Training quantification is basic to evaluate an endurance athlete's responses to training loads, ensure adequate stress/recovery balance, and determine the relationship between training and performance. Quantifying both external and internal workload is important, because external workload does not measure the biological stress imposed by the exercise sessions. Generally used quantification methods include retrospective questionnaires, diaries, direct observation, and physiological monitoring, often based on the measurement of oxygen uptake, heart rate, and blood lactate concentration. Other methods in use in endurance sports include speed measurement and the measurement of power output, made possible by recent technological advances such as power meters in cycling and triathlon. Among subjective methods of quantification, rating of perceived exertion stands out because of its wide use. Concurrent assessments of the various quantification methods allow researchers and practitioners to evaluate stress/ recovery balance, adjust individual training programs, and determine the relationships between external load, internal load, and athletes' performance. This brief review summarizes the most relevant external-and internal-workload-quantification methods in endurance sports and provides practical examples of their implementation to adjust the training programs of elite athletes in accordance with their individualized stress/recovery balance.
Keywords: external load, internal load, intensity, monitoring, training adaptationTraining is a process whereby athletes are exposed to systematic and repetitive exercise stimuli with the goal of inducing adaptations matched to a desirable function, such as delaying the onset of fatigue, increasing power output, refining motor coordination, or reducing the risk of injury. Coaches and trainers generally consider that the outcome of the training process depends on the type and amount of the stimulus, and understanding this cause-and-effect relationship between training dose and response is crucial to prescribe exercise training accordingly. 1 Nevertheless, to analyze and establish causal relationships between the training performed and the resultant physiological and performance adaptations, accurate and reliable quantification of the training load undertaken by the athlete is a sine qua non. It is simply not possible to identify the effects of training without a precise quantification of the training load. 2 This is the reason why several sport-science experts have previously underlined the importance of proper training quantification. For instance, Pollock 3 highlighted that many investigators reported their results without quantifying their training procedures, and with no mention of energy cost, heartrate intensity, miles covered, and so on. Along the same lines, Hopkins 4 indicated that with the links between training and outcomes such as performance and injury being so strong, it is surprising that the methodology of measurement of training has not been a focus of attention i...