Muscle Damage, Soreness, and Stress During Preseason Training in Collegiate Swimmers.

BACKGROUND: In 2014, 6 collegiate swimmers were hospitalized for symptomatic exertional rhabdomyolysis. OBJECTIVE: To serially monitor and assess relationships between skeletal muscle membrane disruption, upper body soreness (UBS) and lower body soreness (LBS), and stress during the first 6 weeks (timepoints) of preseason training in collegiate male and female swimmers. DESIGN: Prospective observational study. SETTING: College/university. PARTICIPANTS: Forty swimmers. INDEPENDENT VARIABLES: Upper and lower body soreness rating (0-10); testosterone (T), cortisol (C), and T/C ratio. MAIN OUTCOME MEASURES: Creatine kinase (CK) and myoglobin (over time) versus independent variables. RESULTS: Weekly training load consisted of ∼87% swimming, ∼5% running, and ∼8% weight training, which increased from 15.8 hours to 20.5 total training hours per week over the first 6 weeks of training. Muscle damage in collegiate swimmers was modest and peaked after the first week of training (week 2) for men (CK = 438 ± 259 U/L; P < 0.0001; r2 = 0.28; myoglobin = 47 ± 18 ng/mL; P = 0.001; r2 = 0.22) and women (CK = 446 ± 723 U/L; P < 0.01; r2 = 0.13; myoglobin = 63 ± 140 ng/mL, not significant) with high variability. Data were presented as peak mean ± SD, significant P value, and r2 from repeated-measures analysis of variance. A temporal disconnect was noted between muscle damage and UBS, which peaked at week 5 in both men (5 ± 2; P < 0.0001; r2 = 0.44) and women (6 ± 2; P < 0.0001; r2 = 0.57). The serum cortisol level decreased over time, which peaked at week 1 (baseline) in men (15 ± 6 µg/dL; P = 0.0004; r2 = 0.38) and women (19 ± 10 µg/dL; P < 0.0001; r2 = 0.49). The testosterone level remained unchanged, which promoted an anabolic hormonal environment that peaked at week 6 (increasing T/C ratio) in men (58 ± 32; P = 0.0003; r2 = 0.31) and women (4 ± 3; P = 0.04; r2 = 0.18) despite gradual increases in training and soreness. CONCLUSIONS: Muscle soreness does not parallel muscle membrane disruption. A 1-week "transition" period is required for muscles to adapt to intense/novel training.