Effect of ingesting carbohydrate only or carbohydrate plus casein protein hydrolysate during a multiday cycling race on left ventricular function, plasma volume expansion and cardiac biomarkers.

Purpose: Multiday racing causes mild left ventricular (LV) dysfunction from day 1 that persists on successive days. We evaluated ingesting casein protein hydrolysate-carbohydrate (PRO) compared with carbohydrate-only (CHO) during a 3-day mountain bike race.

Methods: Eighteen male cyclists were randomly assigned to ingest 6.7% carbohydrate without (CHO) or with 1.3% casein hydrolysate (PRO) during racing (~ 4-5 h/day; 68/71/71 km). Conventional LV echocardiography, plasma albumin content, plasma volume (PV) and blood biomarkers were measured before day 1 and post race on day 3.

Results: Fourteen cyclists (n = 7 per group) completed the race. PV increased in CHO (mean increase (95% CI), 10.2% (0.1 to 20.2)%, p = 0.045) but not in PRO (0.4% (- 6.1 to 6.9)%). Early diastolic transmitral blood flow (E) was unchanged but deceleration time from peak E increased post race (CHO: 46.7 (11.8 to 81.6) ms, p = 0.019; PRO: 24.2 (- 0.5 to 48.9) ms, p = 0.054), suggesting impaired LV relaxation. Tissue Doppler mitral annular velocity was unchanged in CHO, but in PRO septal early-to-late diastolic ratio decreased (p = 0.016) and was compensated by increased lateral early (p = 0.034) and late (p = 0.012) velocities. Systolic function was preserved in both groups; with increased systolic lateral wall velocity in PRO (p = 0.002). Effect size increase in serum creatine kinase (CK) activity, CK-MB and C-reactive protein concentrations was less in PRO than CHO (Cohen's d mean ± SD, PRO: 2.91 ± 2.07; CHO: 7.56 ± 4.81, p = 0.046).

Conclusion: Ingesting casein hydrolysate with carbohydrate during a 3-day race prevented secondary hypervolemia and failed to curb impaired LV relaxation despite reducing tissue damage and inflammatory biomarkers. Without PV expansion, systolic function was preserved by lateral wall compensating for septal wall dysfunction.