The Australian team analyzed past studies to see how objective measures like muscle function and blood proteins responded to rises and drops in athletes' training load or to chronic heavy training. They also looked at how athletes' psychological stress levels and overall mood tracked with training load.
Subjective sense of wellbeing followed training load more closely than physiological measures, making it an important factor to monitor, researchers say.
Subjective measures are already widely used to monitor athlete response to training, said lead author Anna E. Saw of the School of Exercise and Nutrition Sciences at Deakin University in Burwood, Victoria.
"Training imposes a stress on the athlete, to which they can either respond positively and increase their performance capacity, or respond negatively with reduced performance capacity," Saw said.
"A negative response to training may also result in an athlete experiencing overtraining syndrome, athlete burnout, injury, or illness, potentially compromising their season or even their athletic career," she told Reuters Health by email.
The researchers reviewed 54 studies that included objective and subjective measures of athlete wellbeing during times of brief, intense training and of chronic intense training.
The studies compared measures like blood work and heart rate response to an athlete's reported mood, perceived stress, anxiety or other personal measures.
The researchers found that subjective measures were more sensitive and consistent in 22 of the 54 studies - athletes consistently reported a dip in wellbeing during acute training loads or a chronic training load, while an acute decrease in training load improved wellbeing.
There was some evidence that reduced training load was associated with better maximal oxygen consumption, but in general objective measures were not strongly tied to athlete wellbeing, the study team reports in the British Journal of Sports Medicine.
"Subjective measures provide insight into how an athlete perceives their physical and psychosocial wellbeing," Saw said.
Subjective measures are relatively simple and inexpensive to collect compared to objective measures, and they provide more meaningful information on how well the athlete is responding to training, she said.
Generally, subjective measures of wellbeing were not associated with performance, so athletes with objectively better performance could also have subjectively better wellbeing, she said.
"Wellbeing allows athletes to flourish in both sport and life outside of sport," Saw said. "Hence it is important that wellbeing is supported so that an athlete may achieve optimal performance, and also sporting longevity."
Subjective measures may detect a negative response to training early on, allowing for training modification, which may potentially mitigate the risk of injury, she said.
"The findings of the review serve to justify the use of subjective measures across any sport and participation level," Saw said. "This may lend to more emphasis and resources being directed towards subjective measures."
They may also improve the "buy-in" of athletes and staff, which is integral to effective implementation, she said.