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.

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.

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.

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.

Consistency of pacing profile according to performance level in three different editions of the Chicago, London, and Tokyo marathons.

Running pacing has become a focus of interest over recent years due to its relationship with performance, however, it is still unknown the consistency of each race in different editions. The aim of this study is to analyze the consistency of pacing profile in three consecutive editions of three marathon races. A database of 282,808 runners, compiled from three different races (Chicago, London, and Tokyo Marathon) and three editions (2017, 2018, and 2019) was analyzed. Participants were categorized according to their time performance in the marathon, every 30 min from 2:30 h to sub-6 h. The relative speed of each section for each runner was calculated as a percentage of the average speed for the entire race. The intraclass correlation coefficients (ICC) of relative speed at the different pacing section, taking into account the runner time categories, was excellent over the three marathon editions (ICC > 0.93). The artificial intelligence model showed an accuracy of 86.8% to classify the runners' data in three marathons, suggesting a consistency between editions with identifiable differences between races. In conclusion, although some differences have been observed between editions in certain sections and marathon runner categories, excellent consistency of the pacing profile was observed. The study of pacing profile in a specific marathon can, therefore, be helpful for runners, coaches and marathon organizers for planning the race and improving its organization.

Higher Hamstrings Strength and Stability Are Related to Lower Kinematics Alteration during Running after Central and Peripheral Fatigue.

Fatigue can be classified as peripheral or central depending on the extent of its effects. Muscle strength reduction, associated with the appearance of fatigue during running, produces kinetics and kinematics modifications which could lead to an increased risk of injury. This study aimed to analyze the effect of peripheral and central fatigue protocols in running kinematics and to investigate the relationship between isokinetic strength and dynamic stability in fatigue related changes. Eighteen male recreational runners participated in the study. The dynamic postural stability index (DPSI) and quadriceps and hamstring isokinetic strength were assessed before the fatigue test. Then, angular kinematics during treadmill running were evaluated in pre- and post-fatigue states (central and peripheral). The results showed that runners with higher hamstring isokinetic strength and better DPSI had lower modifications after central fatigue of stance time, knee flexion, vertical and leg stiffness, and ankle dorsiflexion during the absorption and propulsion phases (r > 0.400, p < 0.05). Moreover, small changes in ankle dorsiflexion at initial contact after peripheral fatigue are related to a better DPSI and higher hamstring isokinetic strength (r > 0.400, p < 0.05). In summary, high values of hamstring isokinetic concentric strength and dynamic stability are related to lower increases of range of movements during running after central and peripheral fatigue. So, fatigue may affect to a lesser extent the running technique of those runners with higher hamstring strength and stability values.

Plantar pressure distribution during running with a self-customized foot orthosis in a home microwave.

The individualization of a custom-made foot orthosis could provide improvements in plantar loading distribution regarding a prefabricated one. However, not all runners can afford it because of its high cost. A new type of low-cost prefabricated foot orthoses with self-customization could be the solution. The aim of the study was to evaluate if self-customized prefabricated foot orthoses (SCFO) could improve plantar pressure distribution with respect to generic prefabricated ones without customization, during the intense prolonged running. Thirty healthy recreational runners performed two tests of 30 min running on a treadmill, each one with a foot orthosis condition, on different days. Mean peak pressure, pressure-time integral, relative pressure and stance time were measured at the beginning and at the end of the tests. Plantar pressure data were analyzed in nine foot regions. Two-way repeated-measures ANOVAs were performed. SCFO reduced relative pressure in metatarsals (P < 0.005) and lateral heel (P = 0.004), thanks to a greater involvement of arch area in mean peak pressure (medial: P = 0.006 and lateral: P = 0.019) and relative pressure (P < 0.001). In general, prolonged run increased pressures in forefoot, in both foot orthosis, but with lower values in metatarsals with SCFO (P < 0.022), which also helped reduce relative pressure in midfoot (P = 0.007) and medial heel (P = 0.035). Stance time was not modified in any case (P > 0.05). In conclusion, customization and better fit of a low-cost prefabricated foot orthosis can improve plantar pressure distribution during a prolonged run, being a good prevention mechanism for plantar overloading in healthy runners.

Acute Effects on Impact Accelerations Running with Objects in the Hand.

Amateur runners usually run carrying implements in their hands (keys, a mobile phone, or a bottle of water). However, there is a lack of literature about the effects of different handloads on impact accelerations. Thus, this study aimed to analyse the effects of carrying different objects in the hand on impact accelerations during running. Nineteen male recreational runners (age 24.3 ± 6.8 years, training volume of 25 ± 7.38 km/week) performed twenty minutes of running on a treadmill at 2.78 m/s with four different conditions: no extra weight, with keys, with a mobile phone, and with a bottle of water. Impact acceleration and spatio-temporal parameters were analysed through a wireless triaxial accelerometry system composed of three accelerometers: two placed in each tibia and one placed on the forehead. A higher tibia acceleration rate in the dominant leg was observed when participants ran holding both a mobile phone (p = 0.027; ES = 0.359) and a bottle of water (p = 0.027; ES = 0.359), compared to no extra weight. No changes were observed in peak acceleration, acceleration magnitude, and shock attenuation in any other conditions. Likewise, neither stride frequency nor step length was modified. Our results suggest that recreational runners should not worry about carrying objects in their hands, like a mobile phone or a bottle of water, in short races because their effect seems minimal.

Impact accelerations during a prolonged run using a microwavable self-customised foot orthosis.

The use of custom-made foot orthoses has been associated with numerous benefits, such as decreased impact accelerations. However, it is not known whether this effect could be due to better customisation. The present study analysed the effects of the first generation of  a microwavable prefabricated self-customised foot orthosis vs. a prefabricated standard one on impact accelerations throughout a prolonged run. Thirty runners performed two tests of 30-min running on a treadmill, each one with an orthosis condition. Impact acceleration variables of tibia and head were recorded every 5 min. Microwavable self-customised foot orthosis increased the following variables in the first instants compared to the prefabricated standard one: tibial peak (min1: 6.5 (1.8) vs. 6.0 (1.7) g, P = .009, min5: 6.6 (1.7) vs. 6.2 (1.7) g, P = .035), tibial magnitude (min1: 8.3 (2.6) vs. 7.7 (2.4) g, P = .030, min5: 8.5 (2.6) vs. 7.9 (2.5) g, P = .026) and shock attenuation (min1: 61.4 (16.8) vs. 56.3 (16.3)%, P = .014, min5: 62.0 (15.5) vs. 57.2 (15.3)%, P = .040), and tibial rate throughout the entire run (504.3 (229.7) vs. 422.7 (212.9) g/s, P = .006). However, it was more stable throughout 30-min running (P < .05). These results show that the shape customisation entailed by the thermoformable material does not provide impact acceleration improvements.

Footwear outsole temperature may be more related to plantar pressure during a prolonged run than foot temperature.

Objective. The temperature of the sole of the foot has been suggested as an alternative to the measurement of plantar pressure during running despite the scarce evidence about their relationship. The temperature of the footwear outsole could also be representative of plantar pressure distribution due to its less multifactorial dependence. The aim of the study was to determine if plantar pressure during a prolonged run could be related to plantar temperature, either of the sole of the foot or the footwear outsole.Approach. Thirty recreational runners (15 males and 15 females) performed a 30 min running test on a treadmill. Thermographic images of the sole of the foot and the footwear outsole were taken before and immediately after the test, and dynamic plantar pressure was measured at the end of the test. Pearson correlations and stepwise multiple linear regressions were performed.Main results.Plantar pressure percentage was related to a moderate correlation with plantar temperature percentage in forefoot and rearfoot (P < 0.05), showing a greater relationship with the footwear outsole than with the sole of the foot (r = 0.52-0.73 versusr = 0.40-0.61, respectively). Moreover, moderate correlations were also observed between footwear outsole and sole of the foot temperature variables, especially in rearfoot.Significance. Footwear outsole temperature may be better related to plantar pressure distribution than sole of the foot temperature, in the forefoot and rearfoot. The midfoot is the most sensitive and variable region to analyze, as it does not seem to have any relationship with plantar pressure.

Influence of infrared camera model and evaluator reproducibility in the assessment of skin temperature responses to physical exercise.

Infrared thermography (IRT) has been gaining in popularity in clinical and scientific research due to the increasing availability of affordable infrared cameras. This study aims to determine the similarity of measurement performance between three models of IRT camera during assessment of skin temperature before and after physical exercise. Three models of FLIR thermographic cameras (E60bx, Flir-One Pro LT, and C2) were tested. Thermal images were taken of the foot sole, anterior leg, and anterior thigh from 12 well-trained men, before and after a 30-min run on a treadmill. Image files were blinded and processed by three evaluators to extract the mean, maximum, and standard deviation of skin temperature of the region of interest. Time for data processing and rate of perceived effort was also recorded. Data processing was slower on the E60bx (CI95% E60 vs C2 [0.2, 2.6 min], p = 0.02 and ES = 0.6); vs. Flir-One [0.0, 3.4 min], p = 0.03 and ES = 0.6) and was associated with lower effort perception (E60 3.0 ± 0.1 vs. Flir-One 5.6 ± 0.2 vs C2 7.0 ± 0.2 points; p < 0.001 and ES > 0.8). The C2 and Flir-One cameras underestimated the temperature compared with the E60. In general, measuring mean temperature provided higher camera and examiner intra-class correlations than maximum and standard deviation, especially before exercise. Moreover, post exercise mean skin temperatures provided the most consistent values across cameras and evaluators. We recommend the use of mean temperature and caution when using more than one camera model in a study.

Pre-exercise skin temperature evolution is not related with 100 m front crawl performance.

During the transition between warm-up and competition there is a change in core, muscle and (eventually) skin temperature that may affect swimming performance. We have aimed to assess skin temperature evolution during transition phases of different durations before a typical front crawl effort and to investigate its relationship with performance. Following a standardized warm-up, nine adolescent male swimmers performed three maximal randomized 100 m maximum front crawl trials after 10, 20 and 45 min transition phases. Skin temperature, performance (time, stroke frequency, length and index, and propelling efficiency), heart rate, lactate and perceived effort were assessed. Data showed a skin temperature log increase over time (R2 > 0.96, p < 0.01) without differences from the 15 min with the following instants. Performance and psychophysiological variables were similar between transition phases. However, skin temperature at the end of the transition periods, i.e., just before the 100 m trials, was lower in the 10 min than the 20 and 45 min transitions (32.0 ± 0.6 vs 33.0 ± 0.4 and 33.5 ± 0.5 °C, respectively). The main finding was that no relevant relationships were observed between pre-test skin temperature and performance times (|r| < 0.6, p > 0.05) for the studied transition phases. We have concluded that transitions longer than 10 min will not present thermal changes and that, within the physiologic limits studied, pre-exercise skin temperature does not influence swimming performance.

Validation of ThermoHuman automatic thermographic software for assessing foot temperature before and after running.

The aim of the study was to evaluate an automatic thermographic software package (ThermoHuman®) for assessing skin temperature on the soles of the feet before and after running and to compare it with two manual definitions of the regions of interest (ROIs). 120 thermal images of the soles of the feet of 30 participants, at two measurement points (before and after running 30 min) and on two measurement days were analyzed. Three different models of thermographic image analyses were used to obtain the mean temperature of 9 ROIs: A) ThermoHuman (automatic definition of ROIs using ThermoHuman® software), B) Manual (manual delimitation of ROIs by proportion criteria), and C) Manual-TH (manual delimitation of ROIs in an attempt to replicate the regions analyzed by ThermoHuman). ThermoHuman resulted in an 86% reduction in time involved compared to manual delimitation. Fourteen of the 120 images (12%) presented some error in one or more of the ROI delimitations. Although the three procedures presented significant differences between them (53% in the comparison between ThermoHuman and Manual, 47% between ThermoHuman and Manual-TH, and 28% between Manual and Manual-TH), all differences had a small effect size (ES 0.2-0.4) or lower (ES < 0.2). Bland-Altman plots showed similar 95% limits of agreement between the three procedures before and after running. Intraclass correlation coefficient analysis of the three procedures presented excellent reliability (ICC>0.8). In conclusion, ThermoHuman® software was observed to be time-saving for image analysis with excellent reliability. Although results suggest that ThermoHuman® and manual methods are both valid in themselves, combining them is not recommended due to the differences observed between them.

Effect of prefabricated thermoformable foot orthoses on plantar surface temperature after running: A gender comparison.

There is a lack of evidence about the effect of different type of foot orthoses on plantar surface temperature. Moreover, that effect could be different depending on gender due to anatomical and physiological differences between men and women. The aim of the study was to analyze the effect of a prefabricated thermoformable foot orthosis on plantar surface temperature after running and taking gender differences into account. Thirty recreational runners (15 males, mean (standard deviation): 28 (7) years, 69.7 (6.5) kg, 1.74 (0.05) cm and 22.9 (1.7) kg/m2; and 15 females: 35 (7) years, 55.2 (6.9) kg, 1.63 (0.06) cm and 20.6 (1.9) kg/m2) carried out a maximum incremental test as pre-test, and two running tests on a treadmill at the laboratory wearing previously randomized different foot orthoses (thermoformable and prefabricated generic). The plantar surface temperature of the dominant foot sole in ten regions of interest was assessed before and immediately after 30-min running at 75% of VO2max. The use of thermoformable foot orthoses produced lower temperatures only in men after the run in medial heel (P = 0.033, ES = 0.7), which then disappeared in temperature variation (after - before) (P = 0.910). Regarding gender, women showed lower temperatures before the run in both orthosis conditions (P < 0.039, ES > 0.8), but no differences in temperatures after the run (P = 0.910) in comparison with men. Moreover, absolute temperatures after running were always greater than before the run (P < 0.001, ES > 5.0). In conclusion, the thermoformable foot orthoses do not modify plantar surface temperature after running in healthy runners of either gender, compared to prefabricated generic foot orthoses. Although women present lower baseline plantar temperatures than men, these differences disappear after exercise.

Effect of custom-made and prefabricated foot orthoses on kinematic parameters during an intense prolonged run.

Foot orthoses are one of the most used strategies by healthy runners in injury prevention and performance improvement. However, their effect on running kinematics throughout an intense prolonged run in this population is unknown. Moreover, there is some controversy regarding the use of custom-made versus prefabricated foot orthoses. This study analysed the effect of different foot orthoses (custom-made, prefabricated and a control condition) on spatio-temporal and angular (knee flexion and foot eversion) kinematic parameters and their behaviour during an intense prolonged run. Twenty-four recreational runners performed three similar tests that consisted of running 20 min on a treadmill at 80% of their maximal aerobic speed, each one with a different foot orthosis condition. Contact and flight time, and stride length and stride rate were measured every 5 min by an optical measurement photoelectric cell system. Knee flexion and foot eversion kinematic parameters were measured by two high-speed cameras. No significant differences were found between the different foot orthoses in any of the time points studied and between the interaction of foot orthosis and behaviour over time, in any of the variables studied (P > 0.05). The use of custom-made and prefabricated foot orthoses during an intense prolonged run does not produce changes in spatio-temporal and kinematic parameters in healthy runners. These results suggest that a healthy runner maintains its ideal movement pattern throughout a 20 minute prolonged run, regardless the type of foot orthosis used.

Relationship between foot eversion and thermographic foot skin temperature after running.

The main instruments to assess foot eversion have some limitations (especially for field applications), and therefore it is necessary to explore new methods. The objective was to determine the relationship between foot eversion and skin temperature asymmetry of the foot sole (difference between medial and lateral side), using infrared thermography. Twenty-two runners performed a running test lasting 30 min. Skin temperature of the feet soles was measured by infrared thermography before and after running. Foot eversion during running was measured by kinematic analysis. Immediately after running, weak negative correlations were observed between thermal symmetry of the rearfoot and eversion at contact time, and between thermal symmetry of the entire plantar surface of the foot and maximum eversion during stance phase (r=-0.3 and p=0.04 in both cases). Regarding temperature variations, weak correlations were also observed (r=0.4 and p<0.05). The weak correlations observed in this study suggest that skin temperature is not related to foot eversion. However, these results open interesting future lines of research.

Initiating running barefoot: Effects on muscle activation and impact accelerations in habitually rearfoot shod runners.

Runners tend to shift from a rearfoot to a forefoot strike pattern when running barefoot. However, it is unclear how the first attempts at running barefoot affect habitually rearfoot shod runners. Due to the inconsistency of their recently adopted barefoot technique, a number of new barefoot-related running injuries are emerging among novice barefoot runners. The aim of this study was therefore to analyse the influence of three running conditions (natural barefoot [BF], barefoot with a forced rearfoot strike [BRS], and shod [SH]) on muscle activity and impact accelerations in habitually rearfoot shod runners. Twenty-two participants ran at 60% of their maximal aerobic speed while foot strike, tibial and head impact accelerations, and tibialis anterior (TA), peroneus longus (PL), gastrocnemius medialis (GM) and gastrocnemius lateralis (GL) muscle activity were registered. Only 68% of the runners adopted a non-rearfoot strike pattern during BF. Running BF led to a reduction of TA activity as well as to an increase of GL and GM activity compared to BRS and SH. Furthermore, BRS increased tibial peak acceleration, tibial magnitude and tibial acceleration rate compared to SH and BF. In conclusion, 32% of our runners showed a rearfoot strike pattern at the first attempts at running barefoot, which corresponds to a running style (BRS) that led to increased muscle activation and impact accelerations and thereby to a potentially higher risk of injury compared to running shod.