Overtraining frequently compromises competitive performance in long-distance runners. A means for predicting overtraining or indicating the condition in time to take corrective action may help to improve the effectiveness of training.
Overtraining is characterised by a deregulated autonomic response of the cardiovascular system and therefore assessment of the autonomic nervous system may provide the basis for such a means. The authors examined whether alterations in the ratio of blood lymphocytes to neutrophils (L/N), which is believed to reflect the activities of sympathetic and parasympathetic sub-systems of the autonomic nervous system, was associated with performance in four female endurance runners over an eight-month period.
Blood was sampled monthly and analysed for the numbers of leucocytes, lymphocytes and neutrophils. The results were compared to performances in a series of 3000m time trials plus the runners’ subjective assessments of their condition. Those who performed well had lower L/N ratios before the time trials while those who did not showed higher L/N ratios.
Although the number of subjects in the study was small, the authors conclude that the L/N ratio shows a close relationship with performance and that an increased L/N ratio may be associated with fatigue, exhaustion or stress in endurance runners.