Changes in Selected Blood Measures During Repeated Days of Intense Training and Carbohydrate Control

Abstract

Ten runners were studied to determine whether selected blood measures were useful indices of the metabolic stress associated with intense training and dietary carbohydrate (CHO) deficiency. The runners performed two diet/training regimens, involving 5 repeated days of intense training ∼80 min/d, ∼80% V̇O₂max) and dietary CHO control (8.0 g·kg^-1·d^-1 EQ-CHO; 3.9 g·kg^-1·d^-1, LO-CHO). Resting blood samples were obtained after a 3-day control period, after 3 and 5 days of intense training, and after 3 days of rest. Resting uric acid levels were significantly higher (P < 0.05) after 3 and 5 days of training during the LO-CHO vs EQ-CHO regimen (353±21 vs 309±24, and 345±26 vs 302±26 mol·l^-1, respectively). Resting thyroxine (T₄) levels were higher (P < 0.05) after 5 days of training during the LO-CHO vs EQ-CHO regimen (102.2±6.2 vs 83.7±4.5 nmol·l^-1, respectively). While creatine kinase levels were elevated after both regimens (P < 0.05), there was no difference between regimens. Serum Cortisol (C) levels were reduced by 10% for both regimens (P < 0.05), possibly due to an expansion in plasma volume (7.6 and 7.3% for the LO-CHO and EQ-CHO regimens, respectively). Resting FFA levels were increased (P < 0.05) during both regimens, but there was no difference between the regimens. Neither exercise/diet regimen had any significant effect on total testosterone (T), the T/C molar ratio, or plasma glucose. It was concluded that elevated uric acid levels appear to reflect the increased metabolic strain imposed by diminishing muscle glycogen stores, and may be a useful indicator of training overload when athletes fail to match CHO intake to expenditure.

Key words

Exercise - uric acid - creatine kinase - thyroxine - Cortisol - testosterone - glucose - free fatty acids - glycerol - lactate