REF-406 · Lundstrom EA, De Souza MJ, Koltun KJ, Strock NCA, Canil HN & Williams NI, 2024 · International Journal of Sports Science and Coaching, · Paper
Wearable technology metrics are associated with energy deficiency and psychological stress in elite swimmers
Participants
n=23 NCAA swimmers (10 male, 13 female) during heavy training
Protocol
Wearable-derived HRV, resting heart rate (RHR), exercise strain and recovery
Lab-based metabolism: resting metabolic rate (RMR) and total triiodothyronine (TT3)
Psychological stress: RESTQ-52 (Recovery-Stress Questionnaire for Athletes)
Swimmers grouped by degree of metabolic adaptation to energy deficiency using the actual-to-predicted RMR ratio (validated cutoff <0.94) and by sex
Key Results
Metabolically suppressed swimmers had lower HRV (81 ± 27 ms vs 110 ± 35 ms, p=0.04)
HRV correlated positively with RMR per kg lean body mass (r=0.45, p=0.03)
HRV correlated negatively with sport-specific stress (r=−0.46, p=0.03) and total stress (r=−0.46, p=0.03)
In males only: HRV correlated negatively with general stress (r=−0.72) and total stress (r=−0.74); wearable strain correlated positively with recovery-stress balance (r=0.69) and negatively with general stress (r=−0.81) and sport stress (r=−0.89)
In females, no correlations between HRV, RHR, strain or recovery and any stress variable
Mechanism
Inference, not tested: lower HRV in metabolically suppressed swimmers is consistent with autonomic changes under low energy availability, and HRV tracking psychological stress fits the autonomic-stress literature. The study is correlational and does not show that wearable data causes stress or that a feedback loop exists.
Practical Application
In 23 NCAA swimmers in heavy training, those with a suppressed metabolism (actual/predicted RMR <0.94, a marker of energy deficiency) had lower wearable HRV (81 vs 110 ms), and HRV tracked both RMR and questionnaire stress; in females none of the wearable metrics correlated with stress — wearable HRV carries a real signal about energy deficiency and stress, but the associations are modest and sex-dependent
Low wearable HRV in a heavy block is a reason to check energy intake and stress, not a diagnosis — the study shows associations, not detection ahead of symptoms
Not from this paper; the base's own practice: a coach or sport scientist reviews the data and communicates selectively rather than the athlete self-monitoring daily
Not from this paper; the base's own practice: read HRV as a multi-week trend rather than a daily score REF-397
Sex matters: the wearable-stress associations here were driven by the males; do not assume the same read-out for female athletes
Limitations
Small sample (n=23), fewer still per sex subgroup
Cross-sectional — cannot determine causality
NCAA swimmers — may not generalize to amateur endurance athletes
Single heavy training period
How this entry was checked and changed
Why this level
regraded 2026-09-27 from B+: cross-sectional correlational study, n=23
Content correction 2026-09-27
"Bidirectional relationship: wearable data detects problems AND creates stress about those problems" -> not in the abstract (purely correlational study); removed as a finding, mechanism relabelled as inference.
"Athletes with lower recovery scores reported higher psychological stress" -> the abstract reports HRV-stress correlations (and strain-stress in males only), none in females; rewritten with the abstract's r values.
Level B+ -> B (cross-sectional, n=23); Tier "mixed→Tier 4-5" -> Tier 3 (NCAA swimmers).
"30-day trend is diagnostic" and coach-reviews-data advice -> labelled as the base's own practice.