Associations between objective measures of performance-related characteristics and perceived stress in young cross-country skiers during pre-season training

Figures & data

Table 1. Characteristics of the participants (means ± SD).

	Males (N = 15)	Females (N = 14)
Age (yrs.)	17 ± 1	17 ± 1
Height (cm)	179.2 ± 6.6	167.6 ± 6.2
Body mass (kg)	70.7 ± 8.9	62.6 ± 5.0
VO2max (mL/kg/min)	66.1 ± 4.4	54.2 ± 2.1
Maximal heart rate (bpm)	199 ± 9	200 ± 6
Annual training (hrs.)	544 ± 65	557 ± 54

Figure 1. Timeline of the investigated study period.

Figure 2. Scores on the different items of the perceived stress test during the pre-season training period.

*Significant difference between males and females, p ≤ 0.05

Table 2. Sleep heart rate, duration and latency, perceived level of stress (PSS) and countermovement jump performance (CMJ) by the junior male and female cross-country skiers during the different months of pre-season training.

	August	September	October	November	Time Effect		Aug.- Sept.		Sept.- Oct.		Oct. - Nov.		Aug. - Nov.
	M, n = 10	M, n = 12	M, n = 11	M, n = 12
Sex	F, n = 9	F, n = 11	F, n = 14	F, n = 14	(df, df) F	P	%Δ	ES	%Δ	ES	%Δ	ES	%Δ	ES
Sleep HR (bpm)
M	51.7 ± 5.4	51.2 ± 5.2	51.3 ± 5.5	54.9 ± 6.8	(3, 28) 5.59	0.004*	−1.0	0.09	0.3	0.03	7.0	0.58	6.3	0.53
F	54.5 ± 5.1	53.6 ± 4.4	53.8 ± 5.5	54.5 ± 5.3	(3, 31) 0.95	0.431	−1.6	0.19	0.4	0.04	1.2	0.12	−0.1	0.01
Sleep duration (hrs)
M	8.5 ± 0.4	8.6 ± 0.7	8.9 ± 0.9	8.7 ± 0.8	(3, 28)1.36	0.274	1.3	0.19	3.5	0.38	−2.1	0.23	2.6	0.35
F	8.3 ± 1.1	8.1 ± 0.8	7.9 ± 1.2	8.7 ± 0.6	(3, 31) 2.23	0.105	−3.1	0.27	−2.0	0.16	9.5	0.81	4.0	0.37
Sleep latency (min)
M	27.3 ± 2.9	29.2 ± 7.9	26.9 ± 5.0	30.1 ± 7.0	(3, 28) 1.24	0.313	6.7	0.32	−8.0	0.35	11.8	0.52	10.0	0.51
F	33.2 ± 10.1	36.5 ± 10.5	29.7 ± 6.6	31.0 ± 8.9	(3, 31) 1.98	0.137	9.9	0.32	−18.7	0.78	4.4	0.17	−6.8	0.24
HRVPM (RMSSD)
M	55.1 ± 25.4	56.6 ± 21.7	57.4 ± 20.7	52.2 ± 16.0	(3, 28) 0.82	0.494	2.7	0.06	1.4	0.04	−8.9	0.28	−5.2	0.13
F	58.6 ± 22.0	65.8 ± 20.5	58.7 ± 25.7	69.0 ± 20.3	(3, 31) 0.87	0.467	12.4	0.34	−10.8	0.31	17.5	0.44	17.7	0.49
HRVAM (RMSSD)
M	69.0 ± 26.7	74.9 ± 25.8	69.2 ± 28.3	69.9 ± 26.6	(3, 28) 1.10	0.367	8.7	0.23	−7.7	0.21	1.0	0.02	1.3	0.03
F	72.2 ± 26.3	73.3 ± 30.1	77.1 ± 22.9	75.9 ± 20.9	(3, 31) 0.24	0.868	1.5	0.04	5.2	0.14	−1.5	0.05	5.1	0.16
PSS score**
M	10.4 ± 5.9	13.9 ± 9.3	14.3 ± 6.6	13.6 ± 6.5	(3, 23) 4.34	0.015*	34.3	0.46	3.0	0.05	−5.1	0.11	31.3	0.52
F	18.6 ± 11.1	20.6 ± 9.4	18.6 ± 6.1	21.4 ± 8.0	(3, 32) 1.51	0.231	10.9	0.20	−9.7	0.25	15.3	0.40	15.5	0.30
CMJ (cm)**^,***
M	35.3 ± 3.4	35.9 ± 3.1	38.7 ± 3.9	37.5 ± 4.3	(3, 22) 5.78	0.005*	1.6	0.17	7.7	0.80	−3.1	0.29	6.1	0.56
F	29.8 ± 3.2	29.7 ± 4.0	30.2 ± 3.6	30.2 ± 3.4	(3, 30) 0.48	0.698	−0.5	0.04	1.7	0.13	0.0	0.00	1.2	0.11

Also presented here are the within-sex changes over time according to the linear mixed-model (LMM), including the within-sex time effect F scores, degrees of freedom (df), p values, relative change (%Δ) from week to week and Hedge’s g effect size (ES).

*Significant effect of time (p < 0.05) on the linear mixed model (LMM) for each sex.

**Significant difference in LMM (p < 0.05) between the males and females.

***Significant time-sex interaction (p < 0.05) observed in LMM for all of the subjects combined.

Table 3. Submaximal running performance, heart rate (HR), blood lactate concentrations (Lac) and rate of perceived exertion (RPE) by the junior male and female cross-country skiers during the different months of pre-season training.

	August	September	October	Time Effect		Aug.- Sept.		Sept.- Oct.		Aug.- Oct.
	M, n = 11	M, n = 11	M, n = 9
Sex	F, n = 11	F, n = 12	F, n = 12	(df, df) F	P	%Δ	ES	%Δ	ES	%Δ	ES
HR (1% max)
M	77 ± 5	75 ± 7	71 ± 6	(2, 11) 0.59	0.569	−2.6	0.33	−5.3	0.61	−7.8	1.09
F	77 ± 4	71 ± 22	79 ± 4	(2, 18) 0.87	0.436	−7.8	0.38	11.3	0.51	2.6	0.50
HR 4% max)
M	90 ± 4	92 ± 6	88 ± 5	(2, 13) 0.78	0.480	2.2	0.39	−4.6	0.72	−2.2	0.44
F	91 ± 2	92 ± 2	93 ± 3	(2, 19) 2.87	0.082	1.1	0.50	1.1	0.39	2.2	0.78
Lac 1 (mmol/L)**
M	1.8 ± 0.6	1.8 ± 0.5	1.6 ± 0.6	1.24	0.320	−1.1	0.04	−10.4	0.33	−11.4	0.35
F	1.6 ± 0.5	1.8 ± 0.4	2.1 ± 0.5	7.55	0.004*	16.8	0.53	13.8	0.53	32.9	0.98
Lac 4 (mmol/L)
M	4.5 ± 1.7	5.1 ± 2.1	3.7 ± 1.9	(2, 13) 0.50	0.618	14.5	0.35	−28.4	0.74	−18.0	0.46
F	4.0 ± 1.4	5.2 ± 1.5	5.0 ± 1.4	(2,20) 4.00	0.034*	29.1	0.80	−4.2	0.15	23.6	0.67
RPE 1
M	10.7 ± 1.2	11.0 ± 1.5	11.8 ± 1.0	(2, 13) 1.72	0.217	2.5	0.20	6.8	0.59	9.5	0.91
F	11.6 ± 0.9	11.5 ± 1.3	11.7 ± 1.1	(2, 20) 0.99	0.907	−0.9	0.09	1.1	0.11	0.3	0.03
RPE 4
M	15.9 ± 1.5	16.1 ± 1.8	16.3 ± 1.0	(2, 13) 0.48	0.630	1.1	0.11	1.0	0.11	2.1	0.26
F	15.7 ± 1.7	16.1 ± 1.6	16.3 ± 1.6	(2, 20) 0.65	0.533	2.2	0.22	1.6	0.16	3.8	0.37

HR 1 = Percentage of maximal heart rate in stage 1 low-intensity running.

HR 4 = Percentage of maximal heart rate in stage 4 high-intensity running.

Lac 1 = Blood lactate concentration in stage 1, Lac 4 = Blood lactate concentration in stage 4.

RPE 1 = Rate of Perceived Exertion in stage 1; RPE 4 = Rate of Perceived Exertion in stage 4.

Also presented here are the within-sex changes over time according to the linear mixed-model (LMM), including the within-sex time effect F scores, degrees of freedom (df), p values, relative change (%Δ) from week to week and Hedge’s g effect size (ES).

*Significant effect of time (p < 0.05) on the linear mixed model (LMM) for each sex.

**Significant time-sex interaction (p < 0.05) observed in LMM for all of the subjects combined.

Figure 3. An example of individual changes during a pre-season training period for perceived stress scores (PSS) and rates of perceived exertion (RPE), percentages of maximal heart rate (%HRmax) and blood lactate concentrations during submaximal running in one male (a) and one female (b).

Table 4. Pooled regression estimates of PSS and variables associated with jump performance and their 95% confidence intervals.

	PSS score		Jump
	B	95% CI	B	95% CI
Intercept	28.58*	(0.29, 56.88)	43.49***	(30.44, 56.55)
Sex (F)	5.93*	(1.09, 10.77)	−6.05***	(−8.40, −3.69)
PSS score	-	-	−0.04	(−0.16, 0.09)
Sleep HR	0.17	(−0.25, 0.59)	−0.14	(−0.32, 0.04)
Sleep duration	−2.79**	(−4.95, −0.62)	0.40	(−0.78, 1.58)
Sleep latency	−0.03	(−0.29, 0.23)	−0.09	(−0.20, 0.01)
HRVAM	0.01	(−0.07, 0.09)	0.00	(−0.03, 0.04)

*p ≤ 0.05, **p ≤ 0.01, ***p ≤ 0.001.

HR = heart rate, HRV_AM = Morning nocturnal heart rate variability, PSS = perceived stress score.

Table 5. Pooled regression estimates of SRT variables and their 95% confidence intervals.

	Heartrate 1		Heartrate 4		Lactate 1		Lactate 4
	B	95% CI	B	95% CI	B	95% CI	B	95% CI
Intercept	0.85***	(0.41, 1.30)	0.87***	(0.67, 1.06)	0.74	(−2.21, 3.69)	8.64*	(0.91, 16.37)
Sex (F)	0.04	(−0.02, 0.10)	0.01	(−0.01, 0.04)	0.05	(−0.26, 0.36)	0.12	(−0.84, 1.97)
PSS Score	0.00	(−0.01, 0.00)	0.00	(0.00, 0.00)	−0.01	(−0.03, 0.01)	−0.02	(−0.08, 0.04)
Sleep HR	0.00	(0.00, 0.01)	0.00	(0.00, 0.00)	0.03	(−0.01, 0.06)	0.03	(−0.07, 0.14)
Sleep duration	0.00	(−0.04, 0.03)	0.00	(−0.01, 0.01)	−0.03	(−0.26, 0.20)	−0.62*	(−1.23, −0.02)
Sleep onset	0.00*	(−0.01, 0.00)	0.00	(0.00, 0.00)	0.00	(−0.02, 0.02)	0.01	(−0.05, 0.06)
HRV AM	0.00	(0.00, 0.00)	0.00	(0.00, 0.00)	0.00	(0.00, 0.01)	−0.01	(−0.03, 0.01)

*p ≤ 0.05, **p ≤ 0.01, ***p ≤ 0.001.

HR = heart rate.

HRV_AM = Morning nocturnal heart rate variability.

PSS = Perceived stress scale.

SRT = Submaximal running test.