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The authors would like to acknowledge Humberto Aguirre Becerra for their critical reading of the manuscript.

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 Aut&#243;noma de Quer&#233;taro, ensuring participant anonymity and data protection.
NOTE: To overcome the methodological inconsistencies identified in previous research, the protocol proposed in this study is strictly aligned with international standards for clinical and sports thermography. Specifically, the parameters for subject preparation and environmental control follow the guidelines established by the International Academy of Clinical Thermology (IACT), the American Academy of Thermology (AAT), and the Glamorgan Protocol. Furthermore, technical settings such as emissivity and thermal strain assessment follow the ISO 9886 standards and the recommendations of the European Association of Thermology (EAT). The feasibility of this protocol was validated with 60 biomedical engineering students from the Universidad Aut&#243;noma de Quer&#233;taro, aged between 20 and 25 years, to ensure protocol adherence and baseline homogeneity. This specific population ensured high compliance with pre-test restrictions and provided a homogeneous physiological baseline to verify the consistency of the thermographic captures.
1. Subject preparation and environmental control (Replicability and demographic impact)
<ol>
	<li>Inclusion criteria and subject factors
	<ol>
		<li>Record the age and sex of each subject for analysis of age differences and sex effects.</li>
		<li>Record the height and mass of the subject for use in anatomical parameters.</li>
		<li>Administer the Borg Rating of Perceived Exertion (RPE) scale (6&#8211;20). Instruct the subject to point to the number that represents their current exertion level before and after the test to correlate physiological data with subjective fatigue.</li>
	</ol>
	</li>
	<li>Consumption restriction and skin preparation
	<ol>
		<li>Prohibit the subject from consuming alcohol and nicotine for 24 h prior to measurement.</li>
		<li>Prevent the subject from consuming caffeine and from engaging in intense exercise during the 3 h prior to the test.</li>
		<li>Instruct the subject not to apply creams, cosmetics, or ointments to the lower extremities during the 12 h prior to the test.</li>
		<li>Confirm that the subject is adequately hydrated and record this on the pre-test data sheet.</li>
		<li>Use a clinical scale to record body mass before the test. Ask the subject to consume 300 mL of water 30 min before the session to ensure a standardized baseline hydration state.</li>
	</ol>
	</li>
	<li>Standardization of clothing and posture
	<ol>
		<li>Instruct the subject to completely undress the lower extremities of the body.</li>
		<li>Provide standardized cycling shorts (black Lycra with no visible seams).</li>
	</ol>
	</li>
	<li>Standardization of environmental and resting conditions
	<ol>
		<li>Place a digital thermo-hygrometer 1 m from the subject at a height of 1 m. Verify that the ambient temperature is between 18&#8211;25 &#176;C and the relative humidity is between 40% and 55%. Record these values every 5 min in a spreadsheet.</li>
		<li>Ensure that there are no direct drafts, exposure to sunlight, or sources of heat/cold that could influence thermoregulation.</li>
		<li>Perform a 15 min static, seated rest period for acclimatization to environmental conditions.</li>
		<li>Place the subject on the stationary bicycle in the required posture.</li>
	</ol>
	</li>
</ol>
2. Configuration and acquisition of thermographic images
<ol>
	<li>Open the thermal camera&#39;s internal settings menu. Navigate to Object Parameters and manually enter 0.98 for emissivity (&#949;). Set the Reflected Apparent Temperature to match the ambient temperature measured in step 1.4.1.
	<ol>
		<li>Use the infrared thermograph (IRF) thermal camera with a minimum resolution of 320 x 240 pixels.</li>
		<li>Set the emissivity (&#949;) to 0.98 for the surface of human skin.</li>
		<li>Use a laser distance meter or a physical measuring tape to place the tripod exactly 100 cm from the lateral plane of the bicycle&#39;s crankset. Mark the tripod leg positions on the floor with adhesive tape to ensure zero displacement between captures.</li>
		<li>Enter the relative humidity of the environment in the instrument settings.</li>
		<li>Set the atmospheric temperature of the laboratory and enter the external temperature.</li>
	</ol>
	</li>
	<li>Anatomical positioning and acquisition.
	<ol>
		<li>Place the thermograph on a tripod and set the camera height to 30 cm above the floor.</li>
		<li>Position the lens at a perpendicular angle (&#8776;90&#176;) to the lower end of the subject.</li>
		<li>In the thermal analysis software, select the Polygon/Rectangle ROI tool. Click and drag to delineate a 10 x 5 cm box over the Rectus Femoris (midway between the anterior superior iliac spine and the patella). Click Calculate to extract the Mean Temperature (Tmean).</li>
	</ol>
	</li>
	<li>Measurement point protocol
	<ol>
		<li>Capture the thermographic image immediately after completing the 15 min rest period.</li>
		<li>To ensure capture within 5 s, have the researcher stand behind the camera with the focus pre-set. At the signal &#34;Stop pedaling&#34;, extend the dominant leg to a 6 o&#39;clock position; immediately press the Capture/Freeze button on the camera trigger.</li>
		<li>Post-exercise recovery: Capture the third thermographic image 10 min after the exercise is completed.</li>
	</ol>
	</li>
</ol>
3. Exercise protocol execution
<ol>
	<li>Set the stationary bicycle to Ergometer Mode with a fixed workload of 150 W (adjusting for the subject&#39;s weight if normalized power is required).</li>
	<li>Place a digital metronome or use the bicycle&#39;s integrated console to enforce a constant cadence of 80 RPM. Instruct the subject to maintain this pace within a &#177;5 RPM margin to ensure a steady-state thermoregulatory response.</li>
	<li>Verify that the thermal camera is set to a Standard recording mode with a temperature range of 20 &#176;C to 45 &#176;C and an emissivity of 0.98.</li>
</ol>
4. Data analysis and standardization
<ol>
	<li>Calculate the thermal shift (&#916;T) using the formula: &#916;T = Tpost - Tpre. Perform this calculation for both the dominant and non-dominant limbs to determine thermal asymmetry (&#916;Tasymmetry = |Tright - Tleft|)</li>
	<li>Avoid manipulating or cropping the original thermographic image.</li>
	<li>Preserve the initial image resolution and complete metadata for analysis.</li>
</ol>

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<li>Shakhih, M. F. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Non-obstructive+monitoring+of+muscle+fatigue+for+low+intensity+dynamic+exercise+with+infrared+thermography+technique%5BTitle%5D)+AND+%22Med+Biol+Eng+Comput%22%5BJournal%5D)">Non-obstructive monitoring of muscle fatigue for low intensity dynamic exercise with infrared thermography technique.</a> Med Biol Eng Comput. 59, 1447-1459 (2021).</li>
<li>Li, N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Non-invasive+techniques+for+muscle+fatigue+monitoring%3A+A+comprehensive+survey%5BTitle%5D)+AND+%22ACM+Comput+Surv%22%5BJournal%5D)">Non-invasive techniques for muscle fatigue monitoring: A comprehensive survey.</a> ACM Comput Surv. 56 (9), 221-221 (2024).</li>
<li>Clarys, W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Thermography+in+bike+fitting%3A+A+literature+review%5BTitle%5D)+AND+%22Sensors+%28Basel%29%22%5BJournal%5D)">Thermography in bike fitting: A literature review.</a> Sensors (Basel). 25 (8), 2356(2025).</li>
<li>Quesada, J. I. P. <a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=author%3aQuesada%2C+JIP+%22Application+of+Infrared+Thermography+in+Sports+Science%22">Application of Infrared Thermography in Sports Science</a>. , Springer. Cham. (2017).</li>
<li>Hadžić, V., Širok, B., Malneršič, A., Čoh, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Can+infrared+thermography+be+used+to+monitor+fatigue+during+exercise%3F+A+case+study%5BTitle%5D)+AND+%22J+Sport+Health+Sci%22%5BJournal%5D)">Can infrared thermography be used to monitor fatigue during exercise? A case study.</a> J Sport Health Sci. 8 (1), 89-92 (2019).</li>
<li>Hu, C., Du, N., Liu, Z., Song, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Can+infrared+thermal+imaging+reflect+exercise+load%3F+An+incremental+cycling+exercise+study%5BTitle%5D)+AND+%22Bioengineering%22%5BJournal%5D)">Can infrared thermal imaging reflect exercise load? An incremental cycling exercise study.</a> Bioengineering. 12 (3), 280-280 (2025).</li>
<li>Verderber, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Assessment+of+alternative+metrics+in+the+application+of+infrared+thermography+to+detect+muscle+damage+in+sports%5BTitle%5D)+AND+%22Physiol+Meas%22%5BJournal%5D)">Assessment of alternative metrics in the application of infrared thermography to detect muscle damage in sports.</a> Physiol Meas. 45 (9), 095014-095014 (2024).</li>
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<li>Sheng, X., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Toward+an+integrated+multi-modal+sEMG%2FMMG%2FNIRS+sensing+system+for+human-machine+interface+robust+to+muscular+fatigue%5BTitle%5D)+AND+%22IEEE+Sens+J%22%5BJournal%5D)">Toward an integrated multi-modal sEMG/MMG/NIRS sensing system for human-machine interface robust to muscular fatigue.</a> IEEE Sens J. 21, 3702-3712 (2021).</li>
<li>Qu, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Continuously+monitoring+of+muscle+fatigue+based+on+a+wearable+micromachined+ultrasonic+transducer+probe%5BTitle%5D)+AND+%22Sens+Actuators+A+Phys%22%5BJournal%5D)">Continuously monitoring of muscle fatigue based on a wearable micromachined ultrasonic transducer probe.</a> Sens Actuators A Phys. 365, 114892-114892 (2024).</li>
<li>Al-Mulla, M., Sepulveda, F., Colley, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((A+review+of+non-invasive+techniques+to+detect+and+predict+localised+muscle+fatigue%5BTitle%5D)+AND+%22Sensors+%28Basel%29%22%5BJournal%5D)">A review of non-invasive techniques to detect and predict localised muscle fatigue.</a> Sensors (Basel). 11, 3545-3594 (2011).</li>
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<li>Guo, W., Sheng, X., Zhu, X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Assessment+of+muscle+fatigue+based+on+motor+unit+firing%2C+muscular+vibration+and+oxygenation+via+hybrid+mini-grid+sEMG%2C+MMG%2C+and+NIRS+sensing%5BTitle%5D)+AND+%22IEEE+Trans+Instrum+Meas%22%5BJournal%5D)">Assessment of muscle fatigue based on motor unit firing, muscular vibration and oxygenation via hybrid mini-grid sEMG, MMG, and NIRS sensing.</a> IEEE Trans Instrum Meas. 71, 1-10 (2022).</li>
<li>Quesada, J. I. P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Relationship+between+skin+temperature+and+muscle+activation+during+incremental+cycle+exercise%5BTitle%5D)+AND+%22J+Therm+Biol%22%5BJournal%5D)">Relationship between skin temperature and muscle activation during incremental cycle exercise.</a> J Therm Biol. 48, 28-35 (2015).</li>
<li>Formenti, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Dynamics+of+thermographic+skin+temperature+response+during+squat+exercise+at+two+different+speeds%5BTitle%5D)+AND+%22J+Therm+Biol%22%5BJournal%5D)">Dynamics of thermographic skin temperature response during squat exercise at two different speeds.</a> J Therm Biol. 59, 58-63 (2016).</li>
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The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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 literature1,2,4.
<p class="...

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&#8212;where the quadriceps, gluteal muscles, and gastrocnemius generate the majority of the propulsive force&#8212;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 biomechanical efficiency and minimizes compensatory movements that could predispose the cyclist&#160;to injury1,2,3.
Currently, researchers are focusing on the assessment of muscle activation patterns, fatigue, and thermoregulatory responses during cycling3,4,5. This interest is due to the recognition that muscle fatigue is a complex phenomenon, impairing performance and increasing injury risk, and that its early detection and management are essential for both elite and recreational cyclists2,6. Among the array of available assessment tools, infrared thermography (IRT) has been established as a promising, non-invasive technique for monitoring muscle activity and fatigue5. IRT enables the visualization of skin temperature changes, which may reflect underlying muscle activation and thermoregulatory processes during exercise that have a direct effect on athletes&#39; metabolism5,7.
Despite its potential, the application of IRT in cycling biomechanics research and practice faces several methodological challenges. While some standard operating procedures (SOPs) have been proposed in general sports and clinical contexts8,9, there is a recognized need for further refinement of existing protocols to address the unique physiological and convective cooling demands of amateur cycling7,10. The variability in environmental conditions, inconsistencies in subject preparation, and the lack of consensus regarding the selection of anatomical regions of interest have limited the reproducibility and comparability of findings across studies1,5,7,9. These limitations underscore the need for rigorous methodological frameworks to harness the full potential of IRT in the context of cycling7,10,11,12.
The literature reveals that the main thematic axes in this field include exercise physiology, IRT, skin temperature monitoring, exercise performance, and thermoregulation2,5,7. Studies have demonstrated significant correlations between skin temperature and muscle activation parameters, such as those obtained via surface electromyography (sEMG), suggesting that IRT can serve as a surrogate marker for muscle fatigue during dynamic exercise5. However, external factors such as perspiration, ambient temperature, and individual differences in thermoregulatory capacity could influence thermographic results, necessitating careful control and reporting of experimental conditions7.
Likewise, advances in non-invasive muscle fatigue monitoring have expanded beyond IRT to include techniques such as sEMG, mechanomyography (MMG), near-infrared spectroscopy (NIRS), and ultrasound imaging13,14,15,16,17. Each modality offers unique insights into muscle function: sEMG quantifies electrical activity during contraction, MMG captures mechanical vibrations, NIRS assesses muscle oxygenation, and ultrasound visualizes muscle deformation. The integration of IRT into this multi-modal landscape holds particular promise for cycling, where continuous, non-contact monitoring is advantageous. IRT can complement other modalities by providing spatially resolved, real-time data on skin temperature distribution, which may reflect localized muscle activation, asymmetries, and potential sites of overuse or injury14,18.
To overcome the methodological inconsistencies identified in previous research, the protocol proposed in this study is strictly aligned with international standards for clinical and sports thermography. Specifically, the parameters for subject preparation and environmental control&#8212;such as the restriction of stimulants and physical activity, and the use of standardized acclimatization periods&#8212;are based on the guidelines established by the International Academy of Clinical Thermology (IACT), the American Academy of Thermology (AAT), and the Glamorgan Protocol8. Furthermore, the environmental and technical settings, including emissivity and thermal strain assessment, follow the ISO 9886 standards and the recommendations of the European Association of Thermology (EAT). By integrating these established regulations, this study ensures that IRT measurements are a reliable reflection of physiological responses, providing a robust framework for monitoring muscle fatigue and biomechanics in recreational cyclists.
Nevertheless, the successful application of IRT in cycling biomechanics requires the establishment of standardized methodologies. This includes the definition of pre-exercise acclimatization periods, control of ambient temperature and humidity, consistent subject preparation, and the precise delineation of anatomical regions of interest for thermal analysis5,7. Furthermore, the development of robust data analysis protocols will enhance the interpretability and utility of IRT data5.
The present study addresses these gaps by proposing and validating a comprehensive methodological framework for the integration of IRT into biomechanical analysis in recreational cyclists. By systematically controlling for environmental and subject-related variables, and by correlating thermal data with established markers of muscle activation and fatigue, this approach aims to optimize the monitoring of muscle fatigue, contribute to injury prevention, and enhance performance outcomes2,5,7,14.

<table><tbody><tr><td>Borg Scale</td><td>Borg Perception</td><td>RPE Scale 6-20</td><td>6-20 RPE scale used to correlate subjective fatigue with objective thermal asymmetries and subclinical hotspots.</td></tr><tr><td>Controlled Chamber</td><td>Internal Facilities</td><td>Physiology Lab</td><td>Environment maintained at 18 &amp;deg;C to 25 &amp;deg;C and 40&amp;ndash;55% humidity to ensure stable skin temperature and minimize convective interference.</td></tr><tr><td>Data Log Sheets</td><td>Google</td><td>Google Forms (Digital Entry)</td><td>Standardized forms for recording anthropometric data (age, sex, BMI) and hydration status to control for individual thermoregulatory variables.</td></tr><tr><td>Informed Consent</td><td>Local Ethics Committee</td><td>Institutional Format</td><td>Documentation approved by the local Ethics Committee, ensuring adherence to the Declaration of Helsinki for non-invasive monitoring.</td></tr><tr><td>Infrared Camera</td><td>FLIR Systems</td><td>49001-2001</td><td>High-resolution (320 x 240 px) thermal imager set to &amp;epsilon; = 0.98 to measure localized metabolic heat and thermal shifts (&amp;Delta;T).</td></tr><tr><td>Marking Tools</td><td>BIC / Body Med</td><td>Skin Marker / Floor Tape</td><td>Skin-safe markers and floor tape used to fix camera-to-subject distance at exactly 100 cm and ensure consistent anatomical ROI alignment.</td></tr><tr><td>Stadiometer &amp;amp; Scale</td><td>SECA</td><td>763 (Digital Station)</td><td>Tools for recording height and body mass; necessary for calculating normalized power and documenting subject-specific physiological baselines.</td></tr><tr><td>Standardized Shorts</td><td>Nike</td><td>HV0411-010 / CZ9831-010</td><td>Black Lycra garments used to standardize skin emissivity and provide unobstructed access to the lower limb Regions of Interest (ROIs).</td></tr><tr><td>Stationary Bicycle</td><td>Monark</td><td>828E Ergomedic</td><td>Electromagnetic ergometer set to a fixed workload (e.g., 150 W) and constant cadence (80 RPM) to ensure steady-state metabolic heat production.</td></tr><tr><td>Stopwatch</td><td>Casio</td><td>HS-3V-1RET</td><td>Critical for timing the 15-min acclimatization period and ensuring IR capture occurs within 5 s post-exercise to avoid rapid thermal decay.</td></tr><tr><td>Thermometer-hygrometer</td><td>Control Company/Traceable</td><td>4040</td><td>Real-time monitoring device; used to input ambient temperature and humidity into the IR camera&#039;s object parameters for atmospheric correction.</td></tr><tr><td>Tripod</td><td>FLIR Systems</td><td>T197731</td><td>Stable support set at a 30 cm height and perpendicular angle (&amp;asymp;90&amp;deg;) to the lower extremities for repeatable image acquisition.</td></tr></tbody></table>

standardized protocol for monitoring muscle fatigue and biomechanics in amateur cyclists using infrared thermography

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

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 &#176;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.

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...

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.

The use of stationary bikes has increased significantly, making physical activity more accessible to the general population. However, the lack of precise, ...

We study muscle fatigue and biomechanics in amateur cyclists using infrared thermography. Current methods are not standardized. These protocols help detect fatigue using infrared thermography.To begin, line up the subjects who have consented to be a part of the study. Record the age and sex of each subject. Then, record the height and mass of the subject.Describe the Borg Rating of Perceived Exertion scale from six to 20 to the subjects. Instruct the subject to point to the number that represents their exertion level before and after the test. Prohibit the subject from consuming alcohol and nicotine for 24 hours prior to measurement.Instruct the subject to avoid caffeine intake and intense exercise for three hours before the test. Instruct the subject not to apply creams, cosmetics, or ointments to the lower extremities during the 12 hours prior to the test. After confirming the hydration status, record it on the pretest data sheet.Use a clinical scale to record the body mass before the test. Ask the subject to consume 300 milliliters of water 30 minutes before the session. Instruct the subject to fully undress the lower extremities and change into standardized black-like recycling shorts with no visible seams.Place a digital thermohygrometer one meter from the subject at a height of one meter. Record these values every five minutes in a spreadsheet. Ensure that there are no direct drafts, sunlight exposure, or heat or cold sources affecting thermoregulation.Perform a 15-minute seated rest period for acclimatization. Post-rest, position the subject on the stationary bicycle in the required posture. Use the infrared thermal camera with a minimum resolution of 320 by 240 pixels.Open the camera's Internal Settings menu. Navigate to object parameters, and set the emissivity to 0.98 for human skin. Set the reflected apparent temperature to match the previously measured ambient temperature.Use a laser distance meter or a measuring tape to position the tripod exactly 100 centimeters from the lateral plane of the bicycle crank set. Mark the tripod leg positions with adhesive tape. Enter the relative humidity and atmospheric temperature values into the instrument settings.Place the thermograph on a tripod and set the camera height to 30 centimeters above the floor. Position the lens at a perpendicular angle to the lower extremity of the subject. In the thermal analysis software, select the polygon or rectangle ROI tool.Click and drag to delineate a 10x5 centimeter box over the rectus femoris. Click Calculate to extract the mean temperature value. For setting the measurement point protocols, capture a thermographic image immediately after the 15-minute rest period.Before the end of the exercise period, stand behind the thermographic camera and preset the focus. Add the signal to stop pedaling. Extend the dominant leg to the 6 o'clock position.Press the capture or freeze button within five seconds. Capture a third thermographic image 10 minutes after exercise completion. Set the stationary bicycle to ergometer mode with a fixed workload of 150 watts.Use a metronome or console to maintain a cadence of 80 RPM. Instruct the subject to maintain this pace within a 5-RPM margin. Verify that the thermal camera is in standard recording mode with a temperature range of 20 to 45 degrees Celsius and a relative humidity between 40 and 55%Use the formula presented to calculate thermal shift.Preserve the original thermographic image while retaining full resolution and metadata for analysis. When compared with the resting phase, the immediate post-exercise moment showed redistribution of blood flow with a drop in surface temperature due to peripheral vasoconstriction and a rise in temperature in areas of pain, such as the knees. The recovery confirmed peripheral cooling, despite active heat retention in the central muscle bellies.This protocol can be applied in sports science, cycling research, and clinical studies of muscular fatigue and thermal regulation. This protocol allows researchers to measure muscle fatigue, thermal changes, and biomechanics during cycling. The most important challenge is controlling environmental conditions to ensure accurate and consistent thermal measurement.

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Research

JoVE Journal

Bioengineering

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Universidad Autónoma de Querétaro.  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.

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

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