Training Load: Differentiating Training Volume and Training Dose

in International Journal of Sports Physiology and Performance

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Louis PassfieldFaculty of Kinesiology, University of Calgary, Calgary, AB, Canada
School of Sport and Exercise Sciences, University of Kent, Canterbury, United Kingdom

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Juan M. MuriasFaculty of Kinesiology, University of Calgary, Calgary, AB, Canada

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Massimo SacchettiDepartment of Movement, Human and Health Sciences, University of Rome “Foro Italico,” Rome, Italy

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Andrea NicolòDepartment of Movement, Human and Health Sciences, University of Rome “Foro Italico,” Rome, Italy

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Dear Editor,

We would like to thank our colleagues who have written to comment1,2 on our recent review about the validity of the training load (TL) concept,3 particularly given their extensive previous scientific and practical contributions on this topic. We are pleased to have the opportunity to extend discussion of the topic further in this reply. We suspect that how TL is conceptualized may lead to important differences in perspective as we find ourselves in broad agreement with several of the points raised in both letters. Therefore, we will respond by briefly outlining our interpretation of the TL concept and the rationale for linking this to an acute performance decrement (APD) and then addressing some specific points that were raised.

Most discussions of the concept of TL begin with the seminal work of Banister et al,4 who proposed that training-induced fatigue could be linked to subsequently observed gains in performance (fitness). Banister’s work was based on fundamental principles of training theory,5,6 and therefore, we conceptualized the TL in the same manner but as a single training dose. The principles of training theory propose that a training session constitutes an overload that causes a training stress and fatigue, which, in turn, provides a signal for adaptation or overcompensation that occurs during the ensuing recovery period (Figure 1). The training session is considered a training dose, and the resultant training adaptations increase fitness and enhance performance. Indeed, the representation of this training process is often described by its effects on performance, that is, an APD occurs in response to the training dose, and then in recovery, performance is restored progressively to an augmented level (Figure 1). Banister et al’s4 thesis was that chronic changes in performance could be modeled as the integrated effects of training fatigue and fitness. As benefits to performance accumulate largely after the session in the recovery period, Banister’s model suggests that the APD observed at the end of a training session is linked to subsequent fitness gains. However, instead of measuring training-induced fatigue or an APD, Bannister et al, instead, modeled the training dose, which they calculated using arbitrary training impulse units (TRIMPs). Thus, the association between TRIMPs (as an indicator of the training dose) and APD was conceptualized by Bannister et al4 but not verified experimentally. Accordingly, we agree that we did not demonstrate the validity of APD as a TL criterion as we were, instead, testing its implicit relationship in the TL model.

Figure 1
Figure 1

—A principles-of-training diagram showing how a training dose leads to an acute performance decrement (black circle). A low training dose is theorized to result in a smaller decrement and performance benefit compared with a larger training dose.

Citation: International Journal of Sports Physiology and Performance 17, 10; 10.1123/ijspp.2022-0247

Considering an athlete’s TL in the form of a training dose that results in an APD is common practice,48 but it may be useful to discuss this in its relation to the broader TL concept. Jeffries et al9 have recently conceptualized TL as the amount of physical training done or experienced by athletes, that is, not solely as a training dose. This very broad definition of TL implies that the training dose is a subcomponent of TL. We can embrace this broad definition of TL but suggest that there is, then, a need to distinguish between different constructs of TL to relate it to training stress and effects and performance outcomes. An example wherein such a distinction has already been made is between internal and external TL.9 If a distinction is made between 2 further TL constructs of training volume and the training dose, controversy regarding the validity of currently used TL metrics may be ameliorated. Traditionally, TL metrics have broadly tended to reflect the volume of training (by multiplying exercise intensity and duration),10 and this includes the criterion measure of total V˙O2 adopted by Wallace et al.11 However, the same volume of training can be obtained by very different combinations of exercise intensity and duration—potentially leading to very different training effects and performance outcomes.3,12 Equally, very different volumes of chronic training can lead to similar performance outcomes.1315 Accordingly, in our review we highlighted the importance of the distinction between the amount (volume) of training and the dose of training and focused specifically on the dose of training.3

Slattery et al2 wrote in defense of their earlier study,11 which sought to establish the validity of specific TL metrics. In their letter, Slattery et al sensibly justified their use of total V˙O2 as a criterion measure for assessing the metabolic cost of aerobic exercise. In this respect, we are in complete agreement with our colleagues. Measuring total V˙O2 and related parameters, such as total work done (TWD), is helpful in quantifying the energy expenditure or volume of a training session. However, our point was that the metabolic cost of training does not equate to a training dose, and therefore, its use to validate TL metrics remains unjustified. Total V˙O2 (or TWD) dissociates extensively from the pattern of APD observed following a variety of training sessions as we described previously.3,16 In addition, total V˙O2 (or TWD) is not closely associated with the effort of a training session when continuous and intermittent exercise are compared.3,17 Furthermore, V˙O2 is not particularly sensitive to a range of stressors that are known to have large detrimental effects on performance, like muscle damage or fatigue, prior exercise, hyperthermia, and hypoxia.3 Indeed, paradoxically, under these circumstances, a lower total V˙O2 is accompanied by premature exhaustion of the athlete when compared with control conditions. Collectively, these findings point to a weak association between total V˙O2 and exercise-induced changes in performance.

The fact that V˙O2 is not sensitive to a variety of stressors that affect both training effects and performance outcomes may indicate that V˙O2 per se does not capture some of the features needed to quantify the training dose effectively. Indeed, Wallace et al11 acknowledged that factors other than V˙O2 may affect TL and specifically pointed to muscle damage prior to exercise as an example of a stressor not captured by V˙O2. As an alternative, we have outlined how respiratory frequency is sensitive to a variety of stressors affecting performance, including muscle damage, especially during cycling exercise.18 Unlike V˙O2, respiratory frequency is closely associated with perceived exertion17,18 and seems to be associated with APD,3 although further studies are required to corroborate this notion.

The strong association between total V˙O2, TWD, and several other TL metrics (eg, session rate of perceived exertion and TRIMP) suggests that they all broadly quantify the training volume rather than the training dose.11,19 This observation creates a validity issue when evaluated against the framework proposed by Jeffries et al9 as measures of internal TL are supposed to be closely associated with training effects and sport performance outcomes. In contrast, we found that the NASA-Task Load Index did track consistently with APD, our proxy for a training dose in one of our studies.16 But, primarily, we contend that there is a need for new TL metrics to be developed that differentiate training volume and training dose and correspond to their very different implications for training monitoring.

Why do we continue to find cause for concern with TL where our colleagues do not? Since Banister’s study, TRIMPs have been adopted by practitioners and scientists as a metric of TL, and thus, a key point in our review was to highlight that they have never been validated for this purpose. Indeed, as we pointed out, a consistent theme for the TL metrics in common use today is that they have not been validated adequately. When we examined experimentally the underpinning of the model, which relates a training dose to its fatigue or APD element, our findings suggested that commonly used TL metrics do not quantify the training dose effectively.3,16,20 Although we agree with our colleagues that these findings may not directly challenge the validity of the TL concept, they do question the validity of the TL metrics evaluated—when TL is conceptualized as a training dose. The validity of TL metrics as a representation of the training dose remains untested.

In conclusion, we are grateful for this opportunity to explore some of the issues related to the validity and concept of TL. Specifically, we hope that our response has helped clarify why our recent findings reinforced our concern with the validity of commonly used TL metrics. Finally, we hope that this reply and related discussions contribute to the scientific debate on the TL concept and its subcomponent structure and help shape future experimental work.

References

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    McLaren SJ, Shushan T, Schneider C, Ward P. Comment on Passfield et al.: validity of the training-load concept. Int J Sports Physiol Perform. Published online July 2022. doi:10.1123/ijspp.2022-0147

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 2.

    Slattery KM, Wallace LK, Coutts AJ. Comment on Passfield et al: defending the use of oxygen uptake as a criterion measure for training load. Int J Sports Physiol Perform. Published online July 2022. doi:10.1123/ijspp.2022-0154

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 3.

    Passfield L, Murias JM, Sacchetti M, Nicolò A. Validity of the training-load concept. Int J Sports Physiol Perform. 2022;17(4):507514. PubMed ID: 35247874 doi:10.1123/ijspp.2021-0536

    • Crossref
    • PubMed
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  • 4.

    Banister EW, Calvert TW, Savage MV, Bach TM. A systems model of training for athletic performance. Aust J Sports Med. 1975;7:5761.

  • 5.

    Issurin VB. New horizons for the methodology and physiology of training periodization. Sports Med Auckl NZ. 2010;40(3):189206. doi:10.2165/11319770-000000000-00000

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 6.

    Bompa TO, Buzzichelli CA. Periodization: Theory and Methodology of Training. 6th ed. Human Kinetics; 2019.

  • 7.

    Busso T, Benoit H, Bonnefoy R, Feasson L, Lacour J-R. Effects of training frequency on the dynamics of performance response to a single training bout. J Appl Physiol. 2002;92(2):572580. PubMed ID: 11796666 doi:10.1152/japplphysiol.00429.2001

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 8.

    Soligard T, Schwellnus M, Alonso J-M, et al. How much is too much? (Part 1) International Olympic Committee consensus statement on load in sport and risk of injury. Br J Sports Med. 2016;50(17):10301041. PubMed ID: 27535989 doi:10.1136/bjsports-2016-096581

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    • Search Google Scholar
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  • 9.

    Jeffries AC, Marcora SM, Coutts AJ, Wallace L, McCall A, Impellizzeri FM. Development of a revised conceptual framework of physical training for use in research and practice. Sports Med Auckl NZ. 2022;52(4):709724. doi:10.1007/s40279-021-01551-5

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 10.

    Staunton CA, Abt G, Weaving D, Wundersitz DWT. Misuse of the term ‘load’ in sport and exercise science. J Sci Med Sport. 2022;25(5):439444. https://www.sciencedirect.com/science/article/pii/S1440244021002127. Accessed September 30, 2021. PubMed ID: 34489176 doi:10.1016/j.jsams.2021.08.013

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 11.

    Wallace LK, Slattery KM, Impellizzeri FM, Coutts AJ. Establishing the criterion validity and reliability of common methods for quantifying training load. J Strength Cond Res. 2014;28(8):23302337. PubMed ID: 24662229 doi:10.1519/JSC.0000000000000416

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 12.

    Renfree A, Casado A, McLaren S. Re-thinking athlete training loads: would you rather have one big rock or lots of little rocks dropped on your foot? Res Sports Med. 2021 Mar 24:14. doi:10.1080/15438627.2021.1906672. Epub ahead of print. PMID: 33759653.

    • Search Google Scholar
    • Export Citation
  • 13.

    Burgomaster KA, Howarth KR, Phillips SM, et al. Similar metabolic adaptations during exercise after low volume sprint interval and traditional endurance training in humans. J Physiol. 2008;586(1):151160. PubMed ID: 17991697 doi:10.1113/jphysiol.2007.142109

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 14.

    Gibala MJ, Little JP, van Essen M, et al. Short-term sprint interval versus traditional endurance training: similar initial adaptations in human skeletal muscle and exercise performance. J Physiol. 2006;575(3):901911. PubMed ID: 16825308 doi:10.1113/jphysiol.2006.112094

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 15.

    Coakley SL, Passfield L. Individualised training at different intensities, in untrained participants, results in similar physiological and performance benefits. J Sports Sci. 2018;36(8):881888. PubMed ID: 28749254 doi:10.1080/02640414.2017.1346269

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 16.

    Kesisoglou A, Nicolò A, Passfield L. Cycling performance and training load: effects of intensity and duration. Int J Sports Physiol Perform. 2021;16(4):535543. PubMed ID: 33059328 doi:10.1123/ijspp.2020-0072

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 17.

    Nicolò A, Bazzucchi I, Haxhi J, Felici F, Sacchetti M. Comparing continuous and intermittent exercise: an “isoeffort” and “isotime” approach. PLoS One. 2014;9(4):e94990. PubMed ID: 24736313 doi:10.1371/journal.pone.0094990

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 18.

    Nicolò A, Massaroni C, Passfield L. Respiratory frequency during exercise: the neglected physiological measure. Front Physiol. 2017;8:922. PubMed ID: 29321742 doi:10.3389/fphys.2017.00922

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 19.

    van Erp T, Foster C, de Koning JJ. Relationship between various training-load measures in elite cyclists during training, road races, and time trials. Int J Sports Physiol Perform. 2019;14(4):493500. PubMed ID: 30300025 doi:10.1123/ijspp.2017-0722

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 20.

    Kesisoglou A, Nicolò A, Howland L, Passfield L. Continuous versus intermittent running: acute performance decrement and training load. Int J Sports Physiol Perform. 2021;16(12):17941803. PubMed ID: 34021094 doi:10.1123/ijspp.2020-0844

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    • Search Google Scholar
    • Export Citation

Passfield (louis.passfield@ucalgary.ca) is corresponding author.

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    Figure 1

    —A principles-of-training diagram showing how a training dose leads to an acute performance decrement (black circle). A low training dose is theorized to result in a smaller decrement and performance benefit compared with a larger training dose.

  • 1.

    McLaren SJ, Shushan T, Schneider C, Ward P. Comment on Passfield et al.: validity of the training-load concept. Int J Sports Physiol Perform. Published online July 2022. doi:10.1123/ijspp.2022-0147

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 2.

    Slattery KM, Wallace LK, Coutts AJ. Comment on Passfield et al: defending the use of oxygen uptake as a criterion measure for training load. Int J Sports Physiol Perform. Published online July 2022. doi:10.1123/ijspp.2022-0154

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 3.

    Passfield L, Murias JM, Sacchetti M, Nicolò A. Validity of the training-load concept. Int J Sports Physiol Perform. 2022;17(4):507514. PubMed ID: 35247874 doi:10.1123/ijspp.2021-0536

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 4.

    Banister EW, Calvert TW, Savage MV, Bach TM. A systems model of training for athletic performance. Aust J Sports Med. 1975;7:5761.

  • 5.

    Issurin VB. New horizons for the methodology and physiology of training periodization. Sports Med Auckl NZ. 2010;40(3):189206. doi:10.2165/11319770-000000000-00000

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 6.

    Bompa TO, Buzzichelli CA. Periodization: Theory and Methodology of Training. 6th ed. Human Kinetics; 2019.

  • 7.

    Busso T, Benoit H, Bonnefoy R, Feasson L, Lacour J-R. Effects of training frequency on the dynamics of performance response to a single training bout. J Appl Physiol. 2002;92(2):572580. PubMed ID: 11796666 doi:10.1152/japplphysiol.00429.2001

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 8.

    Soligard T, Schwellnus M, Alonso J-M, et al. How much is too much? (Part 1) International Olympic Committee consensus statement on load in sport and risk of injury. Br J Sports Med. 2016;50(17):10301041. PubMed ID: 27535989 doi:10.1136/bjsports-2016-096581

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 9.

    Jeffries AC, Marcora SM, Coutts AJ, Wallace L, McCall A, Impellizzeri FM. Development of a revised conceptual framework of physical training for use in research and practice. Sports Med Auckl NZ. 2022;52(4):709724. doi:10.1007/s40279-021-01551-5

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 10.

    Staunton CA, Abt G, Weaving D, Wundersitz DWT. Misuse of the term ‘load’ in sport and exercise science. J Sci Med Sport. 2022;25(5):439444. https://www.sciencedirect.com/science/article/pii/S1440244021002127. Accessed September 30, 2021. PubMed ID: 34489176 doi:10.1016/j.jsams.2021.08.013

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 11.

    Wallace LK, Slattery KM, Impellizzeri FM, Coutts AJ. Establishing the criterion validity and reliability of common methods for quantifying training load. J Strength Cond Res. 2014;28(8):23302337. PubMed ID: 24662229 doi:10.1519/JSC.0000000000000416

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 12.

    Renfree A, Casado A, McLaren S. Re-thinking athlete training loads: would you rather have one big rock or lots of little rocks dropped on your foot? Res Sports Med. 2021 Mar 24:14. doi:10.1080/15438627.2021.1906672. Epub ahead of print. PMID: 33759653.

    • Search Google Scholar
    • Export Citation
  • 13.

    Burgomaster KA, Howarth KR, Phillips SM, et al. Similar metabolic adaptations during exercise after low volume sprint interval and traditional endurance training in humans. J Physiol. 2008;586(1):151160. PubMed ID: 17991697 doi:10.1113/jphysiol.2007.142109

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 14.

    Gibala MJ, Little JP, van Essen M, et al. Short-term sprint interval versus traditional endurance training: similar initial adaptations in human skeletal muscle and exercise performance. J Physiol. 2006;575(3):901911. PubMed ID: 16825308 doi:10.1113/jphysiol.2006.112094

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 15.

    Coakley SL, Passfield L. Individualised training at different intensities, in untrained participants, results in similar physiological and performance benefits. J Sports Sci. 2018;36(8):881888. PubMed ID: 28749254 doi:10.1080/02640414.2017.1346269

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 16.

    Kesisoglou A, Nicolò A, Passfield L. Cycling performance and training load: effects of intensity and duration. Int J Sports Physiol Perform. 2021;16(4):535543. PubMed ID: 33059328 doi:10.1123/ijspp.2020-0072

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 17.

    Nicolò A, Bazzucchi I, Haxhi J, Felici F, Sacchetti M. Comparing continuous and intermittent exercise: an “isoeffort” and “isotime” approach. PLoS One. 2014;9(4):e94990. PubMed ID: 24736313 doi:10.1371/journal.pone.0094990

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 18.

    Nicolò A, Massaroni C, Passfield L. Respiratory frequency during exercise: the neglected physiological measure. Front Physiol. 2017;8:922. PubMed ID: 29321742 doi:10.3389/fphys.2017.00922

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 19.

    van Erp T, Foster C, de Koning JJ. Relationship between various training-load measures in elite cyclists during training, road races, and time trials. Int J Sports Physiol Perform. 2019;14(4):493500. PubMed ID: 30300025 doi:10.1123/ijspp.2017-0722

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 20.

    Kesisoglou A, Nicolò A, Howland L, Passfield L. Continuous versus intermittent running: acute performance decrement and training load. Int J Sports Physiol Perform. 2021;16(12):17941803. PubMed ID: 34021094 doi:10.1123/ijspp.2020-0844

    • Crossref
    • Search Google Scholar
    • Export Citation
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