The influence of changes in acute training load on daily sensitivity of morning-measured fatigue variables in elite soccer players

Thorpe RT, Strudwick AJ, Buchheit M, Atkinson G, Drust B, Gregson W. The influence of changes in acute training load on daily sensitivity of morning-measured fatigue variables in elite soccer players. IJSPP, In press

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Purpose To determine the sensitivity of a range of potential fatigue measures to daily training load accumulated over the previous two, three and four days during a short in-season competitive period in elite senior soccer players (n=10).

Methods Total high-speed running distance, perceived ratings of wellness (fatigue, muscle soreness, sleep quality), counter-movement jump height (CMJ), submaximal heart rate (HRex), post-exercise heart rate recovery (HRR) and heart rate variability (HRV: Ln rMSSD) were analysed during an in-season competitive period (17 days). General linear models were used to evaluate the influence of two, three and four day total high-speed running distance accumulation on fatigue measures.

Results Fluctuations in perceived ratings of fatigue were correlated with fluctuations in total high-speed running distance accumulation covered on the previous 2-days (r=-0.31; small), 3-days (r=-0.42; moderate) and 4-days (r=-0.28; small) (p<0.05). Changes in HRex (r=0.28; small; p= 0.02) were correlated with changes in 4-day total high-speed running distance accumulation only. Correlations between variability in muscle soreness, sleep quality, CMJ, HRR% and HRV and total high-speed running distance were negligible and not statistically significant for all accumulation training loads.

Conclusions Perceived ratings of fatigue and HRex were sensitive to fluctuations in acute total high-speed running distance accumulation, although, sensitivity was not systematically influenced by the number of previous days over which the training load was accumulated. The present findings indicate that the sensitivity of morning-measured fatigue variables to changes in training load is generally not improved when compared with training loads beyond the previous days training.



Player tracking technology: half-full or half-empty glass?

Buchheit M & Simpson BM. Player tracking technology: half-full or half-empty glass? IJSPP, In press

This paper summarizes the main points of my talk in Aspire last year (Monitoring Load conference, Doha, Qatar, 2016) where I, among others, highlited the limitations of the metabolic power concept

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Abstract. With the ongoing development of (micro) technology, player tracking has become one of the most important components of load monitoring in team sports. The three main objectives of player tracking are the following: i) better understanding of practice (provide an objective, a posteriori evaluation of external load and locomotor demands of any given session or match), ii) the optimisation of training load patterns at the team level and iii) decision making on individual players training programs to improve performance and prevent injuries (e.g., top-up training vs. un-loading sequences, return to play progression). This paper, discusses the basics of a simple tracking approach and the need for the integration of multiple systems. The limitations of some of the most used variables in the field (including metabolic power measures) will be debated and innovative and potentially new powerful variables will be presented. The foundations of a successful player monitoring system are probably laid on the pitch first, in the way practitioners collect their own tracking data, given the limitations of each variable, and how they report and utilize all this information, rather than in the technology and the variables per se. Overall, the decision to use any tracking technology or new variable should always be considered with a cost/benefit approach (i.e., cost, ease of use, portability, manpower / ability to impact on the training program).


Figure. Example of Force load symmetry in a players during his return to play period following a right ankle sprain. The symmetry (with errors bars standing for typical error of measurement8) is calculated from the Force load of all foot impacts during all accelerated running phases (>2m.s-2) of each session. The star represents the date of the injury.


Metabolic power: powerful enough to drive Ferraris?

After many requests following my talk in Aspire last year (Monitoring Load conference, Doha, Qatar, 2016) where I takled the metabolic power concept, I have just put together a written version of this specific section (that will also partly be inlcuded in a IJSPP paper written with Ben Simpson now available here)

Since Osgnagh et al. in 2010,13 who showed the potential application of the metabolic power (MP) concept8 for load monitoring in soccer, the interest for this variable has grown exponentially and is now used across many other team sports.6, 7, 12, 16 In fact, most GPS brands offer now the ability to monitor players’ MP, and a majority of practitioners use this variable when reporting.1 While we have been the firsts to be excited about the potential of this monitoring approach, we have since reconsidered our opinion and question now its usefulness in the field to monitor elite players (i.e., “Ferraris”). This is essentially related to i) recent research findings questioning its validity in the context of team sports-specific movements and ii) the fact that it is only an incomplete metabolic measure of internal load and probably too broad a marker of external load.

What do we actually measure?

It has now been shown by four distinct and independent research groups that locomotor-related MP assessed via either GPS or local positioning system (PGPS or Pmet in the figure below) differs largely from the true metabolic demands as assessed via indirect calorimetry (VO2 measures, PVO2). PGPS was actually reported to be very largely greater than PVO2 during walking,3 but very largely lower during shuttle runs at low speed15 and during soccer-,4 rugby-11 or team-sports3 specific circuits.


While some may see the consistency of such conclusions as a kind of consensus, Osgnach et al. wished to write a letter to the editor to defend their approach and criticize our methodology.14 Since we were not given the chance to respond to this letter by the IJSM editor (“you will not be invited to respond to this letter, but I am sure that you will discuss directly this interesting issue with the di Prampero group”), we wished to comment on their main critics in the present post. This should clarify some discussions and confirm the limitations of MP in the context of interest, i.e., monitoring team-sports specific efforts with the available technology on the market.

  • Resting VO2
    • Osgnagh et al.: “Buchheit et al. have included resting VO2 in their calculations; using net VO2 as in the original methodology would reduce the difference observed and PGPS won’t appear to be underestimated anymore.”14
    • Response: we have in fact used net VO2, as clearly written p1151, 2nd paragraph “Average net VO2 and the respiratory exchange ratio (RER) were calculated for each of the three 1-min efforts and the following 30-s recovery periods”4


  • Anaerobic energy contribution
    • Osgnagh et al.: “Anaerobic energy contribution is not appropriately accounted for in the calculation (the intensity of some efforts may be greater than VO2max, so that they are missed in the overall metabolic cost).”14
    • Response: Agree. But in this case, the actual (true) metabolic demands would have been even greater than those measured, which suggests that the PGPS underestimation would have actually been even greater than that reported in our paper!4


  • Impact of non-locomotor actions
    • Osgnagh et al.: “as shown in Buchheit’s Figure 2, VO2 increases markedly at several points, while the simultaneously determined MP remains close to zero.”14 They suggest that something was wrong with our data.
    • Response: Soccer as most other team sports often includes intense but static movements (passing a ball for example, as in our circuit). It is therefore obvious to observe a rise in VO2 that is not associated with locomotor movements and in turn, changes in MP. This is an important limitation of MP – which may only reflect locomotor-related metabolic activity. But if that was the case, what would be the value of such an impartial measure of metabolic load? This is at odds with all attempts to use MP outputs for overall load monitoring or nutritional (post training/matches recovery) guidelines.6


  • Sampling frequency
    • Osgnagh et al.: “The low sampling frequency of the GPS device used is problematic and explains the underestimation of PGPS.”14
    • Response: while we agree that 4 Hz as used in our study can be considered as low, we don’t believe that this may be the cause of the underestimation since the other researchers have all reported the same underestimation using higher sampling frequencies (i.e., 500,15 1011 and 53 Hz). Note also that we have shown that sampling frequency per se was not the most important factors when it comes to precision and validity.5


Added value to load monitoring systems?

Considering that the agreement between PGPS and PVO2 has only been shown to be acceptable during continuous and linear jog and runs (but neither during walking nor intermittent changes of direction runs)3, the metabolic underestimation may be related to the fact that the current equation initially developed for maximal and linear sprint acceleration8 may not be well suited for team-sport specific running patterns (e.g., including rest, irregular step frequency and stride length, turns, upper body muscle activity, static movements).4


This suggests that the value of PGPS per se to monitor training load in team sports may be questionable. Its usefulness may also be limited with respect to practitioners’ expectations in the field. In fact, practitioners are likely seeking for:

  • Overall estimates of internal load, which are satisfactorily assessed through HR and RPE measures1 – information on the metabolic load of exclusively locomotor-related actions as with PGPS may not be comprehensive enough.
  • Precise measures of external load, which directly relate to specific mechanical constraints on players’ anatomy, which, in turn target specific muscle groups. This has direct implications for training, recovery and injury risk. However:
    • PGPS is clearly dissociated from actual muscle activation, as exemplified by very large variations in the PGPS/EMG ratio during accelerated vs. decelerate running.10


  • PGPS, if it was to be used as a global marker of mechanical work, wouldn’t allow deciphering the underlying mechanisms of the load – we rather use distance while accelerating, decelerating and while running at high-speed since those variables may relate directly to the load of specific muscle groups.


  • Injuries are most generally related to inappropriate volumes of accelerations2 or high-speed running;9 there is in contrast little evidence to suggest that spikes in overall energy consumption per se may play a role in injury etiology.


Until new evidences are provided regarding the validity of PGPS as a valid measure of overall energy expenditure during team-sport specific movements, and given the conceptual limitations (difficulties in deciphering the underlying mechanisms of the load), metabolic power assessed via the current technology (PGPS) may not be as powerful as we though to drive Ferraris.


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