Monitoring individual responses to training is an important key factor to prescribe to most effective training programs. Heart-rate variability (HRV) could be used for monitoring the training status of endurance athletes in order to detect the fatigue status and to assess the adaptation to training. This direct fatigue measuring method has been little used to prescribe or regulate exercise prescription. Moreover, it allows new possibilities for the training load prescription according to an athlete's status, the response to the training load, and the adaptation to training. Regardless HRV-guided training, the athlete performance could also be influenced by precompetitive mood and anxiety, which can also be reflected in the precompetitive HRV scores and the subjective effort perception.

Monitoring individual responses to training is an important key factor to prescribe to most effective training programs. A promising variable that is able to reflect positive or negative training adaptation is cardiac autonomic regulation. In general, a decreased training status is associated with a lower power output at the same submaximal heart rate and a slower heart rate recovery, whereas an increased training status is associated with an increased power output, the same submaximal heart rate, and a faster heart rate recovery.

In this line, heart-rate variability (HRV), which focuses on the variability of successive R-R intervals, have gained popularity in monitoring the training status of endurance athletes. This tool enables the detection of fatigue status and assesses the adaptation to training. After high intensity training or a short-term overreached period, there is a decrease in the resting HRV values, reflecting the effect of the fatigue. In addition, the increase of the performance after a training period is related to an increase in resting HRV. This direct fatigue measuring method has been little used to prescribe or regulate exercise prescription. Moreover, this HRV-guided training, also called day-to-day periodization, allows new possibilities for the training load prescription according to an athlete's status, the response to the training load, and the adaptation to training.

On the other hand, regardless HRV-guided training, the athlete performance could also be influenced by precompetitive mood and anxiety, which can also be reflected in the precompetitive HRV scores and the subjective effort perception. This is another interesting line that pretends to be clarified in this study.

Inclusion Criteria:

• Belonging to the Spanish Athletics Federation.
• Training and running in Spanish Athletics Federation contest during at least two years.
• Stay in the first third of the classification of the previous season last five races.

Exclusion Criteria:

• Cardiovascular pathologies.
• Parameters of blood pressure (BP) outside of normality.
• Respiratory problems diagnosed.
• Be in treatment of psychological problems.
• Regular consumption of drug (s) with direct or indirect effects on the Nervous System (e.g., anxiolytics, antidepressants, neuroleptics).
• Consumption of substances not permitted by the International Athletics Federation (IAF).
• Punctual consumption of medication that could alter the performance due to suffering some disease related to cardiorespiratory system (e.g., influenza).
• Do not attend at least the 90% of the workouts during the intervention.