The Effect Of Acute Carbohydrate Restriction On Squat Performance And Serum Energy Substrate Levels

Abstract

Carbohydrate restrictive diets have become increasingly prevalent among recreational and professional athletes as a means of losing weight and improving body composition. Currently, few data indicate a clear relationship between carbohydrate restriction (CR) and performance in resistance exercise (RE). PURPOSE: To investigate the acute effects of CR on squat performance and serum energy substrate levels in recreationally trained individuals. METHODS: Seven healthy recreationally trained males (22.6 + 3.47 yrs., 80.74 + 8.40 kg, 178.05 + 5.00 cm) completed RE under two conditions in randomized order: 1) control (CON) and 2) a (CR) condition, which included a carbohydrate depletion exercise trial (CDEX). In CR, subjects first performed the CDEX, which consisted of 60 minutes of cycling at >75% of participants’ heart rate (HR) max followed by four 1-minute bouts at >95% HR max with two minute rest in between sets. CDEX was then followed by 48 hours of reduced carbohydrate (CHO) intake (<5% daily caloric intake). RE in both CON and CR consisted of squats, loaded via inertial resistance using a Yo-YoTM flywheel squat device. Fasting blood glucose and triglyceride (TG) levels were measured pre-exercise in both conditions as well as throughout the CDEX. RESULTS: Total caloric intake was significantly (p < 0.001) lower during CR (mean + SD: 1661.24 + 691.6 kcal) compared to the CON (2433.85 + 527.4 kcal). No differences were found in total grams of protein (PRO) or fat intake between conditions. Percent total daily caloric intake from CHO (p < 0.001) was significantly lower in the CR condition (7.40 + 3.32% CHO), while percent total daily caloric intake from PRO and fat were significantly higher in the CR (32.90 + 8.54% PRO, 58.17 + 11.96% fat) compared to CON (37.81 + 9.26% CHO, 20.03 + 5.53% PRO, 37.47 + 11.80% fat). Fasting blood glucose levels (p = 0.017) were significantly lower in the CR (84.57 + 4.79 mg/dL) compared to the CON (93.28 + 6.90 mg/dL) yet there was no difference in blood TG levels (p = 0.177; 64.43 + 15.13 mg/dL vs. 59.29 + 14.16 mg/dL). Total average power output (p = 0.05) and total peak power output (p = 0.047) were significantly lower in the CR. CONCLUSION: While CDEX combined with CR may acutely reduce fasting blood glucose, this may be at the sacrifice of RE performance, especially during the initial phase of CR adaptation.