Table 6.

Summary of methods utilized or emerging to quantify athlete training load to monitor recovery and performance

Method	Used today in sports	Wearables utilized	Metrics	Advantages/disadvantages
Questionnaire	Yes	No	Verbal or written form	Advantage: Easy to conduct
				Disadvantage: Highly variable; often inaccurate
Session-rate of perceived exertion	Yes	No	Scale from 1 to 9 detailing intensity of workout. Scale used in conjunction with workout duration to determine load	Advantage: Easy to assess
				Disadvantage: Highly variable; often inaccurate
Blood lactate	Yes (emerging)	No	Concentration	Advantage: Used to predict anaerobic threshold (kicks in when exercise is increased and the aerobic system can no longer keep up with the body’s energy system
				Disadvantage: Cost, inefficient, time-varying process
Tri-axial accelerometers and GPS	Yes	Yes: Catapult, Zebra	Acceleration, location, and velocity used to compute PlayerLoad (arbitrary unit) to derive ACWR	Advantage: Easy to utilize
				Disadvantage: Variability in sensor technology could lead to inaccuracy. Need to develop algorithms to filter noise (e.g. player moving on the sideline compared to on-field performance)
Heart rate	No	Yes: Apple Watch, Fitbit, Polar	Time in HR zones, HRV	Advantage: Easy to collect large data sets for robust analysis
				Disadvantage: Variability in sensor technology could lead to inaccuracy. Sensor location attributed to deviations.
Muscle oxygen saturation	No	Yes: Humon Hex	SmO2 levels stratified into workout zones	Advantage: Easy to collect large data sets
				Disadvantage: Need for validation of models
Biochemical concentration5–8	No	No devices used to monitor training load and recovery directly. Indirect measures include monitoring hydration levels and sweat rate	Concentration	Advantage: Insight into the biochemistry of the athlete to predict hypohydration, hyponatremia, and fatigue.
				Disadvantage: Technology still developing. Need to develop predictive analytics based on the biochemical profile of the athlete