Response of skin temperature, blood ammonia and lactate during incremental exercise until exhaustion in elite athletes.

The study aimed to evaluate the lower limb skin temperature (Tsk) and blood concentrations of lactate (LA) and ammonia (NH3) during exercise and recovery. Eleven elite sprint athletes (25 ± 3.4 yrs) and 11 elite endurance athletes (24.45 ± 5.4 yrs) performed an incremental running test until exhaustion. Body composition was estimated using the DXA method. Thermograms of the anterior and posterior surfaces of the lower limbs were recorded at rest, before each test stage (every 3 min, starting from 10 km h-1 and increasing by 2 km h-1), and in the 5th, 10th, 15th, 20th, and 30th minute of recovery. Endurance athletes had a higher maximum oxygen uptake than sprint athletes (5.0 ± 0.7 vs 4.3 ± 0.4 l·kg-1, p = 0.018), lower percentage of lean content (79 ± 2 vs 83 ± 2%, p < 0.001), and a higher percentage of fat content in the lower limbs (17 ± 2 vs 12 ± 2%, p < 0.001). In both groups, a significant decrease in Tsk was observed compared to resting value (endurance athletes-31.5 ± 0.6 °C; sprint athletes-32.3 ± 0.6 °C), during exercise (p < 0.001) and rewarming during recovery (p < 0.001). However, endurance athletes had a lower Tsk than sprint athletes at the exhaustion point (30.0 ± 1.1 vs 31.6 ± 0.8 °C, p < 0.05) and the pattern of change in Tsk differed between groups (p < 0.001). Tsk in the endurance athletes group decreased throughout the exercise protocol and returned more rapidly to initial values during recovery, while Tsk in the sprint group stabilised between moderate intensity and exhaustion, recovering more slowly after exercise. Both LA (endurance athletes-max 10.2 ± 1.5; sprint athletes-max 10.1 ± 1.4 mmol⋅L-1, p < 0.001) and NH3 (endurance athletes-max 75.6 ± 11.5; sprint athletes-max 76.7 ± 9.0 mmol⋅L-1, p < 0.001) increased during exercise and decreased during recovery (p < 0.001). During exercise, lower levels and slower increases in LA were observed during exercise in the endurance athletes' group (p < 0.05). A negative correlation was revealed between Tsk and fat percentage (r = -0.43 to -0.71, p < 0.05). Tsk was positively correlated with LA during recovery (r = 0.43 to 0.48, p < 0.05), and negatively during recovery (r = -0.45 to -0.54, p < 0.05). Differences between groups in maximum aerobic capacity, the pattern of change in Tsk, and the correlation between Tsk and LA suggest that individuals who decrease less Tsk during exercise and higher Tsk during recovery are those with better aerobic capacity. In addition, athletes with less body fat dissipate heat from their tissues more efficiently.

Physically active men with high brown adipose tissue activity showed increased energy expenditure after caffeine supplementation.

This study measured the effect of caffeine on brown adipose tissue (BAT) activity and the energy expenditure (EE) of subjects with high (HBAT) or low (LBAT) activation. We performed a quasi-experimental double-blind protocol in which 24 physically active healthy men were measured (age: 24.1 ± 6.0 yrs; BM: 75.3 ± 14.4 kg; HT: 171.8 ± 5.9 cm; BMI: 25.5 ± 4.9 kg/m2). Infrared thermography (IRT) protocol was used to separate the participants into the groups according to the BAT activation: high (HBAT; n = 11) and low (LBAT; n = 13). All participants ingested a single supplement caffeine capsule (CAF) of 375 mg (~5 mg/kg BM) or placebo (PLA). Our experimental protocol measured two groups (HBAT and LBAT) under two conditions (CAF and PLA), with intake 30-min before the data collection. BAT activity lasted 60-min (0, 10, 20, 30, 40, 50, 60 min) and was estimated by IRT in subclavicular (Δ SCV) and external (Δ EXT) regions of interest (ROI) and EE by indirect calorimetry. The main results indicated that HBAT at 40-min showed an increased EE versus the other groups and conditions (p = 0.009). There was a significant difference for BAT activation at the 30 (p = 0.019), 40 (p = 0.009), 50 (p = 0.007) and 60 min (p = 0.012) between HBAT-CAF vs. LBAT-CAF. There was also a significant difference at the 20 (p = 0.024), 30 (p = 0.036), 50 (p = 0.05) and 60 min (p = 0.011) between HBAT-CAF vs. HBAT-PLA. In conclusion CAF intake (≈5 mg) increases the thermogenic activity of BAT in healthy young men and increases EE in HBAT subjects.

Modeling the basin of attraction as a two-dimensional manifold from experimental data: applications to balance in humans.

We present a method of modeling the basin of attraction as a three-dimensional function describing a two-dimensional manifold on which the dynamics of the system evolves from experimental time series data. Our method is based on the density of the data set and uses numerical optimization and data modeling tools. We also show how to obtain analytic curves that describe both the contours and the boundary of the basin. Our method is applied to the problem of regaining balance after perturbation from quiet vertical stance using data of an elite athlete. Our method goes beyond the statistical description of the experimental data, providing a function that describes the shape of the basin of attraction. To test its robustness, our method has also been applied to two different data sets of a second subject and no significant differences were found between the contours of the calculated basin of attraction for the different data sets. The proposed method has many uses in a wide variety of areas, not just human balance for which there are many applications in medicine, rehabilitation, and sport.