A Novel Metric “Exercise Cardiac Load” Proposed to Track and Predict the Deterioration of the Autonomic Nervous System in Division I Football Athletes

Abstract

Current metrics like baseline heart rate (HR) and HR recovery fail in predicting overtraining (OT), a syndrome manifesting from a deteriorating autonomic nervous system (ANS). Preventing OT requires tracking the influence of internal physiological loads induced by exercise training programs on the ANS. Therefore, this study evaluated the predictability of a novel, exercise cardiac load metric on the deterioration of the ANS. Twenty male American football players, with an average age of 21.3 years and body mass indices ranging from 23.7 to 39.2 kg/m2 were included in this study. Subjects participated in 40 strength- and power-focused exercise sessions over 8 weeks and wore armband monitors (Warfighter Monitor, Tiger Tech Solutions) equipped with electrocardiography capabilities. Exercise cardiac load was the product of average training HR and duration. Baseline HR, HR variability (HRV), average HR, and peak HR were also measured. HR recovery was measured on the following day. HRV indices assessed included the standard deviation of NN intervals (SDNN) and root mean square of successive RR interval differences (rMSSD) Linear regression models assessed the relationships between each cardiac metric and HR recovery, with statistical significance set at α < 0.05. Subjects were predominantly non-Hispanic black (70%) and aged 21.3 (±1.4) years. Adjusted models showed that exercise cardiac load elicited the strongest negative association with HR recovery for previous day (β = −0.18 ± 0.03; p < 0.0000), one-week (β = −0.20 ± 0.03; p < 0.0000) and two-week (β = −0.26 ± 0.03; p < 0.0000) training periods compared to average HR (βetas: −0.09 to −0.02; p < 0.0000) and peak HR (βetas: −0.13 to −0.23; p < 0.0000). Statistically significant relationships were also found for baseline HR (p < 0.0000), SDNN (p < 0.0000) and rMSSD (p < 0.0000). Exercise cardiac load appears to best predict ANS deterioration across one- to two-week training periods, showing a capability for tracking an athlete’s physiological tolerance and ANS response. Importantly, this information may increase the effectiveness of exercise training programs, enhance performance, and prevent OT.

Internal or External Training Load Metrics: Which Is Best for Tracking Autonomic Nervous System Recovery and Function in Collegiate American Football?

“…Importantly, these relationships strengthened for all outcomes (R 2 0.19 to 0.52) across both acute and cumulative exposures. The relationships between ECL and ANS deterioration observed in the current study closely align with our previous work among collegiate football athletes that also showed the ECL metric exhibited strong predictive power of ANS deterioration for acute and cumulative exposures [ 3 , 13 ]. There are two significant concerns highlighted by these observations, specifically the poor predictive power of ACCEL.…”

“…Throughout each practice session, athletes wore the armband monitors on the posterior aspect of their right upper arm, fastened with an elastic band around the middle of the biceps muscle. The armband monitors (Warfighter Monitor TM (WFM), Tiger Tech Solutions, Inc., Miami, FL, USA) were previously validated in diverse populations including athletes [ 4 , 13 , 17 , 18 ] and were worn throughout the entire training session.…”

“…However, because these intensity estimates are derived from assumption-based equations and not necessarily applicable athletes [ 10 , 11 , 12 ], their accuracy in determining internal training load is significantly reduced. Exercise cardiac load (ECL) is a newly validated metric that provides a more accurate estimate of internal load using average training HR and session duration [ 13 ]. Recent work shows ECL outperforms commonly used HR-based metrics in estimating the influence of acute and cumulative internal training load on ANS recovery and function [ 3 ].…”

Exposures to Elevated Core Temperatures during Football Training: The Impact on Autonomic Nervous System Recovery and Function

“…Participants wore armband monitors equipped with temperature and electrocardiography (ECG) capabilities (Warfighter Monitor (WFM), Tiger Tech Solutions Inc., Miami, FL, USA). The WFM was previously validated in many subpopulations, including athletes [ 18 , 19 , 20 , 21 ]. Monitors were secured with an elastic band placed on the upper left arm and worn throughout exercise training sessions.…”

The effects of relaxation techniques following acute, high intensity football training on parasympathetic reactivation

“…The process for selecting training sessions ensured the pre-intervention exposures were similar in both duration and intensity. All athletes were exposed to the same exercises including strength- & power-focused resistance exercises, short-distance sprint intervals, aerobic training, and agility training ( 31 – 33 ). The average post-exercise HR and RR prior to the interventional trial were 158.6, 156.3, 161.3 bpm and 46.7, 46.7 and 42.6 breaths⋅min −1 for the mindfulness, rest, and no-intervention, respectively, indicating athletes were engaged in high intensity exercise ( 34 , 35 ).…”