Fatigue & the Female Athlete: Part 3
Welcome back! In Part 1 of Fatigue and the Female Athlete, we explored the rapid growth of women’s sport and outlined key physiological differences between female and male athletes.
In Part 2, we learned fatigue among female athletes is poorly defined, with only a few studies providing explicit definitions. Generally, fatigue is characterized as a reversible decrease in physical and cognitive performance due to various physiological, neuromuscular, metabolic, and psychological stressors, compounded by sex-specific factors like hormonal fluctuations and energy levels. Similar to fatigue definitions, athlete-reported measures of fatigue vary significantly. Common athlete-reported outcome measures include Rating of Perceived Exertion (RPE), Hooper Index and the Recovery-Stress Questionnaire for Athletes (RESTQ-Sport), amongst others.
Objective Measures of Fatigue
Objective measures of fatigue can be assessed independently of the athlete's subjective reports. Below are some common objective measures:
Physiological Biomarkers:
Blood Lactate Levels: Elevated levels indicate increased anaerobic metabolism and can signify fatigue during exercise.
Cortisol Levels: This stress hormone can indicate overall fatigue and recovery status.
Creatine Kinase (CK): Elevated CK levels can reflect muscle damage.
Neuromuscular Performance:
Force Output: Measurement of peak force output through techniques like isometric strength testing.
Electromyography (EMG): Assesses muscle activation and fatigue levels by measuring electrical activity of specific muscles.
Heart Rate Monitoring:
Heart Rate Variability (HRV): Variation in time intervals between heartbeats may indicate fatigue and recovery status. There is some data to suggest low HRV correlates with increased fatigue.
Resting Heart Rate: Increases in resting heart rate may indicate fatigue, insufficient recovery or deconditioning.
Performance Metrics:
Time Trials, Repeated-Sprint Tests, Maximum Velocity Testing and other game or practice-based metrics that can be serially tracked.
Jump Performance Tests: Vertical jump tests and countermovement jumps are commonly used to assess lower-body power and fatigue.
Training Load Monitoring:
Session Rating of Perceived Exertion (sRPE): A quantitative reflection of training intensity measured through a standard formula to calculate training load.
Sleep Monitoring:
Actigraphy: Wearable devices that track sleep patterns can provide insights into quality and quantity of sleep, which relate to fatigue levels.
Polysomnography: Comprehensive sleep studies that evaluate sleep stages and disturbances.
Functional Movement Assessments:
Balance Tests and Agility Tests: Assess deterioration in motor skills and coordination, indicating fatigue.
By integrating these objective measures with subjective assessments, practitioners can gain a more complete understanding of an athlete's fatigue state and potential recovery needs.
Real-World Example
Meet Samantha, a 20 year old collegiate soccer player and biology major. During an in-season week, Samantha practices with her team three days, has two games (she is a high minute player >70 minutes per game)- usually one at her home stadium and one away which can include plane flights. She lifts two times per week and has one full rest/recovery day.
Let’s see how subjective and objective measures of fatigue are utilized throughout her week
Daily
Every morning at 9am she completes a daily wellness questionnaire rating her sleep duration and perceived sleep quality, muscle soreness, fatigue and mood on a 1-7 scale. She is also asked whether she is currently menstruating or not. Subjective: Hooper Index. Menstrual status. The results of these screenings can trigger further conversation and assessment.
Samantha wears a watch throughout the day and while she’s sleeping. She takes it off during practice. Objective: sleep hours and quality
Practice or game days
After each session (training and game), Samantha submits a rate of perceived exertion (RPE) rating.
Samantha wears a GPS unit during practice and games. Objective: amount and intensity of distance run, acels/decels, change of direction, maximal velocity
One time per week
Samanatha completes a heart rate recovery run at the beginning of the re-entry session. Objective: heart rate recovery
Samantha completes a single leg quiet stance test.
Samanatha completes a countermovement jump and seated knee extension isometric test. Objective: jump performance testing- reactive strength index and maximal force output
Samanatha’s sports medicine team reviews this information to inform short term and long term intervention strategies. A battery of tests is critical to capture the different fatigue domains (CNS fatigue, neuromuscular fatigue, metabolic fatigue, psychological fatigue), which require different intervention strategies. Outside of large fluctuations, these tests may be best used to identify trends over time and help identify a season-long “profile” of each individual.