Author(s): VENCKUNAS, T., MINDERIS, P., SILINSKAS, V., BULIUOLIS, A., MAUGHAN, R.J., KAMANDULIS, S., Institution: LITHUANIAN SPORTS UNIVERSITY, Country: LITHUANIA, Abstract-ID: 1979

INTRODUCTION:
Carbohydrate (CHO) metabolism is crucial for performance in middle distance races. However, it has so far not been studied robustly if low glycogen stores could interfere with the exercise capacity in the field conditions of relatively short endurance events. It thus remains to be determined if diminished glycogen stores affect sports performance where relatively small amounts of CHO are required to complete the race. The present study tested how 1500 m race is affected by dietary manipulation intended to alter pre-race glycogen reserves in high-level runners.
METHODS:
National level middle distance runners [n=11 (4 females); age: 21.4 (SD 4.3) y, height: 179.5 (10.5) cm, BMI: 21.2 (1.5), training volume: 12.3 (1.8) h/wk, 69 (25) km/wk] completed, in a randomized cross-over design, a 1500 m time trial (TT) after abundant (High) or restricted (Low) CHO consumption for 2 days after glycogen depleting session (60 min of continuous moderate intensity run followed by 10 x 200 m at planned 1500 m TT pace).
CHO intake during 5 days before the each glycogen depleting session averaged 4.8 (1.4) g/kg/d. To keep the diet between glycogen depleting session and TT eucaloric, the Low condition required substitution of most of the diet CHO with fats, while the High condition required consumption of foods high in CHO and low in fats (protein intake was aimed to be unchanged). During Low and High conditions, CHO intake was <2 g/kg/d (average 1.0 (0.4) g/kg/d) and >5 g/kg/d (average 9.7 (2.6) g/kg/d), respectively. The TT took place in an indoor 200 m track and was run individually with time recorded every 100 m split. Striding pattern, heart rate (HR), capillary blood lactate and glucose dynamics and plasma malondialdehyde (MDA, an oxidative stress marker) response were determined.
RESULTS:
Time to complete 1500 m TT was slower in Low vs. High condition by 4.5 (4.5) s (i.e. by ~2%; p<0.01). Slowing in the later stages of the race in Low condition was largely due to decrease in stride length (p<0.05) rather than stride frequency. HR response to TT was not affected by feeding condition. Blood lactate and glucose were lower immediately before TT in Low vs. High condition (1.8 (0.5) vs. 2.2 (0.7) mmol/l and 5.4 (0.7) vs. (5.9 (0.8) mmol/l, p=0.022 and 0.007, respectively), peak lactate was higher in High vs. Low condition (16.8 (3.1) vs. 14.5 (4.2) mmol/l, p=0.039), while glucose was not affected by feeding condition during the 15 min of passive recovery. Plasma MDA levels did not differ between the conditions before TT, and 15 min after TT increased similarly by 15 % in Low (p=0.03) and High (p<0.01) conditions.
CONCLUSION:
In conclusion, compared to CHO restriction, a diet with ample CHO after a glycogen depleting session allowed for faster 1500 m race in high-level distance runners. Restriction of CHO to <2 g/kg/d after the glycogen exhaustion session slightly reduced baseline and peak blood lactate values but did not markedly change blood glucose or plasma MDA response to 1500 m race.