No abstract

We compared measurements of high-intensity activity during field-based training sessions in elite soccer players of different playing positions. Agreement was appraised between measurements of running speed alone and predicted metabolic power derived from a combination of running speed and acceleration. Data was collected during a 10-week phase of the competitive season from 26 English Premier League outfield players using global positioning system technology. High-intensity activity was estimated using the total distance covered at speeds >14.4 km · h⁻¹ (TS) and the equivalent metabolic power threshold of >20 W · kg⁻¹ (TP), respectively. We selected 0.2 as the -minimally important standardised difference between methods. Mean training session TS was 478±300 m vs. 727±338 m for TP (p<0.001). This difference was greater for central defenders (~ 85%) vs. wide defenders and attackers (~ 60%) (p<0.05). The difference between methods also decreased as the proportion of high-intensity distance within a training session increased (R2=0.43; p<0.001). We conclude that the high-intensity demands of soccer training are underestimated by traditional measurements of running speed alone, especially in training sessions or playing positions associated with less high-intensity activity. Estimations of metabolic power better inform the coach as to the true demands of a training session.

The external-load measures that were found to be moderately predictive of RPE-TL in soccer training were HSR distance and the number of impacts and accelerations. These findings provide new evidence to support the use of RPE-TL as a global measure of training load in elite soccer. Furthermore, understanding the influence of characteristics affecting RPE-TL may help coaches and practitioners enhance training prescription and athlete monitoring.

We compared the accuracy of 2 GPS systems with different sampling rates for the determination of distances covered at high-speed and metabolic power derived from a combination of running speed and acceleration. 8 participants performed 56 bouts of shuttle intermittent running wearing 2 portable GPS devices (SPI-Pro, GPS-5?Hz and MinimaxX, GPS-10?Hz). The GPS systems were compared with a radar system as a criterion measure. The variables investigated were: total distance (TD), high-speed distance (HSR>4.17?m?s?1), very high-speed distance (VHSR>5.56?m?s?1), mean power (Pmean), high metabolic power (HMP>20?W?kg?1) and very high metabolic power (VHMP>25?W?kg?1). GPS-5?Hz had low error for TD (2.8%) and Pmean (4.5%), while the errors for the other variables ranged from moderate to high (7.5?23.2%). GPS-10?Hz demonstrated a low error for TD (1.9%), HSR (4.7%), Pmean (2.4%) and HMP (4.5%), whereas the errors for VHSR (10.5%) and VHMP (6.2%) were moderate. In general, GPS accuracy increased with a higher sampling rate, but decreased with increasing speed of movement. Both systems could be used for calculating TD and Pmean, but they cannot be used interchangeably. Only GPS-10?Hz demonstrated a sufficient level of accuracy for quantifying distance covered at higher speeds or time spent at very high power.

Heat dissipation during sport exercise is an important physiological mechanism that may influence athletic performance. Our aim was to test the hypothesis that differences exist in the dynamics of exercise-associated skin temperature changes between trained and untrained subjects. We investigated thermoregulation of a local muscle area (muscle-tendon unit) involved in a localized steady-load exercise (standing heels raise) using infrared thermography. Seven trained female subjects and seven untrained female controls were studied. Each subject performed standing heels raise exercise for 2 min. Thermal images were recorded prior to exercise (1 min), during exercise (2 min), and after exercise (7 min). The analysis of thermal images provided the skin temperature time course, which was characterized by a set of descriptive parameters. Two-way ANOVA for repeated measures detected a significant interaction (p = 0.03) between group and time, thus indicating that athletic subjects increased their skin temperature differently with respect to untrained subjects. This was confirmed by comparing the parameters describing the speed of rise of skin temperature. It was found that trained subjects responded to exercise more quickly than untrained controls (p < 0.05). In conclusion, physical training improves the ability to rapidly elevate skin temperature in response to a localized exercise in female subjects.