The goal of this observational study is to characterize autonomic, neuroendocrine, and peripheral neurochemical responses to maximal rowing exercise and early recovery in highly trained male athletes.

The main questions it aims to answer are:

• How do circulating concentrations of cortisol, testosterone, dopamine, serotonin, gamma-aminobutyric acid (GABA), and the testosterone-to-cortisol ratio change in response to maximal rowing exercise and during the first hour of recovery?
• How do autonomic cardiovascular parameters, including heart rate variability, blood pressure variability, and baroreflex sensitivity, change 3 hours after maximal exercise compared with baseline values?
• Do endocrine, peripheral neurochemical, and autonomic responses demonstrate similar or divergent recovery patterns following maximal exercise?

Participants will:

• Perform a maximal 6,000-m rowing ergometer test.
• Undergo venous blood sampling before exercise, immediately after exercise, and 1 hour after exercise recovery for assessment of endocrine and peripheral neurochemical markers.
• Undergo noninvasive cardiovascular and autonomic assessment using the Task Force Monitor System before exercise and 3 hours after exercise recovery.

This observational study was conducted to investigate physiological responses to maximal rowing exercise and subsequent recovery in highly trained male athletes. The study employed a repeated-measures design, allowing assessment of exercise-induced changes across multiple physiological systems during distinct phases of recovery.

Participants completed a maximal 6,000-m rowing ergometer test under standardized laboratory conditions. Biological and physiological measurements were collected before exercise and during recovery according to a predefined protocol. Venous blood samples were obtained at baseline, immediately after exercise, and after 1 hour of recovery. Noninvasive autonomic and cardiovascular assessments were performed using the Task Force Monitor System before exercise and after 3 hours of recovery. The protocol was designed to capture both immediate biochemical responses and delayed autonomic recovery following maximal exercise.

The study focused on endocrine, peripheral neurochemical, and autonomic cardiovascular regulation. Peripheral neurochemical markers were assessed from blood samples and interpreted as components of the peripheral physiological response to exercise rather than direct indicators of central nervous system activity.

Data collection was performed under controlled laboratory conditions using standardized procedures. All measurements were obtained by trained investigators using calibrated equipment. Data quality was verified through routine review of laboratory and physiological recordings. Implausible values and technical artifacts were identified and evaluated before statistical analysis.

The planned sample size was based on the availability of elite athletes meeting the inclusion criteria and the repeated-measures design of the study. Statistical analyses were conducted using repeated-measures approaches appropriate for longitudinal within-subject data. Data distribution was assessed prior to analysis. Parametric or non-parametric tests were applied as appropriate. Effect sizes were calculated to complement significance testing. Associations between selected physiological variables were explored using correlation analyses. Missing data were handled using complete-case analysis, with no imputation procedures applied.

Inclusion Criteria:

Highly trained rowers competing at national or international level Regular participation in structured rowing training Current sports medical clearance for maximal exercise testing Ability to complete a maximal 6,000-m rowing ergometer test Written informed consent to participate in the study

Exclusion Criteria:

Acute illness, infection, or injury before testing Any diagnosed cardiovascular, metabolic, neurological, endocrine, or inflammatory disorder Use of medications or supplements that could affect cardiovascular, endocrine, metabolic, or neurochemical responses Inability to complete the maximal rowing test Inability or refusal to provide blood samples Non-compliance with study procedures or pre-test instructions

Participants were recruited from the Polish National Rowing Team training at the Olympic Preparation Centre (COS OPO) in Wałcz, Poland.

Individual participant data sharing has not yet been determined. Future sharing of de-identified data will depend on institutional policies, ethical considerations, participant consent, and planned secondary analyses.