## 2 Materials and Methods  
### Procedures and Data Collection  
Forty players (mean \(\pm\) SD; age 29.4 \(\pm\) 5.8 years; height 175.3 \(\pm\) 5.2 cm; body mass 76.5 \(\pm\) 8.2 kg) classified from all offensive and defensive position groups (9 central defenders, 8 fullbacks, 10 central midfielders, 6 wide midfielders, 7 forwards) from the same elite soccer club competing in the French Ligue 2 participated in one full-season (2017/2018) data collection. The study was conducted according to the requirements of the Declaration of Helsinki. Participants gave their written informed consent to participate in the study. Approval for the study was obtained from the Club as player's data were routinely collected throughout the season.  
The training workload, perceptive well-being questionnaires and injury data were monitored over the pre-season period and during the entire competitive period from June 2017 to May 2018, taking into account the different breaks between these periods, the international trucks and the winter truce. A total of 245 training sessions, 38 Domino's Ligue 2 matches, 2 Coupe de la Ligue matches and 3 Coupe de France matches were recorded and analyzed. Altogether, the average recording time in training and match was 68 \(\pm\) 24 min and 105 \(\pm\) 11 min, respectively. The average distance covered by all players for both training session and match was 4817 \(\pm\) 1965 m and 7694 \(\pm\) 1527 m, respectively; and the average duration was 65 \(\pm\) 13 min per training session and 78 \(\pm\) 16 min per match.  
During those periods, 142 injuries were inferred from the training notes containing the list of injured players for each training session. The injuries concerned 33 different players. Figure 1 represents the number of injuries per players: 12 players were injured only once, 5 players were injured 6 times and 1 player had 12 injuries. It is important to note that the real injury times and reasons were not known. It was alleged that when a player was referred as injured in a training session, it was in fact at the last training session that his injury really occurred. The injury labels contain therefore some uncertainty that was not taken into account in this study.  
Various types of training load features (see Table 1) regarding a professional soccer club were collected from 40 players during official competitive matches, pre-season preparation matches, before, during and after training sessions. A first set of features concerned the player's activity using a GPS tracking system. The GPS system allows real-time player tracking and an early a posteriori analysis for coaching staff. This first set of features reflects the external training load, i.e., the objective physical work performed by the player. The player's physical activity during each training session and match  
Figure 1: Number of injuries per players.  
was measured using a portable 10 Hz GPS system (Optimeye S5, Catapult Innovations, Melbourne, Australia) integrated with a 100 Hz triaxial accelerometer and a gyroscope. The accelerometer and gyroscope components combined with 10 Hz GPS systems have shown acceptable levels of reliability and validity in team sports for distance and high-speed distance-based metrics [20; 21]. Four main external load features were measured: maximum speed, total distance covered, and number of accelerations and decelerations. Based on the dedicated literature [22; 23] the following external training load features were retained: the total distance travelled in each specific speed zone (0-1 km/h, 0-6 km/h, 6-15 km/h, 15-20 km/h, 20-25 km/h, \(>\) 25 km/h) and the PlayerLoad TM (athlete's mechanical fatigue index according to [PERSON], [PERSON], and [PERSON] [24]), which is a modified vector magnitude expressed as the square root of the sum of the squared instantaneous rated of change in acceleration in each of the three planes and divided by 100.