Should we calculate training loads using metabolic power: predicted from speed and acceleration, jus

Training Loads

The importance of small sided games is emphasised in modern football training regimes. In the past it was common to have football coaching prescribing track and field style running sessions for their football players. Due to recent scientific testing and literature it has become evident that such training does not transfer effectively to the game of football (Dellal et al., 2011; Impellizzeri et al., 2007).

The steady state lactate during running specific distances, heart rate zones and mechanical differences are completely different when comparing track running to game play. Contact time between the practitioner and the players is generally little and thus the importance of maximising the quality of work is paramount. Since time is limited, small sided games offer the best buck. Such games not only improve physiological adaptations which are similar to the actual game but also the practitioner can also improve the player’s tactical and technical components.

Coaches using small sided games are faced with the difficulty of monitoring player individual training loads. The challenge lies within the endless variations multidirectional team sports have to offer. A change in pitch dimensions, time intervals vs. rest ratios, conditions, motivation, amount and quality of players all have an effect on the external training loads of a player.

The importance of the coach receiving detailed and accurate individual player training load is required to prescribe the most appropriate training for the individual player to be in peak form on match day. Apart from the player performing at his best on match day, understanding the loads the player is receiving is important to prevent injuries. Planning training loads to overload progressively is one of the principles of sport in which if ignored the risk of injuries and occurrence of overtraining are highly increased (Brenner, 2007).

“By failing to prepare, you are preparing to fail." - Benjamin Franklin

As GPS units are becoming more and more popular and within reach of coaches and practitioners the ability to measure accurately external training loads during multi directional team sports has become possible. At present a divide within the literature is present on how to calculate the actual training loads. Having Martin Buccheit being an advocate for the speed zone method and di Prampero together with Osgnach being advocates of the speed zone method with accelerations and decelerations taken into account. This article blog will highlight the two sides of the divide.

Speed Zones

The common use of GPS units by coaches has been to identify the distance and time covered at specific speed zones. The arbitrary speed zones vary between practitioners so there is no one specific method. After investigating the literature, most commonly zones are put in such a manner:

Speed Zones

0 - 6.9km/hr (walking)

7.0 - 12.9km/hr (jogging)

13.0 - 17.9km/hr (running)

18.0 - 20.9km/hr (high-intensity running)

<21km/hr (sprinting)

An important consideration when choosing speed zones is highlighted in a study by Gabbett, J in 2015 wherein the argument between relative and absolute speed zones is brought up. Practitioners using absolute speed zones are underestimating the players efforts according to this study. The underestimation occurs due to the players having different individual peak velocities hence the effort at a certain speed zone of one player might be less for another at the same zone. Practitioners at clubs are recommended to use the absolute zones for game play so the practice level is compared but also the relative zones to better administrate recovery to work ratios.

Coaches use the overall time in percentage and the percentage of overall distance spent at each zone whilst performing training exercises or during match play. From the amounts covered in each zone the energy cost as metabolic power can be calculated for each individual in the team. By obtaining the energy cost of each individual from various training exercises, the coach can have a better informed judgement on what to prescribe.

Acceleration and Deceleration

Acceleration and deceleration are part of the nature of multidirectional team sports. Whenever a player is changing direction to react to the given match actions there is a deceleration from the current course to an acceleration towards a new course. When using only speed zones for measuring external load, the effort when decelerating and accelerating is underestimated. As a player is accelerating to quickly decelerate before reaching a high speed zone the traditional speed zone method does not take into account the effort of accelerating as the speed reach would be that of the lower speed zones but at a higher effort.

Research on acceleration and deceleration is very scarce for the reason that only recently with the new versions of GPS units which work at 10Hz are we able to receive reliable sources of measurement (Varley, et al 2012). Work by di Prampero et al. (2005) have highlighted the possibility of measuring the external load of a player taking account the acceleration and deceleration. This is possible by using the energy cost of running uphill at a constant speed which is equivalent to the same energy cost when a player is accelerating.

Controversy

When Osgnach et al. (2010) investigated Serie A players over an entire season the authors looked into the difference between calculating energy cost using speed zones and instantaneous energy cost which included accelerations. When energy cost included accelerations it was concluded to have two to three times higher energy cost when compared to energy cost from speed zones. The findings of such study highlighted the underestimation of the external load on players when practitioners used speed zones. On the contrary to Osgnach et al. (2010) findings, Buchheit et al. (2015) using 3 sets of 1 minutes bouts with 4Hz GPS units conclude that instantaneous energy cost which included the accelerations underestimated the energy cost of soccer specific drills when compared to speed zones external load cost calculations.

It is important to take note on how several studies looking into GPS reliability for measuring instantaneous velocity have found that GPS units under 10Hz are not suitable and have poor validity (Coutts, & Duffield, 2010). The reliability reported with 10Hz units was six times higher than that of 5Hz units (Varley, Fairweather, & Aughey, 2012). Osgnach et al. (2010) have used 25Hz technology as compared to 4Hz technology Buchheit et al. (2015) have used. This is one of the points which could be considered as a flaw in Buchheit et al. (2015) study. Another point to pick up on is on how Buchheit et al. (2015) have used specific, fixed drills to compare such methods as compared to Osgnach et al. (2010) in which league matches were used. Movements in a specific repeated drill could have much more predictable movement than a match were movements and actions are more unpredictable. Also the effort and performance of the players is somewhat different when performing a drill in training as compared with a competitive under pressure environment such of a league match.

The main reasoning from Buchheit against the instantaneous power calculations which include the acceleration effort is that different players have different technique and ways of running which would have different energy expenditure properties. This is important when considering that Osgnach, et al. (2015) calculations are based upon an energy cost for typical uphill running technique.

Currently the speed zone method is most popular by practitioners in the field. This could be for various reasons, such as the reduced cost of GPS units that is lower than 10Hz in frequency and for convenience since it is an easier method. Instantaneous power to add acceleration and deceleration energy cost with the total energy cost of sessions to calculate training load is gaining popularity. Having the accurate training loads is imperative for the practitioner so as to avoid maladaptations and injuries and also for players to reach peak performance on the day (match day). It is also imperative to realise that football related actions such as heading the ball, passing or shooting, tackling, dribbling and traveling with the ball are actions which are neglected when using such systems to measure load. Therefore apart from good measurement of training load a good coaching eye is always important for optimum results.

Reference:

Gabbett, T. J. (2015). Use of relative speed zones increases the high-speed running performed in team sport match play. Journal of Strength & Conditioning Research, 29(12), 3353-3359.

Varley, M. C., Fairweather, I. H., & Aughey1, 2, R. J. (2012). Validity and reliability of GPS for measuring instantaneous velocity during acceleration, deceleration, and constant motion. Journal of Sports Sciences, 30(2), 121-127.

Di Prampero, P. E., Fusi, S., Sepulcri, L., Morin, J. B., Belli, A., & Antonutto, G. (2005). Sprint running: a new energetic approach. Journal of Experimental Biology, 208(14), 2809-2816.

Osgnach, C., Poser, S., Bernardini, R., Rinaldo, R., & Di Prampero, P. E. (2010). Energy cost and metabolic power in elite soccer: a new match analysis approach. Medicine Science Sports and Exercise Journal, 42(1), 170-178.

Varley, M. C., Fairweather, I. H., & Aughey, R. J. (2012). Validity and reliability of GPS for measuring instantaneous velocity during acceleration, deceleration, and constant motion. Journal of Sports Sciences, 30(2), 121-127.

Coutts, A. J., & Duffield, R. (2010). Validity and reliability of GPS devices for measuring movement demands of team sports. Journal of Science and Medicine in Sport, 13(1), 133-135.

Dellal, A., Hill-Haas, S., Lago-Penas, C., & Chamari, K. (2011). Small-sided games in soccer: amateur vs. professional players' physiological responses, physical, and technical activities. Journal of Strength & Conditioning Research, 25(9), 2371-2381.

Rampinini, E., Impellizzeri, F. M., Castagna, C., Abt, G., Chamari, K., Sassi, A., & Marcora, S. M. (2007). Factors influencing physiological responses to small-sided soccer games. Journal of Sports Sciences, 25(6), 659-666.

Brenner, J. S. (2007). Overuse injuries, overtraining, and burnout in child and adolescent athletes. Journal of Paediatrics, 119(6), 1242-1245.