Predicting sickness during a 2-week soccer camp at 3600 m (ISA3600)

Abstract

Objectives: To examine the time course of changes in wellness and health status markers before and after episodes of sickness in young soccer players during a high-altitude training camp (La Paz, 3600 m).

Methods: Wellness and fatigue were assessed daily on awakening using specifically-designed questionnaires and resting measures of heart rate and heart rate variability. The rating of perceived exertion and heart rate responses to a submaximal run (9 km/h) were also collected during each training session. Players who missed the morning screening for at least two consecutive days were considered as sick.

Results: Four players met the inclusion criteria. With the exception of submaximal exercise heart rate, which showed an almost certain and large increase before the day of sickness (4%; 90% confidence interval 3 to 6), there was no clear change in any of the other psychometric or physiological variables. There was a very likely moderate increase (79%, 22 to 64) in self-reported training load the day before the heart rate increase in sick players (4 of the 4 players, 100%). In contrast, training load was likely and slightly decreased (-24%, -78 to -11) in players who also showed an increased heart rate but remained healthy.

Conclusions: A >4% increased heart rate during submaximal exercise in response to a moderate increase in perceived training load the previous day may be an indicator of sickness the next day. All other variables, that is, resting heart rate, heart rate variability and psychometric questionnaires may be less powerful at predicting sickness.

Keywords: Altitude; Cardiology prevention; Fatigue; Physiology; Soccer.

Figure 1

Individual and mean (±SD) values for the four sick players. Changes in resting heart rate, resting vagal-related heart rate variability (LnSD1), heart rate response to the 5 min submaximal run, rate of perceived exertion response to the 5 min submaximal run, total wellness and Lake Louise scores. Symbols indicate clear standardised changes compared with the day before sickness, with *, **, *** and **** standing for small, moderate, large and very large changes, respectively. Access the article online to view this figure in colour.

Figure 2

Mean daily training load (SD, upper panel) in all players who demonstrated a >4% increase in heart rate in response to the standardised submaximal exercise and became sick or not. Measures are reported over 4 days. The lower panel shows the changes in training load and exercise heart rate from 2 to 1 day prior to sickness for both groups of players. Numbers indicate standardised changes (90% CI) from 3 to 2 (training load) and 2 to 1 (heart rate) days before sickness, or difference in the change in training load between the two groups. The grey areas represent trivial between-group differences (training load) or within-group changes (heart rate).