Understanding Training Load
The stress-response mechanism behind every coaching decision: dose-response theory, progressive overload, detraining, functional overreaching, and the four-step training load process.
Source: PhD Thesis, Chapter 2 · §2.1–§2.2 · Deakin University Repository →
This page is adapted from the Literature Review of Leighton Wells' doctoral thesis: Triathlon Coaching Practices — Optimising Training Load Processes and Communication. Read the full thesis →
Cardiovascular adaptations to physical training
DOI →Monitoring athlete training loads: Consensus statement
DOI →Internal and external training load: 15 years on
DOI →Training and competition readiness in triathlon
DOI →Measuring psychological load in sport
DOI →Recovery and performance in sport: consensus statement
DOI →Triathlon, coaching, and the training load challenge
Triathlon began in San Diego around 1974.1 The Ironman — 3.8 km swim, 180 km bike, 42.2 km run — started in Hawaii in 1978,2 and the sport became Olympic in 2000 at the Standard Distance.3 In the decades since, training methods and technologies have evolved significantly: the first wireless heart rate monitor arrived in 1981,4 the first cycling power meter in 1986.5
Coaches and athletes now have access to rich data from sports watches,8 digital-virtual training environments,9 and training management systems (TMS) that enable the prescription, measurement, monitoring and management of training.11 Triathlon is a major global sport — over three million participants compete annually in the United States alone,12 with 115,000 participants, 600 coaches, and more than 200 registered squads and clubs in Australia in 2021/22.13
Race performance has improved across professional and age-group athletes over recent decades,14 with technological developments in aerodynamic bikes,15 helmets,16 and wetsuit materials17 contributing. But while there is uncertainty about ideal training volume and intensity,2,22,23 it remains unclear whether improved coaching practices have also occurred. Almost nothing is known about the practices of triathlon coaches, especially concerning load prescription and management.
There are established methods of load prescription, measurement, monitoring and management from Foster,27 Borg,28 Banister,29 and Bompa.30 Consensus statements provide general guidelines,32,33 but no reports indicate how closely triathlon coaches adhere to them.
The gap is stark: triathlon is one of the largest participation sports globally, with a high proportion of athletes being coached, yet the evidence base for how those coaches actually manage training load is almost entirely absent. This Knowledge Hub exists, in part, because that gap needed to be articulated and addressed.
The stress-response mechanism
The purpose of applying training load is to exploit the body's stress-response mechanism.39 This mechanism represents responses to the exercise or 'work' the athlete performs: an in-session response,40 an immediate post-session response,41 and the potential for short-, medium-, and long-term physiological adaptations.
Long-term adaptations include increased mitochondrial density42 and increased cross-sectional area of muscle,43 both of which aid performance.44 But these adaptations can only occur optimally under two conditions: by avoiding extended periods of overload, and ensuring the athlete's body is sufficiently recovered.45
A notable example of sub-optimal recovery occurs when a resistance training session is performed too close to an endurance session — the potential physiological adaptations of both are 'blunted'.46 The body rebuilds, repairs, and remodels during recovery periods, which is when physiological adaptation occurs.47 This process is also termed regeneration.48
Progressive overload — a gradual increase in training load — is a core concept of load prescription.49 But the balance is difficult: detraining (performance loss from insufficient stimulus50) sits at one end, and overreaching (performance loss from exceeding the athlete's capacity) at the other.
This is the foundational tension every coach manages daily: enough load to drive adaptation, enough recovery to let it happen, without crossing into the territory where the athlete breaks down. The fact that concurrent training (strength + endurance) can blunt adaptations has direct implications for how triathlon training is scheduled.
What training load actually means
Traditionally, training load is the total amount of physical stimulus an athlete is exposed to over a given timeframe.51,52 In this thesis, it is defined as the product of duration (session length) and intensity (level of effort applied),65,66 though other definitions exist — including training load as "the cumulative amount of stress placed on an individual from single or multiple training sessions over a period of time".67
Load is a complex landscape of internal and external factors, objective and subjective measures, and sporting and non-sporting stressors that the coach must carefully balance. It is essential to prescribe load carefully to progress physiological capacity while avoiding illness and injury from too much training or insufficient rest.32,53
The athlete begins at a baseline fitness 'floor', established via testing.54 They train within their individual load 'floor' and 'ceiling', aiming to 'peak' for competition.55 Non-functional overreaching (NFOR)56 and overtraining syndrome (OTS)57,58 represent the risk of accumulating too great a load over extended periods.
Critically, balancing load is not just about physiological stress. Overloading the athlete's mental capacity — combining sport load with self-directed non-sport tasks — can decrease motivation, impact mood,31 reduce attention during sessions,59 and ultimately result in burnout60 and documented mental health disorders.61
A critique by Impellizzeri et al.68 argues that training load should be viewed as an exposure-response mechanism analogous to pharmacological interventions — incorrectly prescribed training can have detrimental health consequences. Contested
The four-step training load process
The thesis structures the training load process around four steps. This does not represent the only or best way to conceptualise this — some practitioners may consider measurement and monitoring to be the same, or combine monitoring and management. But it provides a useful organising structure:
Prescribe Load
Design the optimal prescription of load in the training program. Make careful choices about which load metrics to use.
Measure Load
Using measures of External Load and/or Internal Load (objective and subjective). May also include life load and Internal Load Response variables.
Monitor Load
Compare prescribed and actual load (adherence). Identify changes in the relationship between external and internal load. Determine whether response values indicate sub-optimal load.
Manage Load
Based on monitoring interpretations, make decisions about adjustments to prescribed load. Include consideration of life load, functional overreaching, and proximity to competition.
This four-step framework — prescribe, measure, monitor, manage — is the structural backbone of the entire thesis. Every subsequent Knowledge Hub page connects back to one or more of these steps. The framework is discussed further in Chapter 3.1 of the thesis and operationalised across all three thesis studies.
The coach should recognise that the non-sporting part of the athlete's life also creates physiological and psychological stress — load — which influences training and adaptation.31 The literature refers to sport load and non-sport load combined as 'life load'.31
→ Read more: Life Load — Why Training Stress Is Only Half the Picture
"Load is a complex landscape of internal and external factors, objective and subjective measures, and sporting and non-sporting stressors that the coach must carefully balance."
— Wells, 2024. Triathlon Coaching Practices, §2.2
Key takeaways
Training load drives adaptation — and risk
The stress-response mechanism is the foundation. Load must be sufficient to drive adaptation but managed to prevent overreaching, illness, and burnout.
Load is more than physical stimulus
Mental load, non-sport stressors, and the athlete's broader life context all contribute to total load. Ignoring these creates blind spots in load management.
The coaching evidence gap is significant
Despite triathlon's scale, almost nothing was known about how coaches actually prescribe and manage training load — a gap this thesis directly addresses.
This page draws on the Literature Review of Leighton Wells' doctoral thesis and the work of the researchers cited below, whose contributions have shaped the fields of training load science, coaching practice, recovery, and triathlon research.
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- 2Triathlon Injuries: Transitioning from Prevalence to Prediction and Prevention. Current Sports Medicine Reports. 2017;16(6):397–403. ↩
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- 5The influence of exercise intensity on the association between kilojoules spent and various training loads. IJSPP. 2019;14(10):1395–400. ↩
- 8Accuracy of distance recordings in eight positioning-enabled sport watches. JMIR Mhealth Uhealth. 2020;8(6):1–11. ↩
- 11
- 27Monitoring training in athletes with reference to overtraining syndrome. Med Sci Sports Exerc. 1998;30(7):1164–8. ↩
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- 29A Systems Model of the Effects of Training on Physical Performance. IEEE Trans Syst Man Cybern. 1976;SMC-6(2):94–102. ↩
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- 41Acute and post-exercise physiological responses to high-intensity interval training. J Sports Sci Med. 2017;16(2):219. ↩
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- 43Effects of combined resistance and cardiovascular training on strength, power, muscle cross-sectional area, and endurance markers. Eur J Appl Physiol. 2005;94(1):70–5. ↩
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- 46Development of maximal dynamic strength during concurrent resistance and endurance training. Sports Medicine. 2021;51(5):991–1010. ↩
- 48
- 49Monitoring changes in performance, physiology, biochemistry, and psychology during overreaching and recovery in triathletes. IJSM. 2007;28(02):125–34. ↩
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- 56Prevention, diagnosis, and treatment of the overtraining syndrome. Med Sci Sports Exerc. 2013;45(1):186–205. ↩
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- 65New horizons for the methodology and physiology of training periodization. Sports Medicine. 2010;40(3):189–206. ↩
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