## 2 External Load Monitoring
### Time-Motion Analysis
#### 2.1.1 Pedometers and Accelerometers  
Pedometers are simple instruments used to measure the steps taken by individuals during exercise, such as walking or running [15]. These devices are programmed to detect vertical movement of the hip, providing an approximate estimate of the horizontal distance covered during exercise [16]. Although pedometer use in monitoring the total number of steps during physical activity has been correlated with other devices, such as accelerometers (i.e., r = 0.86), the high mean difference in steps measured by these devices (accelerometers > pedometers) suggests a poor convergent validity of the pedometer [17]. However, the high correlation between pedometer and accelerometer regarding the counts of steps per a given unit of time suggests that pedometers can be considered a feasible method for providing individual feedback on time spent at different categories of step intensities (light, moderate, and vigorous), as were estimated using an accelerometer [17]. It is important to note that the pedometer only registers steps when the body moves vertically; therefore, pedometers cannot independently discriminate intensity levels during the movement, exercise mode, duration, distance, physical activity level, or the tolerance. However, when combined with other devices (e.g., stopwatch, pace tracker, accelerometer, and GPS) or additional information (e.g., age, body composition, height, weight, RPE, heart rate, and oxygen uptake), pedometers can estimate these variables with reasonable accuracy [7; 14; 18]. For example, the amount of steps per day determined with a pedometer correlates positively with conditioning tests (e.g., 6 min walk, r = 0.69), exercise tolerance (e.g., time in treadmill test, r = 0.41) and cardiorespiratory function (peak VO2, r = 0.22), and negatively with index of obesity (body mass index, r = -0.27) and aging (e.g., age, r = -0.21) [18]. Although pedometers are simpler instruments compared to devices such as accelerometers or GPS, an important application as a step counter device is the monitoring of the quantity of movement to achieve a recommended level of daily physical activity [15; 17]. Despite the low accuracy in measuring steps during walking and running, pedometers should not be dismissed as a tool for monitoring light to moderate aerobic activity, especially when other methods are unavailable. In such cases, pedometers can help individuals without training supervision to follow the World Health Organization 2020 guidelines on physical activity [19]. Consequently, because of the aforementioned limitations and the possibility of applying pedometers in controlling exercise for health purposes, it may be better recommended for training to enhance conditioning levels for a healthy lifestyle than athletic performance. On the other hand, accelerometers offer a greater range of information compared to pedometers [14; 16; 20]. For more than two decades, this instrument has been used in performance and fitness training programs [11; 12]. The accelerometer provides a wide range of data that facilitate monitoring external load, including distance covered, session duration, intensity times within the training session, HR, energy expenditure, sleep duration and quality, body temperature, and more [16; 20]. Moreover, monitoring step frequency with accelerometers presented high correlations with measurements of running velocity (r2 = 0.80), and when taking into account the effect of leg length and mass on the step frequency and displacement, the energy expenditure can be estimated accurately during walking (r2 = 0.84) and running (r2 = 0.86) [21]. Thus, accelerometers are considered suitable tools for controlling training load and adjusting planning according to individual goals, since data from external (distance, speed, and power) and internal (estimating energy demand) loads can be assessed and combined to enhance the analysis of training effects on health and performance [16; 20].