The line between training and overtraining.
Athletics — and especially middle- and long-distance running — is the sport in which the overtraining syndrome was first systematically described in sports medicine. We explain what today's science shows — with a precise source — and where NESA realistically fits.
Athletics wrote the first chapter of overtraining research.
Decades before wearable HRV devices
Decades ago, coaches and sports physicians already described so-called “staleness” in competitive runners — an unexplained decline in performance despite maintained or increased load. It was on this foundation that sports medicine later built the modern understanding of the overtraining syndrome — years before wearable HRV devices existed.
Historical context, not a diagnostic criterion.
The joint consensus of the ECSS and ACSM remains the leading authoritative document on the topic.
The overtraining syndrome is a “prolonged maladaptation”, not ordinary fatigue.
A multidisciplinary expert group of the European College of Sport Science (ECSS) and the American College of Sports Medicine (ACSM) defines the overtraining syndrome (OTS) as a prolonged maladaptation to training load that disrupts the body's hormonal, biological and neurological regulatory mechanisms — with accompanying mood disturbances and a decline in sports performance.
The autonomic nervous system occupies a central place in this picture: the classic description of OTS includes a disturbed balance between the sympathetic and parasympathetic branches. In research built on this consensus framework, heart-rate variability (HRV) has become established as a sensitive, non-invasive early indicator of autonomic maladaptation — but the consensus position, confirmed by later reviews devoted specifically to HRV, is clear: HRV is a sensitive early signal, not a stand-alone diagnostic tool. It must be interpreted together with subjective wellness scales and performance data, not in isolation.
Source: Meeusen R, Duclos M, Foster C, Fry A, Gleeson M, Nieman D, Raglin J, Rietjens G, Steinacker J, Urhausen A (2013). “Prevention, diagnosis, and treatment of the overtraining syndrome: Joint consensus statement of the European College of Sport Science and the American College of Sports Medicine.” Medicine and Science in Sports and Exercise, 45(1):186–205. DOI: 10.1249/MSS.0b013e318279a10a.
Directed at the same autonomic system that overtraining throws out of balance.
NESA XSIGNAL® works with controlled microcurrents through the limbs, directed at the balance between the sympathetic and parasympathetic nervous system. This is exactly the system that the ECSS/ACSM consensus describes as disturbed in the overtraining syndrome — the thematic link is real.
The overtraining syndrome is a real clinical condition and remains in the hands of the sports physician. Recovery and adaptation are the work of the athlete's own nervous system — NESA supports the conditions in which it regains its rhythm, and gives the physician a measurable marker (HRV) for follow-up.
The general overview of NESA in sports medicine is available on the Sports medicine page.
In basketball players, and in sleep and HRV studies, NESA already has measured results — and we have every reason to expect them to apply to runners and athletes as well.
In professional basketball players in a randomised placebo-controlled trial (FC Barcelona, García et al., Frontiers in Physiology 2022) the NESA group showed a significantly lower nocturnal heart rate and less wakefulness during the night. In sleep studies, +20% REM phase and +32 minutes of total sleep duration were measured (Medina-Ramírez, Stresses 2024), as well as −11% nocturnal heart rate (García et al., Front Physiol 2022). In a pilot randomised trial, heart-rate variability (SDNN) improved significantly more with NESA (Melián-Ortíz et al., Brain Sciences 2025).
The common denominator is autonomic balance — exactly the system that the ECSS/ACSM consensus places at the centre of overtraining. That is why, in athletes under medical supervision, we start with HRV before and after the protocol.
NESA supports autonomic regulation — hand in hand with sports-medical assessment.
The overtraining syndrome is diagnosed and followed up by a sports physician — there, HRV, the training diary and clinical judgement work together.
In an athlete under medical supervision, NESA can be the part that supports autonomic balance — while the nervous system itself restores its rhythm.
Absolute contraindications: pacemaker and other active electrical implants, pregnancy, epilepsy — checked against the device IFU before every application.
If you are considering NESA as an additional element in the care of an athlete with signs of overtraining — treat this page as a starting point for a conversation. Diagnosis and the treatment plan remain entirely in the hands of the sports-medicine team.
The full overview of NESA in sports medicine.
Mechanism, protocols, documented results and applications of NESA in sport.
→Discuss the specific case with us.
For sports physicians, physiologists and coaches: we explain the mechanism of NESA, the available protocols and how to judge whether it is a suitable tool within the athlete's overall plan.
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