title: Interpreting daily heart rate variability changes in collegiate female soccer players.
abstract: BACKGROUND
  Heart rate variability (HRV) is an objective physiological marker that may be useful for monitoring training status in athletes. However, research aiming to interpret daily HRV changes in female athletes is limited. The objectives of this study were: 1) to assess daily HRV (i.e., log-transformed root mean square of successive R-R interval differences, lnRMSSD) trends both as a team and intra-individually in response to varying training load (TL); and 2) to determine relationships between lnRMSSD fluctuation (coefficient of variation, lnRMSSDcv) and psychometric and fitness parameters in collegiate female soccer players (N.=10).
  
  
  METHODS
  Ultra-short, Smartphone-derived lnRMSSD and psychometrics were evaluated daily throughout 2 consecutive weeks of high and low TL. After the training period, fitness parameters were assessed.
  
  
  RESULTS
  When compared to baseline, reductions in lnRMSSD ranged from unclear to very likely moderate during the high TL week (effect size ±90% confidence limits [ES±90% CL] =-0.21±0.74 to -0.64±0.78, respectively) while lnRMSSD reductions were unclear during the low TL week (ES±90% CL=-0.03±0.73 to -0.35±0.75, respectively). A large difference in TL between weeks was observed (ES±90% CL=1.37±0.80). Higher lnRMSSDcv was associated with greater perceived fatigue and lower fitness (r [upper and lower 90% CL]=-0.55 [-0.84, -0.003] large, -0.65 [-0.89, -0.15] large).
  
  
  CONCLUSIONS
  Athletes with lower fitness or higher perceived fatigue demonstrated greater reductions in lnRMSSD throughout training. This information can be useful when interpreting individual lnRMSSD responses throughout training for managing player fatigue.
authors.affiliation: Department of Kinesiology, Exercise Physiology Laboratory, University of Alabama, Tuscaloosa, AL, USA - aflatt@crimson.ua.edu.|Human Performance Laboratory, Auburn University at Montgomery, Montgomery, AL, USA - aflatt@crimson.ua.edu.
authors.forename: Andrew A
authors.initials: AA
authors.lastname: Flatt
authors.affiliation: Department of Kinesiology, Exercise Physiology Laboratory, University of Alabama, Tuscaloosa, AL, USA.|Human Performance Laboratory, Auburn University at Montgomery, Montgomery, AL, USA.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Esco
authors.affiliation: Department of Physical Education, State University of Londrina, Londrina, Brazil.
authors.forename: Fabio Y
authors.initials: FY
authors.lastname: Nakamura
authors.affiliation: High Performance Sport New Zealand, Auckland, New Zealand.|Department of Sport and Recreation, Waikato University, Hamilton, New Zealand.|Sports Performance Research Institute New Zealand (SPRINZ), Auckland University of Technology, Auckland, New Zealand.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Plews
mesh_terms: D015444:Exercise / Q000502:physiology*; D005221:Fatigue / Q000523:psychology; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D010465:Perception; D005082:Physical Exertion / Q000502:physiology*; D010809:Physical Fitness / Q000502:physiology*; D012916:Soccer / Q000502:physiology*; D011795:Surveys and Questionnaires; D055815:Young Adult