Bicycle Set-Up Dimensions and Cycling Kinematics: A Consensus Statement Using Delphi Methodology.

Bicycle set-up dimensions and cycling kinematic data are important components of bicycle fitting and cyclist testing protocols. However, there are no guidelines on how bicycles should be measured and how kinematic data should be collected to increase the reliability of outcomes. This article proposes a consensus regarding bicycle set-up dimensions and recommendations for collecting cycling-related kinematic data. Four core members recruited panellists, prepared the document to review in each round for panellists, analysed the scores and comments of the expert panellists, reported the decisions and communicated with panellists. Fourteen experts with experience in research involving cycling kinematics and/or bicycle fitting agreed to participate as panellists. An initial list of 17 statements was proposed, rated using a five-point Likert scale and commented on by panellists in three rounds of anonymous surveys following a Delphi procedure. The consensus was agreed upon when more than 80% of the panellists scored the statement with values of 4 and 5 (moderately and strongly agree) with an interquartile range of less than or equal to 1. A consensus was achieved for eight statements addressing bicycle set-up dimensions (e.g. saddle height, saddle setback, etc.) and nine statements for cycling kinematic assessment (e.g. kinematic method, two-dimensional methodology, etc.). This consensus statement provides a list of recommendations about how bicycle set-up dimensions should be measured and the best practices for collecting cycling kinematic data. These recommendations should improve the transparency, reproducibility, standardisation and interpretation of bicycle measurements and cycling kinematic data for researchers, bicycle fitters and cycling related practitioners.

Effect of spinal cord injury on the skin temperature of different regions of interest during a graded exercise test in a moderate temperature environment.

The gradient between core and skin temperature is a relevant factor in heat exchange between the human body and the environment, but people with spinal cord injury (SCI), due to their autonomic dysfunction, have impaired mechanisms that condition skin temperature response. This study aimed to determine how SCI affects skin temperature response in different ROIs during a graded exercise test in a moderate temperature environment. 32 participants were included in the study [SCI (N = 16); Non-SCI (N = 16)]. A graded exercise test was conducted on an arm crank ergometer, with a staged duration of 3 min separated by 1 min of rest. Skin temperature was measured using infrared thermography at rest, after each interval and during recovery. Individuals with SCI exhibited lower skin temperature in the anterior leg during exercise than Non-SCI (p < 0.001). During recovery, SCI athletes experienced a lower skin temperature restoration in the anterior arm, posterior arm and anterior leg (p < 0.05). The anterior leg is an interesting region to measure during exercise in people with SCI for assessing the physiological effect of the injury, probably for the autonomic dysfunction in skin temperature regulation, but the effect observed during recovery in the arms suggests the presence of different mechanisms involved in skin temperature regulation.

Assessment of alternative metrics in the application of infrared thermography to detect muscle damage in sports.

Objective.The association between muscle damage and skin temperature is controversial. We hypothesize that including metrics that are more sensitive to individual responses by considering variability and regions representative of higher temperature could influence skin temperature outcomes. Here, the objective of the study was to determine whether using alternative metrics (TMAX, entropy, and pixelgraphy) leads to different results than mean, maximum, minimum, and standard deviation (SD) skin temperature when addressing muscle damage using infrared thermography.Approach.Thermal images from four previous investigations measuring skin temperature before and after muscle damage in the anterior thigh and the posterior lower leg were used. The TMAX, entropy, and pixelgraphy (percentage of pixels above 33 °C) metrics were applied.Main results.On 48 h after running a marathon or half-marathon, no differences were found in skin temperature when applying any metric. Mean, minimum, maximum, TMAX, and pixelgraphy were lower 48 h after than at basal condition following quadriceps muscle damage (p< 0.05). Maximum skin temperature and pixelgraphy were lower 48 h after than the basal condition following muscle damage to the triceps sural (p< 0.05). Overall, TMAX strongly correlated with mean (r= 0.85) and maximum temperatures (r= 0.99) and moderately with minimum (r= 0.66) and pixelgraphy parameter (r= 0.64). Entropy strongly correlates with SD (r= 0.94) and inversely moderately with minimum temperature (r= -0.53). The pixelgraphy moderately correlated with mean (r= 0.68), maximum (r= 0.62), minimum (r= 0.58), and TMAX (r= 0.64).Significance.Using alternative metrics does not change skin temperature outcomes following muscle damage of lower extremity muscle groups.

Dryfilm-ATR-FTIR analysis of urinary profiles as a point-of-care tool to evaluate aerobic exercise.

The understanding of metabolic alterations triggered by intense exercise can provide a biological basis for the development of new training and recovery methods. One popular way to monitor these changes is the non-invasive analysis of the composition of urine. This work evaluates the use of attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and multivariate analysis as a rapid and cost-effective way to investigate changes in urine composition after intense exercise. The urine FTIR spectra of 21 volunteers (14 going through aerobic exercise and 7 controls) were measured before and immediately, 2, 5, 11, and 24 h after running 10 km. Principal component analysis (PCA) and partial least squares analysis (PLS) regression were used to investigate the changes in the spectra as a function of the recovery time. PLS models obtained for the prediction of the time points in the exercise group were deemed significant (p < 0.05, rand t-test permutation testing in cross-validation), showing changes in the urine composition after the exercise, reaching a maximum after 11 hours as opposed to the control group which did not show any significant relationship with the recovery time. In a second step, spectra of the protean extract isolated from urines at significant timepoints (before, immediately after, and 11 hours after exercise) were measured. The PCA of the protein spectra showed clear differences in the spectra obtained at the separation between the recovery time points, especially after the end of the exercise, where the protein profile was significantly different from the other times. Results indicate that the technique was able to find differences in the urine after physical exertion and holds strong potential for an easy-to-use and simple screening metabolic evaluation of recovery methods.

Effect of different Volumes of exercise on skin temperature responses over the following 24 hours.

Skin temperature responses have been advocated to indicate exercise-induced muscle soreness and recovery status. While the evidence is contradictory, we hypothesize that the presence of muscle damage and the time window of measurement are confounding factors in the skin temperature response. The objective was to determine whether skin temperature is influenced by different workloads and the time course of temperature measurements over the following 24 h. 24 trained male military were assigned to one of three groups: GC group (n = 8) serving as control not performing exercises, GE group (n = 8) performing a simulated military combat protocol in an exercise track with different obstacles but designed not to elicit muscle damage, and the GEMD group (n = 8) performing the simulated military combat protocol plus 5 sets of 20 drop jumps, with 10-sec between repetitions and with 2-min of rest between sets aiming to induce muscle damage. Skin temperature was measured using infrared thermography before exercise (Pre) and 4 (Post4h), 8 (Post8h) and 24h (Post24h) post-exercise. Perception of pain (DOMS) was evaluated Pre, Post24h, and Post48h, and countermovement jump height was evaluated at Pre and Post24h. DOMS did not differ between groups in the Pre and Post24h measures but GEMD presented higher DOMS than the other groups at Post48h (p < 0.001 and large effect size). Jump height did not differ for GEMD and GC, and GE presented higher jump height at Post24h than GC (p = 0.02 and large effect size). Skin temperature responses of GEMD and GG were similar in all measurement moments (p > 0.22), and GE presented higher skin temperature than the GC and the GEMD groups at Post24h (p < 0.01 and large effect sizes). In conclusion, although physical exercise elicits higher skin temperature that lasts up to 24 h following the efforts, muscle soreness depresses this response.

Preliminary Application of Infrared Thermography to Monitoring of Skin Temperature Asymmetries in Professional Padel Players.

The aim of the present study was to evaluate skin temperature (Tsk) asymmetries, using infrared thermography, in professional padel players before (PRE), after (POST) and 10 min after training (POST10), and their relationship with perceptual variables and training characteristics. Thermal images were taken of 10 players before, after and 10 min after a standardized technical training. After training, Tsk of the dominant side was higher than before training in the anterior forearm (30.8 ± 0.4 °C vs. 29.1 ± 1.2 °C, p < 0.01; ES = 1.9), anterior shoulder (31.6 ± 0.6 °C vs. 30.9 ± 0.6 °C, p < 0.05; ES = 1.0) posterior arm (29.5 ± 1.0 °C vs. 28.3 ± 1.2 °C, p < 0.05; ES = 1.0), and posterior forearm (30.8 ± 0.9 °C vs. 29.3 ± 1.6 °C, p < 0.05; ES = 1.1). Likewise, these differences were significant POST10 in the anterior arm, anterior forearm, anterior shoulder, posterior arm and posterior forearm. Comparing the different moments of measurement (PRE, POST and POST10), the temperature was higher POST10 in all the regions analyzed except for the shoulder, abdominals, and lower back. Also, correlations were found between fatigue variation and temperature variation between limbs (Tsk dominance), and no correlation was found except between age and posterior thigh (|r| = 0.69; p < 0.05), and between the racket mass and anterior knee (|r| = 0.81; p < 0.01). In conclusion, infrared thermography allows monitoring of skin asymmetries between limbs in professional padel players, but these asymmetries were not related to overall fatigue variation, overall pain variation, years of experience and training hours.

Collaborative online international learning in physiology: a case study.

Internationalization in higher education is essential, and although active learning methodologies are increasing and allow students to develop transversal skills, most still have a very local scope. In this context, the Collaborative Online International Learning (COIL) methodology is an interesting approach to benefit the students' development. It consists of an online program that involves creating multicultural teams to develop a specific learning project. Although this methodology is expanding, its use in physiology is still scarce. This paper aims to show an example of applying COIL methodology in physiology topics to enhance higher-education students' innovation and business skills. Our example project developed a sports-assessment service concept focused on physiology and biomechanics assessments. The program involved teams from Brazil, Germany, and Spain, comprising undergraduate and master students. Over 7 weeks, these teams, mentored by professors and researchers, engaged in workshops covering COIL methodology, business model design, executive summary planning, economic analyses, and communication techniques. Key outcomes included learning new concepts, developing soft skills, building confidence in innovative solution proposals, and experiencing diverse cultures. Challenges faced were language barriers, scheduling, task complexity, and logistical issues. This experience confirms the effectiveness of incorporating programs using COIL methodology into educational curriculums. Doing so exposes physiology students to innovation, entrepreneurship, and business creation while strengthening their professional connections and opening up postgraduation opportunities.NEW & NOTEWORTHY Although the Collaborative Online International Learning (COIL) methodology is expanding, its use in physiology is still scarce. Our example COIL project of 7 weeks developed a sports-assessment service concept focused on physiology and biomechanics assessments. The program involved teams from Brazil, Germany, and Spain, comprising undergraduate and master's students. Students perceived extracurricular activities in this format as beneficial. Coaches also expressed positive views about such initiatives, noting benefits for students and their development.

A Preliminary Investigation about the Influence of WIMU PROTM Location on Heart Rate Accuracy: A Comparative Study in Cycle Ergometer.

Technological development has boosted the use of multi-sensor devices to monitor athletes' performance, but the location and connectivity between devices have been shown to affect data reliability. This preliminary study aimed to determine whether the placement of a multi-sensor device (WIMU PROTM) could affect the heart rate signal reception (GARMINTM chest strap) and, therefore, data accuracy. Thirty-two physical education students (20 men and 12 women) performed 20 min of exercise in a cycle ergometer based on the warm-up of the Function Threshold Power 20 test in laboratory conditions, carrying two WIMU PROTM devices (Back: inter-scapula; Bicycle: bicycle's handlebar-20 cm from the chest) and two GARMINTM chest straps. A one-dimensional statistical parametric mapping test found full agreement between the two situations (inter-scapula vs. bicycle's handlebar). Excellent intra-class correlation values were obtained during the warm-up (ICC = 0.99, [1.00-1.00], p < 0.001), the time trial test (ICC = 0.99, [1.00-1.00], p < 0.001) and the cool-down (ICC = 0.99, [1.00-1.00], p < 0.001). The Bland-Altman plots confirmed the total agreement with a bias value of 0.00 ± 0.1 bpm. The interscapular back placement of the WIMU PROTM device does not affect heart rate measurement accuracy with a GARMINTM chest strap during cycling exercise in laboratory conditions.

Acute effects of fatigue on internal and external load variables determining cyclists' power profile.

The aim of the present study was to determine whether fatigue affects internal and external load variables determining power profile in cyclists. Ten cyclists performed outdoor power profile tests (lasting 1-, 5 and 20-min) on two consecutive days, subject either to a fatigued condition or not. Fatigue was induced by undertaking an effort (10-min at 95% of average power output obtained in a 20-min effort followed by 1-min maximum effort) until the power output decreased by 20% compared to the 1-min power output. Fatigued condition decreased power output (p < 0.05, 1-min: 9.0 ± 3.8%; 5-min: 5.9 ± 2.5%; 20-min: 4.1 ± 1.9%) and cadence in all test durations, without differences in torque. Lactate decreased in longer efforts when a fatigue protocol had previously been conducted (e.g., 20-min: 8.6 ± 3.0 vs. 10.9 ± 2.7, p < 0.05). Regression models (r2 ≥ 0.95, p < 0.001) indicated that a lower variation in load variables of 20-min in fatigued condition compared with the non-fatigued state resulted in a lower decrease in critical power after the fatigue protocol. The results suggest that fatigued condition on power was more evident in shorter efforts and seemed to rely more on a decrease in cadence than on torque.

Can infrared thermography serve as an alternative to assess cumulative fatigue in women?

Muscle fatigue can limit performance both in sports and daily life activities. Consecutive days of exercise without a proper recovery time may elicit cumulative fatigue. Although it has been speculated that skin temperature could serve as an indirect indicator of exercise-induced adaptations, it is unclear if skin temperature measured by infrared thermography (IRT) could be an outcome related to the effects of cumulative fatigue. In this study, we recruited 21 untrained women and induced cumulative fatigue in biceps brachii over two consecutive days of exercise. We measured delayed onset muscle soreness (DOMS, using a numeric rate scale), maximal strength (using a dynamometer), and skin temperature (using IRT) in exercise and non-exercise muscles. Cumulative fatigue reduced muscle strength and increased DOMS. Skin temperature in the arm submitted to cumulative fatigue was higher for minimum and mean temperature, being asymmetrical in relation to the control arm. We also observed that the variations in the minimum and mean temperatures correlated with the strength losses. In summary, skin temperature measured by IRT seems promising to help detect cumulative fatigue in untrained women, being useful to explain strength losses. Future studies should provide additional evidence for the potential applications not only in trained participants but also in patients that may not be able to report outcomes of scales or precisely report DOMS.

Acute physiological responses to a pyramidal exercise protocol and the associations with skin temperature variation in different body areas.

This study aimed to examine the skin temperature (Tsk) variations in five regions of interest (ROI) to assess whether possible disparities between the ROI's Tsk could be associated with specific acute physiological responses during cycling. Seventeen participants performed a pyramidal load protocol on a cycling ergometer. We synchronously measured Tsk in five ROI with three infrared cameras. We assessed internal load, sweat rate, and core temperature. Reported perceived exertion and calves' Tsk showed the highest correlation (r = -0.588; p < 0.01). Mixed regression models revealed that the heart rate and reported perceived exertion were inversely related to calves' Tsk. The exercise duration was directly associated with the nose tip and calf Tsk but inversely related to the forehead and forearm Tsk. The sweat rate was directly related to forehead and forearm Tsk. The association of Tsk with thermoregulatory or exercise load parameters depends on the ROI. The parallel observation of the face and calf Tsk could indicate simultaneously the observation of acute thermoregulatory needs and individual internal load. The separate Tsk analyses of individual ROI appear more suitable to examine specific physiological response than a mean Tsk of several ROI during cycling.

Clinical results of lumbar sympathetic blocks in lower limb complex regional pain syndrome using infrared thermography as a support tool.

AIM: To describe the clinical outcomes for a group of complex regional pain syndrome patients using infrared thermography as an intraprocedural support tool when undertaking fluoroscopy-guided lumbar sympathetic blocks. SUBJECTS: 27 patients with lower limb complex regional pain syndrome accompanied by severe pain and persistent functional impairment. METHODS: A series of three fluoroscopic-guided lumbar sympathetic blocks with local anesthetic and corticoids using infrared thermography as an intraprocedural support tool were performed. Clinical variables were collected at baseline, prior to each block, and one, three, and six months after blocks in a standardized checklist assessing each of the clinical categories of complex regional pain syndrome stipulated in the Budapest criteria. RESULTS: 23.75% of the blocks required more than one chance to achieve the desired thermal pattern and therefore to be considered as successful. A decrease in pain measured on a visual analogic scale was observed at all time points compared to pre-blockade data, but only 37% of the cases were categorized as responders, representing a ≥ 30% decrease in VAS, with the disappearance of pain at rest. An improvement of most of the clinical variables recorded was observed, such as tingling, edema, perception of thermal asymmetry, difference in coloring and sweating. There was a significant decrease of neuropathic pain and improvement of functional limitation. Logistic regression analysis showed the main variable to explain the probability of being a responder was immobilization time (odds ratio of 0.89). CONCLUSION: A series of fluoroscopy-guided lumbar sympathetic blocks controlled by infrared thermography in the treatment of lower limb CRPS showed a responder rate of 37%.

Application of machine learning algorithms in thermal images for an automatic classification of lumbar sympathetic blocks.

PURPOSE: There are no previous studies developing machine learning algorithms in the classification of lumbar sympathetic blocks (LSBs) performance using infrared thermography data. The objective was to assess the performance of different machine learning algorithms to classify LSBs carried out in patients diagnosed with lower limbs Complex Regional Pain Syndrome as successful or failed based on the evaluation of thermal predictors. METHODS: 66 LSBs previously performed and classified by the medical team were evaluated in 24 patients. 11 regions of interest on each plantar foot were selected within the thermal images acquired in the clinical setting. From every region of interest, different thermal predictors were extracted and analysed in three different moments (minutes 4, 5, and 6) along with the baseline time (just after the injection of a local anaesthetic around the sympathetic ganglia). Among them, the thermal variation of the ipsilateral foot and the thermal asymmetry variation between feet at each minute assessed and the starting time for each region of interest, were fed into 4 different machine learning classifiers: an Artificial Neuronal Network, K-Nearest Neighbours, Random Forest, and a Support Vector Machine. RESULTS: All classifiers presented an accuracy and specificity higher than 70%, sensitivity higher than 67%, and AUC higher than 0.73, and the Artificial Neuronal Network classifier performed the best with a maximum accuracy of 88%, sensitivity of 100%, specificity of 84% and AUC of 0.92, using 3 predictors. CONCLUSION: These results suggest thermal data retrieved from plantar feet combined with a machine learning-based methodology can be an effective tool to automatically classify LSBs performance.

Does Nordic Walking technique influence the ground reaction forces?

BACKGROUND: Nordic Walking (NW) practice has increased during the last decade, generating great benefits related to the reduction of ground reaction forces (GRF). However, there is still limited evidence regarding how the NW technique could affect GRF. RESEARCH QUESTION: To analyze the effect of the speed and the differences in ground reaction forces (GRF) between NW with Diagonal technique (DT) versus Alpha technique (AT) and compare them with normal walking (W) METHODS: 29 male physically active sport science students were randomly assigned to one of the training groups: AT (n = 15) or DT (n = 14). After 5 technique familiarization sessions, participants performed 5 experimental trials on a walkway for both NW and W at two different walking speeds, previously randomized. A two-way repeated measures ANOVA analysis was carried out to find differences between speeds (preferred, fast) and gait (NW, W) as within-subject factors and NW techniques (DT vs AT) as between-subject factor. RESULTS: During NW, both technique groups (AT, DT) showed an increase in GRF variables compared to W, such as in stance time (2.9 % mean increment, p < 0.01, ES = 0.3; 95 %IC[-0.027, -0.008]), vertical force impact or vertical heel strike variables (4.9 % mean increment, p < 0.01, ES = 0.4; 95 %IC[0.101, 0.036]; 7.3 % mean increment, p < 0.01, ES = 0.8; 95 %IC[-0.133, -0.081] respectively). Moreover, AT group experienced significant lower forces at vertical force at midstance (10.1 % mean descent, p = 0.036, ES = 0.3; 95 %IC[-0.083, -0.009]) and higher forces at AP propulsive forces (23.7 % mean increment, p < 0.001, ES = 0.6; 95 %IC[0.078, 0.202) and ML max force (14.0 % mean increment, p = 0.045, ES = 0.3; 95 %IC[0.002, 0.026]) compared to DT group. Walking speed was significantly higher during NW (Preferred: 1.89 ± 0.18 m/s; Fast: 2.17 ± 0.21 m/s) compared to W (Preferred: 1.76 ± 0.15 m/s; Fast: 2.04 ± 0.19 m/s) in both speed conditions. SIGNIFICANCE: NW favours an increase in GRF and speed in comparison with Walking, independently of the technique, with no evidence that justifies the use of one technique or another.

Duration Effects on Wingate and Functional Power Threshold Test Outputs in Female Cyclists.

The response of female cyclists depending on the functional test duration has not been studied. This study aims to analyse the effect of modification of the duration of two different functional tests: Wingate (WAnT) and Functional Power Threshold (FTP) in female cyclists. Fourteen cyclists (27±8 years, 1,66±0,08 m, and 60,6±7,2 kg) performed 2 test days with a 24-hour break between days, varying the test duration (WAnT 20- or 30-sec, and FTP 8- or 10-min). Relative power output, cadence, heart rate, local oxygen saturation, lactate, and rating of perceived exertion were measured in each test. Time duration did not affect the power output outcomes in both tests (p>0,05). However, WAnT of 20 sec, compared with the test of 30 sec, resulted in a lower cadence decrease in the last 5 sec (p<0,01, ES=1,3), lower heart rate variables (peak, average and variation; p<0,01, ES>0,5), and higher execution inclination of local oxygen saturation (p<0,05 and ES=1,0). In conclusion, the time variations assessed do not alters power outcomes in female cyclists. However, higher acute fatigue can be observed in the WAnT of 30 sec, which suggests the use of the test of 20 sec to allow continue training afterwards.

Reproducibility of skin temperature analyses by novice and experienced evaluators using infrared thermography.

Infrared thermography (IRT) has become popular in several areas of knowledge. However, the analyses of thermal images often request manual actions, and little is known about the effect of the evaluator's experience on analysis thermal images. Here, we determine the reproducibility of IRT images analysis performed by evaluators with different levels of experience. Eight evaluators (GE, group experienced, n = 4; GN, group novice, n = 4) analyzed thermograms from 40 healthy participants recorded before and after exercise to determine the mean, minimum, maximum, standard deviation, and range of skin temperature in the anterior thigh and posterior leg. Before and after exercise, mean temperature showed excellent reproducibility for both groups for the anterior thigh (ICC >0.98) and posterior leg (ICC >0.94), and maximum temperature showed excellent reproducibility for both groups in the posterior leg (ICC >0.91). The influence of experience level was not significant considering the anterior thigh. Similarly, experience level did not affect the mean, maximum, and standard deviation temperature determined for the posterior leg. For the posterior leg, minimum temperature presented lower values and the range was higher among novice evaluators. Mean skin temperature showed narrower 95% limits of agreement than minimum and maximum for both regions and moments. Caution is advised when temperature ranges and minimums are determined by different evaluators. We conclude that for IRT analysis by evaluators with different levels of experience, the mean and maximum temperatures should be prioritized due to their better reproducibility.

Chronic and Acute Effects on Skin Temperature from a Sport Consisting of Repetitive Impacts from Hitting a Ball with the Hands.

Valencian handball consists in hitting the ball with the hands and it may contribute to injury development on the hands. This study aimed to analyze skin temperature asymmetries and recovery after a cold stress test (CST) in professional players of Valencian handball before and after a competition. Thirteen professional athletes and a control group of ten physically active participants were measured. For both groups, infrared images were taken at the baseline condition; later they underwent a thermal stress test (pressing for 2 min with the palm of the hand on a metal plate) and then recovery images were taken. In athletes, the images were also taken after their competition. Athletes at baseline condition presented lower temperatures (p < 0.05) in the dominant hand compared with the non-dominant hand. There were asymmetries in all regions after their match (p < 0.05). After CST, a higher recovery rate was found after the game. The regions with the most significant differences in variation, asymmetries and recovery patterns were the index, middle and ring fingers, and the palm of the dominant hand. Taking into account that lower temperatures and the absence of temperature variation may be the consequence of a vascular adaptation, thermography could be used as a method to prevent injuries in athletes from Valencian handball.

New Advances in Human Thermophysiology.

Human thermoregulation is the integrative physiological responses of the body used to maintain a core temperature with values close to 37 °C, even in a wide range of activities and environments [...].

Effects of different hydration supports on stride kinematics, comfort, and impact accelerations during running.

BACKGROUND: Different supports for hydration can influence total body mass and affect running biomechanics. RESEARCH QUESTION: Do different hydration supports affect the perceived exertion and comfort, stride kinematics, and impact accelerations during running? METHODS: This was a crossover study design. Thirteen trail runners completed a treadmill running test divided into four different durations and randomized hydration supports conditions, lasting 8 min each at moderate intensity: A) waist bag (0.84 kg); B) medium load backpack (0.84 kg); C) full load backpack (3.40 kg); and D) a control condition without water support. Impact accelerations were measured for 30 s in 4, 6, and 8 min. The rate of perceived exertion and heart rate were registered on minutes 4 and 8. At the last minute of each condition, comfort perception was registered RESULTS AND SIGNIFICANCE: No condition affected the stride kinematics. Full load backpack condition reduced head acceleration peak (-0.21 g; p = 0.04; ES=0.4) and head acceleration magnitude (-0.23 g; p = 0.03; ES=0.4), and increased shock attenuation (3.08 g; p = 0.04; ES=0.3). It also elicited higher perceived exertion (p < 0.05; ES>0.8) being considered heavier (p < 0.01; ES > 1.1). The waist bag condition was more comfortable in terms of noise (p = 0.006; ES=1.3) and humidity/heat (p = 0.001; ES=0.8). The waist bag was the most comfortable support. On the other hand, the full backpack elicited lower comfort and was the only generating compensatory adjustments. These results may help to improve design of full load backpack aiming at comfort for runners.