10.15-11.00: Trial lecture 13.00-16.00: Public defense, Physiological and perceived exertion responses to training and match load in football: External and internal load, neuromuscular fatigue, muscle damage, and recovery Summary Background Have you seen football players running around the training field in sports bras over their uniforms? In this “vest”, the players have a tracking device that measures distance, speeds, and accelerations, and thus the external load on the body.
In periods with a tight match program and many training sessions, this tool can help the players manage how hard they should train and when they should rest. But what does it really mean that a player runs 10,000 m in training or in a match?
(Shutterstock/matimix) Mdethod In two different studies, we investigated how the external training load, measured with tracking devices, affects the individual player’s perceived (internal) load, how the external match load affects recovery after the match, and to what extent match load leads to minor damage to the muscle cells.
In the first study, we followed 18 elite series players on 21 sessions over a season, where the players wore tracking devices and where the players recorded perceived load on a scale from 1-10 after the session.
While the tracking devices measured an external load, i.e., pure displacement of the unit, perceived load (1-10 multiplied by the duration of the session) represents an internal load where individual characteristics such as height, weight, genetics, physical condition, daily form, etc., also play a part.
Results We saw a strong correlation between external load (measured with the tracking unit variable PlayerLoad™) and perceived load (measured as sRPE-TL). In practice, this means that the difference between a session with a typical low PlayerLoad™ and a session with a typical high PlayerLoad™ on average made up a doubling of the player’s sRPE-TL.
However, there were large individual differences between the players. Not only did sRPE-TL vary by ±20% for their average PlayerLoad™, they also had a ±24% variation in sRPE-TL response when they went from sessions with low to high PlayerLoad™.
These findings underline that it is essential to have an individual approach when monitoring players’ load. We also saw that the players agreed that some sessions were more strenuous than others, regardless of PlayerLoadTM and individual differences.
This means that there is a load in the sessions that is not captured by the tracking devices, and that it is therefore important to measure perceived load in addition to the load from the tracking devices.
In study II, we measured external load with motion sensors in a single match, and the subsequent recovery process (1–72 hours). Eighty-one players from 6 teams participated in the study and each played one match. Before and during the period after the match, we made measurements of creatine kinase (CK) and myoglobin which are blood markers for muscle damage, as well as countermovement jumps (CMJ), 30 m sprint and YOYO IR 1 test (YOYO) which are tests for physical performance.
On a small subgroup of players, we also took muscle biopsies of the lateral broad thigh muscle, where we measured the response to Heat Shock Proteins, a group of proteins that bind to and help stabilize damaged proteins.
The results showed that high-speed running (>4 m/s) affected blood markers for muscle damage, while PlayerLoad™ and total distance had an effect on 30-m sprint performance. This means that increased load in the match leads to longer recovery time, but also that it is important to use several types of load variables to measure match load. Surprisingly, we found no correlation between match load and CMJ, even though CMJ performance was significantly reduced after the match.
Finally, the examinations of the muscle biopsies show that Heat Shock Proteins bound to structural parts of the muscle cell, indicating mild muscle damage. One can therefore argue that the players are adapted to football matches, but that there are still load patterns in matches that exceed the threshold for what the muscles can tolerate and thus cause muscle damage.
The results of this dissertation can be helpful for clubs that use tracking devices or the sRPE-TL method to measure and monitor training and match load. Furthermore, the results can be an important input to the debate about how tight a match schedule is acceptable.
Welcome! 
Håvard Wiig has been a research fellow at the Department of Physical Performance at the Norwegian School of Sport Sciences. On April 22, 2024 he will defend his thesis Physiological and perceived exertion responses to training and match load in football: External and internal load, neuromuscular fatigue, muscle damage, and recovery, at NIH, Auditorium innsikt, 10:00 CET, and on YouTube (see below).
