Standardized Protocol For Monitoring Muscle Fatigue and Biomechanics In Amateur Cyclists Using Infrared Thermography

Summary

Cycling biomechanics relies on efficient muscle activation and core stabilization. Infrared thermography (IRT) offers non-invasive monitoring of muscle fatigue. This protocol establishes a standardized methodology for integrating IRT into biomechanical analysis, aiming to optimize performance and prevent injury in amateur cyclists through precise physiological monitoring.

Abstract

The use of stationary bikes has increased significantly, making physical activity more accessible to the general population. However, the lack of precise, non-invasive monitoring during training sessions can mask muscle imbalances and inefficient biomechanical patterns. These factors, subclinical in their initial stages, can lead to a high incidence of musculoskeletal injuries. Currently, exercise evaluation relies on the subjective perception of effort or conventional performance metrics, creating a critical gap in the early detection of physiological issues before they progress to chronic conditions. Given the crucial role of exercise in public health, it is imperative to implement sustainable evaluation strategies applicable to various fitness levels. In this context, infrared thermography (IRT) emerges as a promising alternative due to its ability to quantify skin surface temperature, a direct indicator of metabolic activity, thermoregulation, and blood flow. This project establishes a standardized methodological protocol using IRT to monitor the physiological response during cycling sessions in a non-athletic population. The application of this protocol revealed that standardized IRT can effectively detect subclinical thermal asymmetries and localized "hotspots" in joints (e.g., the knee at 32.8 °C) that are otherwise undetectable through subjective effort perception (Borg scale) or pedaling cadence monitoring. By systematically controlling environmental and subject-related variables, this research analyzes surface temperature distribution in the lower body to evaluate biomechanics and muscle fatigue. Specifically, the protocol facilitates the correlation between thermal patterns, fatigue levels, and pedaling cadence. This approach not only supports technological innovation in preventive medicine and public health but also lays the groundwork for an early detection tool capable of mitigating injury risks and optimizing the well-being of the population engaged in this activity.

Introduction

The biomechanics of cycling is a multifaceted discipline that integrates principles of human movement, muscle physiology, and energy transfer to optimize performance and prevent injury. At its core, cycling involves a cyclical alternation between the power phase—where the quadriceps, gluteal muscles, and gastrocnemius generate the majority of the propulsive force—and the recovery phase, during which the hamstrings and hip flexors facilitate the return of the leg to its initial position. Efficient energy transfer to the pedals is not only a function of lower limb muscle activation but also depends critically on core stabilization, which ensures biomechanica....

Protocol

The research protocol was conducted in accordance with the ethical principles of the Declaration of Helsinki. Due to the non-invasive and non-contact nature of infrared thermography, the safety of the participants was guaranteed throughout the monitoring process. All subjects provided written informed consent before any procedures were initiated, agreeing to the use of their physiological data for research purposes. The study followed the internal research guidelines of the Faculty of Engineering at the Universidad Autónoma de Querétaro, ensuring participant anonymity and data protection.

NOTE: To overcome the methodological incon....

Results

Cycling biomechanics:
Cycling biomechanics operate in the pedaling cycle. The Push Phase (Downward) generates the main force: Quadriceps (Rectus Femoris, Vastus Lateralis, Medialis, and Intermedius) are the primary motors, extending the knee and driving the pedal. The Glutes assist with hip extension, providing power and stability. The Calves (Gastrocnemius and Soleus) complete the transfer of force. The Pull and Recovery Phase (Upward) prepares the leg: Hamstrings flex the knee and pull the pedal up.......

Discussion

The research is based on two pillars: the effectiveness of Infrared Thermography (IRT) as a non-invasive tool for measuring physiological stress and the urgent need to standardize its methodological protocol. The justification for using IRT to assess fatigue in cycling is confirmed by a network analysis (Figure 2), which establishes Skin Temperature and Exercise Monitoring as central themes in the literature^1,2,4.

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Borg Scale	Borg Perception	RPE Scale 6-20	6-20 RPE scale used to correlate subjective fatigue with objective thermal asymmetries and subclinical hotspots.
Controlled Chamber	Internal Facilities	Physiology Lab	Environment maintained at 18 °C to 25 °C and 40–55% humidity to ensure stable skin temperature and minimize convective interference.
Data Log Sheets	Google	Google Forms (Digital Entry)	Standardized forms for recording anthropometric data (age, sex, BMI) and hydration status to control for individual thermoregulatory variables.
Informed Consent	Local Ethics Committee	Institutional Format	Documentation approved by the local Ethics Committee, ensuring adherence to the Declaration of Helsinki for non-invasive monitoring.
Infrared Camera	FLIR Systems	49001-2001	High-resolution (320 x 240 px) thermal imager set to ε = 0.98 to measure localized metabolic heat and thermal shifts (ΔT).
Marking Tools	BIC / Body Med	Skin Marker / Floor Tape	Skin-safe markers and floor tape used to fix camera-to-subject distance at exactly 100 cm and ensure consistent anatomical ROI alignment.
Stadiometer & Scale	SECA	763 (Digital Station)	Tools for recording height and body mass; necessary for calculating normalized power and documenting subject-specific physiological baselines.
Standardized Shorts	Nike	HV0411-010 / CZ9831-010	Black Lycra garments used to standardize skin emissivity and provide unobstructed access to the lower limb Regions of Interest (ROIs).
Stationary Bicycle	Monark	828E Ergomedic	Electromagnetic ergometer set to a fixed workload (e.g., 150 W) and constant cadence (80 RPM) to ensure steady-state metabolic heat production.
Stopwatch	Casio	HS-3V-1RET	Critical for timing the 15-min acclimatization period and ensuring IR capture occurs within 5 s post-exercise to avoid rapid thermal decay.
Thermometer-hygrometer	Control Company/Traceable	4040	Real-time monitoring device; used to input ambient temperature and humidity into the IR camera's object parameters for atmospheric correction.
Tripod	FLIR Systems	T197731	Stable support set at a 30 cm height and perpendicular angle (≈90°) to the lower extremities for repeatable image acquisition.