1. Pre-season Training And Cardiac Autonomic Indices In Elite Spanish Soccer Players
Daniel A. Boullosa1, Fábio Y. Nakamura2, Laurinda Abreu3, Rubén Crespo-Sánchez4, Eduardo Domínguez4, Anthony S. Leicht5.
1Universidade Católica de Brasília, Brasília, Brazil. 2Universidade Estadual de Londrina, Londrina, Brazil. 3Lavadores, Vigo, Spain. 4Universidade de Vigo, Pontevedra, Spain. 5James Cook University, Townsville, Australia.

2. Introduction
Soccer is an intermittent sport with requirements of both aerobic and anaerobic capacities (Helgerud et al. 2001; Krustrup et al. 2003; Rampanini et al. 2007; Sporis et al. 2009)
Laboratory based evaluations and field specific tests for training monitoring (Ziogas et al. 2011; Kalapotharakos et al. 2011)

3. Introduction Autonomic control of HR via HR variability (HRV) analysis
Most research in individual sports, mainly running (Kiviniemi et al. 2007; Manzi et al. 2009; Vesterinen et al. 2011)

4. Introduction
Buchheit et al. (2010) reported that daily changes in HRV (i.e. coefficient of variation) were significantly associated with maximal aerobic speed (MAS)

5. Introduction
Buchheit et al. (2012) showed a moderate relationship among baseline HRV changes in maximum sprint ability, acceleration, and repeated sprint ability (RSA)

6. Introduction
Buchheit et al. (2011) reported a relationship between exercising HR and performance improvements, with an incremented HRV, after an in-season training camp in the heat

7. Introduction
Night time HRV could be a more appropriate method as is NOT so influenced by factors like emotional stress, ambient temperature, or hydration status (Hynynen et al. 2006; Al Haddad et al. 2009; Nummela et al. 2010; Vesterinen et al. 2011; Boullosa et al. 2012)

8. Introduction
Thus, the aim of the current study was to evaluate changes in performance and cardiac autonomic control (HRV) in elite soccer players during their pre-season training regime

9. Methods Table 1 Players characteristics (n=8) Mean ± SD Age (years)
Mean ± SD
Age (years)
24.0 ± 4.0
Height (cm)
178.3 ± 4.9
Mass (kg)
72.7 ± 7.1
Body fat (%)
10.7 ± 0.6
Number of pre-season matches
6.8 ± 2.1
Pre-season playing time (min)
386.9 ± 93.8

10. Methods Physical Tests Autonomic Indices
Yo-Yo IR 1 → Total distance (m)
Gacon Test → Maximum Aerobic Speed (MAS; Km∙h-1)
Autonomic Indices
Night time HRV (~ 00:00 – 03:00 hrs)
RS800 (Polar Electro Oy, Finland)
Kubios HRV v2.0, University of Kuopio, Finland
R-R, HR, Time Domain, Frequency domain and Poincaré Plot.

11. Qualitative inference
Results
Table 2 Yo-Yo intermittent recovery level 1 (Yo-Yo IR1) and Gacon test parameters during the first (week 1) and last (week 8) week of the pre-season.
Magnitude of changes between weeks
Week 1
Week 8
%Δ; ±90% CL ES
Qualitative inference
Yo-Yo IR 1
Distance (m)
2475 ± 421
2600 ± 786
4.5; ±15.9
0.20
Unclear
HRmax (bpm)
191.2 ± 6.8
179.0 ± 7.5*
–6.3; ±2.9
1.68
Almost certainly
Gacon test
MAS (km h-1)
18.1 ± 1.1
18.2 ± 0.9
0.4; ±2.5
0.05
193.9 ± 4.6
188.9 ± 5.7†
–2.6; ±1.5
0.96
Very likely

12. Qualitative inference
Results
Table 3 Night-time heart rate variability measures during the first (week 1) and last (week 8) week of the pre-season.
Magnitude of changes between weeks
Week 1
Week 8
%Δ; ±90% CL ES
Qualitative inference
mean RR (ms)
1208 ± 198
1319 ± 178
11.1; ±21.5
0.59
Likely
mean HR (bpm)
51.0 ± 7.9
46.8 ± 6.1a
–8.1; ±7.3
0.45
SDNN (ms)
135 ± 50
163 ± 41*
31.7; ±32.9
0.61
Very likely
RMSSD (ms)
98.6 ± 81
116 ± 53
116; ±171
0.25
Unclear
LFnu
57.9 ± 20.7
52.4 ± 13.7b
–6.1; ±8.0
0.27
Possibly trivial
HFnu
42.1 ± 20.7
47.5 ± 13.7 c
29.3; ±29.8
0.26
LF/HF
2.3 ± 2.3
1.3 ± 0.7
–15.7; ±22.1
Possibly
SD1 (ms)
69.6 ± 57.1
82.6 ± 37.4
122; ±175
SD2 (ms)
174.2 ± 56.1
211.8 ± 53.1†
29.9; ±28.7
0.69
a p=0.088, b p=0.082, c p=0.086; *p=0.017, †p=0.023, different vs. Week 1.

13. Results Some correlations were detected between:
ΔHRmax and the change in Yo-Yo IR1 performance (r = – 0.688; p=0.059)
ΔHRmax during the Yo-Yo IR 1 was correlated with ΔRMSSD and ΔSD1 (ρ = 0.829; p=0.042, in both cases)

14. Results Some correlations were detected between:
HRV at week 1 and changes in HRV over the 8-week preseason (ρ= ; p<0.05).
Yo-Yo IR1 performance with night-time HR (r= –0.871, p=0.011) and HRV (SDNN, r=0.891; p=0.007; SD2, r=0.924, p=0.003) at week 8.

15. Results

16. Discussion
Overall (i.e. SDNN) and long-term HRV (i.e. SD2) were significantly improved after pre-season, with those players with greater baseline HRV exhibiting the lower HRV changes.
Differences with other studies probably as a result of the initial high physical fitness and the method of evaluation (Buchheit et al. 2010; 2011; 2012; Vesterinen et al. 2011).

17. Discussion
The unclear improvements in field performance tests could be related to the expected greater fitness over the subsequent weeks (i.e. delayed effect of training) (Issurin, 2009).
The lowering in HRmax could be mediated by neurocardiac adaptations; and also evidencing a reduced physiological capacity for better field performance (Zavorsky, 2000).

18. Discussion
The association between HRV and Yo-Yo IR1 performance only at week 8 may be related to a greater autonomic control both at rest and exercise (Boullosa et al. in press) which is coincident with the greater fitness.
This could explain discrepancies in previous cross-sectional studies (Buchheit & Gindre, 2006; Bosquet et al., 2007) that looked at associations between HRV and fitness parameters.

19. Discussion
The greater CVRMSSD at the end of pre-season despite no evident changes in RMSSD suggests a positive adaptation with an increased responsiveness of the autonomic nervous system to daily stress related disturbances (Hynynen et al. 2006; Boullosa et al. 2012; Plews et al. 2012).

20. TAKE HOME MESSAGE
Night time HRV could be a simple and appropriate tool for monitoring elite soccer players.
The variation of HRV (e.g. CVRMSSD) over a time window (e.g. 1 week) could be an efficient method for determining specific adaptations along the season.

21. THANKS! d_boullosa@yahoo.es