Kinetic changes in sweat lactate following fatigue during constant workload exercise

Abstract

It is useful to investigate various physiological responses induced by fatigue in athletes. Moreover, wearable noninvasive sensors, including sweat sensors, are compatible with fatigue evaluation because of their ease of use, and ability to measure repeatedly and continual data. This cross‐sectional study aimed to clarify how sweat lactate elimination curves obtained during constant workload exercise changed following fatigue. Seventeen recreationally trained males (average age, 20.6 ± 0.8 years) completed two consecutive constant workload exercise tests (at 25% peak power) with rest intervals; the participants were encouraged to perform Test 1 until exhaustion and Test 2 only for 10 min. Subjective fatigue (numerical rating scale with face rating scale), sweat lactate, and sweat rate were measured for 10 min in each test. Subjective fatigue was compared using the Wilcoxon signed‐rank test and time to each constant value between Tests 1 and 2 was compared using paired t‐test. Subjective fatigue significantly increased during Test 2 compared with that during Test 1. After Test 1, the sweat lactate elimination curve demonstrated a leftward shift, as proved by the significantly sooner observation of the peak and constant values of sweat lactate (2, 3, and 4 μA) (p < 0.01). Our preliminary results suggest that the sweat lactate elimination curve is different in the fatigue state. Further research may provide insight in the application of this curve to the evaluation for fatigue.

Realtime Monitoring of Local Sweat Rate Kinetics during Constant-Load Exercise Using Perspiration-Meter with Airflow Compensation System

“…It is possible that these present findings with LSR kinetics will contribute to interpreting the result obtained via real-monitoring biomarkers in sweat, which is beneficial for the evaluation of body status during exercise. The reason for this is that several analytes have the possibility to provide helpful information about body status by detecting the flexion point in a continually obtained value during exercise [ 9 , 10 , 11 , 33 ]. Further research or application in sports settings to the monitoring of analytes in sweat during constant-load exercise needs to interpret obtained results on the premise of the existence of two flexion points in LSR kinetics.…”

“…This is because sweat is readily accessible and contains important electrolytes, metabolites, amino acids, proteins, and hormones [ 7 , 8 ]. Particularly, sweat has the advantage of continuous profiling any alterations in body status during various forms of exercise, which is expected to contribute to a better understanding of unclear sports physiology—including real-time metabolism during swimming or ballgames—and be used in endurance evaluation [ 9 , 10 ] and determining fatigue status [ 11 ]. Unsurprisingly, the different types of sweat contain different concentrations of each component, likely due to sweat rate (SR).…”

Implications of the Onset of Sweating on the Sweat Lactate Threshold

“…The sweat rate and sweat lactate concentration were continuously monitored during incremental exercise. The sweat lactate was measured using a sweat lactate sensor chip (Grace Imaging Inc., Tokyo, Japan), which we developed and applied in several studies ( Figure S1 ) [ 7 , 8 , 17 , 18 ]. It is a type of electrochemical sensor that detects the potential generated by the redox reaction between the lactate and lactate oxidase.…”

“…Real-time sweat lactate values were automatically recorded in a connected application device (Grace Imaging Inc., Tokyo, Japan) via Bluetooth at 1 Hz. The sweat lactate value was quantified as the current value because the chip reacts with sweat lactate and generates an electric current [ 7 , 8 , 18 , 19 ]. The sLT was defined as the first significant increase in the lactate concentration in sweat above the baseline based on graphical plots [ 7 , 8 , 18 , 19 ].…”

“…In recent years, wearable sensing technology has been the focus of more precise evaluations of physiological responses in the body. We have developed a method to visualize the lactate dynamics of sweat during exercise in a noninvasive, simple, and real-time manner [ 7 , 8 ]. Furthermore, the sweat LT (sLT), assessed using sweat lactate dynamics, is consistent with the LT calculated from blood samples (bLT) and the VT [ 7 ].…”