Overtime, the competitive distance among elite football teams has shortened, so the focus is currently on those aspects that can tip the scale to one side or the other. This has caused elite teams to incorporate specialists in different fields with the intention to seek the most comprehensive preparation possible while reducing injuries, one of the main limitations in regard to performance.

Training load (TL) monitoring is one of the main tools, as it allows us to assess fatigue, anticipating overloads and overtraining in order to minimise the risk of injury. In fact, there is a relationship between TL and the incidence of injuries,¹ which reflects the importance of its measurement. The TL can be differentiated between external and internal, defined respectively as the work performed by the athlete (e.g., distance covered, speed and acceleration, number of repetitions performed…) and the associated physiological response (e.g., rate of perceived exertion, heart rate, blood lactate, oxygen consumption…). Establishing the relationship between the two measures is important, while adjusting the external load to produce the programmed internal load is key when it comes to monitoring the evolution of the player’s state and their risk of injury as well.

Rate of Perceived Exertion

The monitoring and management of the internal load can be carried out using physiological variables such as blood lactate or heart rate.^2,3 However, these evaluation methods require equipment and human resources to which we do not always have access. For this reason, the rate of perceived exertion (or RPE) is widely used, a simple and precise tool, where the athlete only has to assess the feeling of fatigue and the intensity of exertion they felt during the session they just performed.

Internal load monitoring through the RPE or s-RPE (perceived exertion x length of session) of the session has proven to be a valid tool to quantify the training load, providing us with the load for that session. Thus, in a recent consensus document prepared by a group of experts on different methods for the control of TL, it was determined that the s-RPE is a easy to use and not expensive tool to interpret for a wide variety of physical activities.⁴

Nowadays, the scale with values ranging from 1 (rest) to 10 (maximum exertion) is widely used in the sports field, although originally exertion was valued in a range between 6 (no exertion) and 20 (maximum exertion). Besides, the correct thing to do is to assess the feeling of fatigue over the total load of the session 30 minutes after it has ended to ensure that the perceived exertion refers to the entire session and not to the intensity of the last exercise.⁵

Rate of Perceived Exertion in Footballers

RPE has been validated with football players,⁶ proving to be a good indicator of internal load for footballers,⁵ showing a strong correlation with objective internal load variables such as heart rate or blood lactate.⁷ In fact, RPE is the variable most used by professional football teams to quantify internal load.⁸ In this sense, it has been observed in a recent systematic review on methods based on the use of RPE in professional football, that s-RPE (as a measure of the full session load) is more used than RPE alone (as a measure of exercise intensity).⁹

In recent years, s-RPE has been applied to assess the injury risk in elite football. The link between s-RPE and injuries is reflected in studies such as the one conducted by the Australian Football Federation in which it was observed that the TL assessed through the s-RPE were higher in the 3 weeks prior to an injury than the season average.¹⁰ In this context, a recent study conducted by two European elite teams that used the s-RPE to quantify internal TL, has found that players who developed an acute load during preseason between 1,500-2,120 arbitrary units (AU) per week had a higher risk of injury than those who performed less than 1,500 AU.¹¹ Also, weekly changes between 350–500 AU were associated with a higher risk of injury, than when changes were less than 200 AU. The risk of injury was reduced when footballers were subjected to an acute:chronic load ratio between 1–1.25 AU.¹¹

Recently, a study published in the prestigious British Journal of Sports Medicine has evaluated the predictive value of internal load, assessed through the s-RPE, on the risk of non-contact injuries.¹² The authors analysed 171 players from 5 elite teams belonging to the UEFA Elite Club Injury Study and found that an acute:chronic load ratio of 1:3 or 1:4 was associated with an increased risk of injury in the following week, while it was not found for a ratio of 1:2. However, while the acute:chronic internal load ratio was associated with the risk of injury, this marker showed little value to predict and identify players who will suffer an injury a posteriori without a previous contact.

Conclusions

Internal load monitoring through s-RPE has proven to be a valid tool to reduce the risk of injury, and therefore, optimise performance. It’s easy implementation and reliability make the RPE a very effective tool to quantify the internal load of an athlete, although it is necessary that the players are previously trained to use the RPE. That’s why teams are starting to implement it in youth academies. The information provided will be of great help when planning sessions, especially when resources are limited, which is usually the case.

Javier S. Morales

References:

1. Drew MK, Finch CF. The Relationship Between Training Load and Injury, Illness and Soreness: A Systematic and Literature Review. Sports Med. 2016;46(6):861-83.
2. Algrøy EA, Hetlelid KJ, Seiler S, Stray Pedersen JI. Quantifying training intensity distribution in a group of Norwegian professional soccer players. Int J Sports Physiol Perform. 2011;6(1):70-81.
3. Eniseler N. Heart rate and blood lactate concentrations as predictors of physiological load on elite soccer players during various soccer training activities. J Strength Cond Res. 2005;19(4):799-804.
4. Bourdon PC, Cardinale M, Murray A, Gastin P, Kellmann M, Varley MC, Gabbett TJ, Coutts AJ, Burgess DJ, Gregson W, Cable NT. Monitoring Athlete Training Loads: Consensus Statement. Int J Sports Physiol Perform. 2017;12(Suppl 2):S2161-S2170.
5. Impellizzeri FM, Rampinini E, Coutts AJ, Sassi A, Marcora SM. Use of RPE-based training load in soccer. Med Sci Sports Exerc. 2004;36(6):1042-7.
6. Coutts A, Reaburn P, Murphy A, Pine M, Impellizzeri FM. Validity of the session-RPE method for determining training load in team sport athletes. J Sci Med Sports. 2003;6:525.
7. Coutts AJ, Rampinini E, Marcora SM, Castagna C, Impellizzeri FM. Heart rate and blood lactate correlates of perceived exertion during small-sided soccer games. J Sci Med Sport. 2009;12(1):79-84.
8. Akenhead R, Nassis GP. Training Load and Player Monitoring in High-Level Football: Current Practice and Perceptions. Int J Sports Physiol Perform. 2016;11(5):587-93.
9. Rago V, Brito J, Figueiredo P, Costa J, Krustrup P, Rebelo A. Internal training load monitoring in professional football: a systematic review of methods using rating of perceived exertion. J Sports Med Phys Fitness. 2020;60(1):160-171.
10. Lu D, Howle K, Waterson A, Duncan C, Duffield R. Workload profiles prior to injury in professional soccer players. Sci Med Football. 2017;1:237-43.
11. Malone S, Owen A, Newton M, Mendes B, Collins KD, Gabbett TJ. The acute:chonic workload ratio in relation to injury risk in professional soccer. J Sci Med Sport. 2017;20(6):561-565.
12. McCall A, Dupont G, Ekstrand J. Internal workload and non-contact injury: a one-season study of five teams from the UEFA Elite Club Injury Study. Br J Sports Med. 2018;52(23):1517-1522.