Exercise induces modifications in thermal homeostasis. The type of exercise may have a specific impact on skin temperature (Tsk).
ObjectiveTo analyze and compare the behavior of Tsk in a resistance training between men and women and monitor the thermal recovery response.
Material and MethodsSixteen male and female adults (24.56±3.22 years old) underwent a resistance circuit training session. They performed 3 sets of 12 repetitions with 70–80% 1 RM for lat pulldown, leg press, and biceps arm curl exercises. Thermograms were taken in anterior and posterior body view at rest, 20min, and 24h after training. Tsk was measured in the body regions of interest corresponding to the brachial biceps, quadriceps, and upper back. ANOVA with Tukey's post hoc test was used to analyze Tsk changes among moments, and independent samples t-test was used to compare Tsk between males and females.
ResultsAt rest, women showed Tsk significantly lower than men. There was no significant Tsk change 20min after exercise. However, Tsk increased 24h after exercise in the upper back for men compared with baseline and in quadriceps for women compared with baseline and 20min after exercise (p<0.05).
ConclusionThe Tsk of women at rest is lower than that of men. A resistance circuit training session does not significantly change Tsk 20min after exercise, but it increases Tsk 24h after training in the upper back for men and quadriceps for women.
Physical exercise changes the body's thermal response.1,2 It is interesting to understand how the different types of exercise impact thermal adjustments to find alternatives that facilitate the control of body temperature. Infrared thermography (IRT) records the heat radiated by a body, allowing us to understand the thermoregulatory adjustments during exercise.3 IRT has been used to study thermoregulatory responses mainly related to aerobic and cyclical exercises.4–8 However, in the case of strength exercises and especially with women, the density of studies on the subject is unusual.
In a search carried out in April 2020 in the PubMed database using the keywords “thermography and exercise”, with the filter “humans”, it was possible to find 134 articles, with only five studies on IRT and strength training.9–13 Among these studies, only one was conducted with women.12 Another interesting aspect is that in the methodology used by these five articles,9–13 none of them was carried out with full training sessions. The authors used protocols with only one exercise to verify the skin temperature (Tsk) response during, just after, or in the recovery period, making it necessary to evaluate the Tsk response resulting from a complete circuit-based strength exercise session. Moreover, it was possible to observe that most of the studies used men as volunteers, probably for methodological reasons.
In this work, it has been proposed to analyze the thermal response 24h after exercise as a possible tool to control the training load.14 IRT could help to understand the local thermal behavior induced by the effect of exercise on cellular regenerative responses through inflammatory and local anabolic responses, such as the recovery of muscle glycogen and the phosphate system.15 Some studies have found an interesting relationship using this approach with soccer players,14,16 who showed that the active body regions were warmer 24h after exercise compared to the resting conditions. This would mean that this body region would still be in the recovery phase, requiring to return at rest Tsk values for performing a new training load.
Since strength training is one of the most important means to improve physical fitness, it is important to know how this process occurs because it differs from the type of aerobic exercise due to its bioenergetic specificities. This study aims to increase the basic scientific knowledge, thus expanding the level of scientific evidence on thermoregulatory adaptations of strength training, especially with a subgroup of women. Therefore, the objective of this study was to analyze and compare the behavior of Tsk between men and women after a session of circuit-based resistance exercise, as well as to analyze the effect of this type of exercise after a 24-h recovery period.
Materials and methodsParticipantsSixteen physically active adults participated in this study (8 males and 8 females) (18–30 years old). All were enrolled in strength training in the last 2 months and were classified as apparently healthy subjects, with negative responses to all PAR-Q questions,17 and classified as having a below-average coronary risk.18 Throughout the data collection protocol, the Brazilian ethical standards for research with human beings were followed according to Law 466/12, which is in line with procedures and methods used for the ethical standards of experiments with humans proposed by the Declaration of Helsinki.19
The following exclusion criteria were considered: smoking subjects, musculoskeletal injuries in the last two months, skin burns (in the analyzed body regions), pain symptoms in the evaluated areas, skin allergies, sleep disorders, fever in the last seven days, medical or physical therapy with creams, ointments or lotions, as well as the use of antipyretics and/or diuretics, any nutritional supplement that could change the water body homeostasis or body temperature in the last two weeks, or eating disorders (bulimia and anorexia).20Table 1 shows the anthropometric characteristics of the participants.
Anthropometric characteristics of male and female participants. M=male; F=female.
Gender | N | Age (years old) | Height (m) | Body mass (kg) | Body fat (%)* |
---|---|---|---|---|---|
F | 8 | 24.5±3.38 (20–30) | 1.64±0.04 (1.58–1.69) | 59.18±4.37 (53–66) | 15.32±3.26 (11.8–19.7) |
M | 8 | 24.6±3.29 (21–30) | 1.77±0.02 (1.73–1.82) | 77.7±3.02 (73.2–83) | 11.98±5.94 (4–19.2) |
Proposed by Jackson and Pollock.21 three skinfolds (chest, abdomen, and thigh for men, and triceps, suprailium, and thigh for women).
Fig. 1 shows the four phases in which the study was developed.
In PHASE 1, an anthropometric assessment was performed to characterize the participants. Moreover, the 1RM test was carried out following the recommendations proposed by Marins and Giannichi,22 in three exercises: dumbbell biceps arm curl, lat pulldown, and leg press. First, a 10-min organic warm-up was performed on a cycle ergometer. Subsequently, participants were familiarized with the strength exercises. Finally, participants underwent the 1RM test; they were asked to perform one repetition with adequate technique throughout the range of motion, in the cadency 2:2 (2s in the concentric phase and 2s in the eccentric phase) until reaching the maximum load.23
At least 48h after the 1RM test, participants came back to the lab for the load calibration test (PHASE 2). On this day, the warm-up period included an organic phase on a cycle ergometer for 5min and then a local phase with a circuit of 1 set of 15 repetitions in each exercise at 40% 1RM. The calibration test consisted of performing 1 set of 12 repetitions in each exercise with an intensity between 70% and 80% 1RM.
After a minimum period of 24h from PHASE 2, the main phase of data collection was carried out (PHASE 3). Before starting the execution of the exercise session, participants underwent the same warm-up as in the previous phase. All the exercises were performed for 3 sets of 12 repetitions in a circuit format with the load obtained in the confirmation of the 1RM performed in PHASE 2 (70–80% 1RM). The passive rest interval between exercises was of 30–45s and between sets was 90–120s. Participants were asked to follow the cadence 2:2 during the exercise execution. Finally, PHASE 4 consisted of returning to the laboratory 24 after the end of the training for the acquisition of new thermal images. To standardize the effect of the menstrual cycle on thermoregulatory responses, the experimental protocol was carried out using the first day of menstruation as a baseline. Therefore, data collection started up to 72h after the start of menstruation.
The thermography protocol to register the body regions of interest (ROIs) was performed with a FLIR® (T420) imager, with a measuring range of −20 to +120°C, 2% accuracy, sensitivity ≤0.05°C, an infrared spectral band of 7.5–13μm, autofocus and a refresh rate of 60Hz and resolution of 320×240 pixels, setting the emissivity at 0.98. The first thermogram was taken at rest before starting the exercise session and the second thermogram was obtained approximately 20min after the end of the training. The thermograms were obtained in a room with controlled temperature (21.3±0.9°C) and humidity (59.2±2.4%), as recommended by Fernández-Cuevas et al.20 An anti-reflective black background was used behind the participant to minimize any reflection from infrared radiation.24 To obtain the thermograms, an acclimation period longer than 10min was considered.25
Two thermograms of the anterior and posterior views were obtained (Fig. 2). Through Flir Tools® 4.1 software and following the recommendations of Marins et al.,26 the ROIs considered in this study were delimitated in the thermograms by selecting the corresponding areas of the biceps brachii (between the axillary line and 5cm above the elbow), the upper back (over both scapulae) and quadriceps (between a point 5cm above the upper edge of the patella and occupying the greatest length of quadriceps).
Statistical analysisSince the Shapiro–Wilk test showed that the data were normally distributed, a descriptive statistic was used with mean, standard deviation, and maximum and minimum values. To analyze the temporal effect of exercise, ANOVA with post hoc Tukey's test was performed. The unpaired t-test was used to compare the thermal responses between men and women. Statistical analyses were performed in SPSS Statistics Subscription® version 22, setting the level of significance at α=0.05.
ResultsTable 2 shows the Tsk values of the three ROIs considered in this study for every participant, indicating the mean values on the right (R) and left (L) sides and asymmetries at baseline (Δ°C).