Background

High-intensity training (HIT) programs are popularly associated with improvements in exercise efficiency and body composition though, at extremes, have been accompanied by concerns of secondary rhabdomyolysis and severe acute kidney injury (AKI). Beyond the anecdotal, robust literature on the physiological impact of HIT on renal function is currently limited.

Aims

To investigate the acute impact of high-intensity (CrossFit®) training on renal function, and to evaluate the incidence of AKI by Risk, Injury, Failure, Loss, End-stage renal disease (RIFLE) criteria following CrossFit® training.

Methods

Clinical and biochemical parameters were measured in 22 healthy adults before and after two CrossFit® workouts: ‘Fran’ (12 men, 10 women) and ‘Macho Man’ (9 men, 4 women).

Results

Serum creatinine increased by 16 ± 10 μmol/L following ‘Fran’ and 18 ± 12 μmol/L following ‘Macho Man’ (p < 0.05). Cystatin C did not change significantly following ‘Fran’ and increased by 0.06 ± 0.06 mg/L (p < 0.05) following ‘Macho Man’. AKI as defined by RIFLE ‘Risk’ criteria was observed in 5/22 participants (23%) following ‘Fran’ and 5/13 participants (38%) following ‘Macho Man’. Urinary albumin/creatinine ratio rose by 18.7 ± 18.3 and 5.2 ± 6.0 mg/mmol following ‘Fran’ and ‘Macho Man’ respectively off nonalbuminuric baselines (p < 0.05).

Conclusions

Intense (CrossFit®) exercise is associated with significant metabolic demands and alterations in parameters of renal physiology and function. The observed rise in both conventional and novel biomarkers of renal function following the workout ‘Macho Man’ specifically may indicate a degree of transient subclinical functional impairment with CrossFit®-type training.

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