2	10.5 ± 5.0
Fat free mass (kg)	35.8 ± 6.3	39.0 ± 3.8^†	40.6 ± 4.9	37.3 ± 5.5
Motor performance
Flamingo balance (number of attempts)	13.6 ± 6.1	9.8 ± 5.7^†	11.5 ± 5.2	11.8 ± 6.2
Plate tapping (s)	13.8 ± 1.4	12.8 ± 1.4^†	12.2 ± 1.7	13.3 ± 1.5
Sit and reach (cm)	20.9 ± 7.3	26.0 ± 9.7^†	27.6 ± 6.6	23.3 ± 8.9
Standing long jump (cm)	144.4 ± 17.0	161.1 ± 21.2^†	157.6 ± 23.1	152.3 ± 20.7
Handgrip strength (kg)	20.8 ± 4.2	24.2 ± 3.8^†	25.8 ± 5.2	22.4 ± 4.3
Sit-ups (number in 30 s)	21.2 ± 3.6	23.1 ± 3.6^†	23.1 ± 3.3	22.1 ± 3.7
Bent arm hang (s)	7.3 ± 6.0	12.9 ± 12.0^†	14.4 ± 12.6	9.9 ± 9.7
Shuttle run, 10 × 5 m (s)	22.0 ± 1.6	21.4 ± 1.5	21.3 ± 1.4	21.7 ± 1.5
12-min run (m)	1871 ± 273	1999 ± 311	1957 ± 294	1932 ± 297
50-metre dash (s)	9.2 ± 0.8	8.6 ± 0.8^†	8.6 ± 0.6	8.9 ± 0.9
Counter movement jump (cm)	30.4 ± 10.0	29.7 ± 9.7	30.9 ± 4.9	30.1 ± 9.8
Training history
Years of training (years)	4.6 ± 1.3	5.1 ± 1.6	5.7 ± 1.5	4.9 ± 1.5
Training (h·wk^-1)	6.0 ± 3.8	8.2 ± 5.1^†	7.7 ± 3.6	7.0 ± 4.6
Participation motivation
Group activity (range 1–5)	3.8 ± 0.7	3.6 ± 0.5	3.5 ± 0.6	3.7 ± 0.6

N-SM, non-skeletally mature; SM, skeletally mature. ^†Significantly different (p < 0.05) from the 10–12-year-old group. ^‡Significantly different (p < 0.05) from the 13–15-year-old group.

Table 2. Summary of the percentages of variance explained by body size (step 1), proportions (step 2), training hours per week and participation motivation (step 3), and standardised residuals of skeletal age on chronological age (step 4) in each of the motor performances of female athletes 10–12 years and 13–15 years.

	Hierarchical regression^†
Dependent variables	ΔR^21(step 1)	ΔR^22(step 2)	ΔR^23(step 3)	ΔR^24(step 4)
10–12 years (n = 42)
Flamingo balance	20.5*	1.0	1.1	0.0
Plate tapping	2.2	0.3	0.3	0.1
Sit and reach	5.0	6.3	0.3	0.8
Standing long jump	3.7	8.8	1.7	0.0
Handgrip strength	40.7***	5.9	8.6	0.2
Sit-ups	1.8	5.1	1.2	0.0
Bent arm hang	15.1*	15.7*	4.4	0.2
Shuttle run, 10 × 5 m	1.1	1.7	8.1	1.1
12-min run	16.6*	7.1	12.3	0.4
50-metre dash	4.2	4.9	10.3	0.0
Counter movement jump	2.1	1.5	5.4	1.8
13–15 years (n = 38)
Flamingo balance	5.8	2.2	7.7	0.4
Plate tapping	0.2	15.2	6.3	5.8
Sit and reach	12.8	7.4	0.9	0.0
Standing long jump	13.6	1.8	9.0	0.1
Handgrip strength	20.8*	11.6	1.0	0.5
Sit-ups	18.9*	8.3	22.6**	0.1
Bent arm hang	23.1*	17.2*	3.2	2.8
Shuttle run, 10 × 5 m	24.6*	5.3	6.6	1.3
12-min run	33.8**	0.7	5.3	0.1
50-metre dash	22.0*	18.8*	2.3	1.3
Counter movement jump	9.0	0.4	1.7	2.8

^†Independent variables entered the model at step 1: stature and body mass; step 2: sitting height/stature ratio, bicristal/biacromial ratio; step 3: training (h·wk⁻¹) and participation motivation; step 4: standardised residuals of skeletal age on chronological age. ΔR²_i = change in R². *p < 0.05; **p < 0.01; ***p < 0.001.

Table 3. Summary of parallel and serial mediation effects of stature, body mass and estimated fat-free mass on the relationship between the respective standardised residuals of skeletal age on chronological age and motor performances in the total sample of female athletes 10–15 years (n = 76), controlling for years of training and training hours per week.

	Specific indirect effects^‡					Direct effect
Motor performance	1	2	3	4	5
	(a1b1)	(a2b2)	(a3b3)	(a1d31b3)	(a2d32b3)	c’
Flamingo balance	.11 (−0.04, .23)	.13 (−0.17, .52)	−0.001 (−0.06, .06)	−0.04 (−0.13, .03)	−0.17 (−0.52, .13)	.15 (−0.12, .43)
Plate tapping	.02 (−0.30, .19)	.04 (−0.65, .62)	−0.001 (−0.08, .07)	−0.04 (−0.19, .11)	−0.15 (−0.69, .50)	.36 (−0.12, .84)
Sit and reach	−1.91 (−4.20, −0.39)^†	−0.77 (−4.30, 3.13)	.01 (−0.84, .84)	.80 (−0.01, 2.23)	3.30 (−0.01, 7.28)	−0.82 (−3.38, 1.74)
Standing long jump	.38 (−2.30, 4.32)	−9.80 (−18.88, −1.94)^†	.03 (−2.37, 2.43)	2.38 (.27, 4.96)^†	9.77 (2.00, 19.10)^†	−4.00 (−9.82, 1.83)
Handgrip strength	−0.13 (−0.61, .45)	−0.74 (−2.07, .41)	.01 (−0.45, .48)	.47 (.11, .97)^†	1.94 (.74, 3.50)^†	.08 (−0.97, 1.12)
Sit-ups	−14.41 (−1006.14, 681.10)	−2176.59 (−4843.37, 69.92)	6.14 (−466.16, 488.43)	434.46 (8.31, 1034.53)^†	1781.35 (69.90, 4191.37)^†	−733.21 (−2177.72, 711.30)
Bent arm hang	−0.12 (−0.30, .09)	−1.45 (−2.07, −0.92)^†	−0.003 (−0.22, .20)	.23 (.07, .43)^†	.95 (.50, 1.51)^†	.04 (−0.34, .43)
Shuttle run, 10 × 5 m	−0.04 (−0.33, .16)	.96 (.30, 1.78)^†	−0.002 (−0.19, .14)	−0.15 (−0.37, −0.003)^†	−0.61 (−1.34, −0.03)^†	.07 (−0.41, .54)
12-min run	29.74 (−6.79, 85.89)	−21.40 (−355.45, −103.16)^†	.37 (−26.12, 27.63)	25.87 (1.72, 57.63)^†	106.09 (1.83, 228.14)^†	−34.26 (−112.43, 43.90)
50-metre dash	−0.02 (−0.20, .10)	.60 (.27, 1.07)^†	−0.002 (−0.12, .11)	−0.11 (−0.23, −0.02)^†	−0.46 (−0.90, −0.15)^†	.03 (−0.22, .27)
Counter movement jump	−0.11 (−0.26, −0.01)^†	−0.57 (−1.07, −0.24)^†	−0.002 (−0.11, .10)	.11 (.03, .23)^†	.46 (.18, .88)^†	.08 (−0.19, .34)

Values are point estimates and 95% bootstrap confidence intervals. ^†Statistically different from zero, as indicated by the 95% bootstrap confidence intervals. ^‡1, the specific indirect effect of X on Y through M₁ [SAsr → stature → motor performance]. 2, the specific indirect effect of X on Y through M₂ [SAsr → body mass → motor performance]. 3, the specific indirect effect of X on Y through M₃ [SAsr → fat free mass → motor performance]. 4, the specific indirect effect of X on Y through M₁ and M₃ in serial [SAsr → stature → fat free mass → motor performance]. 5, the specific indirect effect of X on Y through M₂ and M₃ in serial [SAsr → body mass → fat free mass → motor performance.

Hayes AF. 2018. Introduction to mediation, moderation and conditional process analysis: a regression-based approach. 2nd ed. New York: Guilford Press.

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Data availability statement

The data that support the findings of this study are available from the “Madeira Youth Athlete Study,” but restrictions apply to the availability of these data, which were used under licence for the current study, and thus are not publicly available. Data are, however, available from the authors upon reasonable request and with permission of Duarte Freitas ([email protected]), the PI of the “Madeira Youth Athlete Study.” Complete tables are also available on request from the corresponding author.