Effect of carbohydrate-electrolyte feedings on knee biomechanics and postural stability during intermittent highintensity exercise to fatigue

Fatiguing exercise alters neuromuscular and biomechanical characteristics that increase athlete's risk for non-contact lower extremity injury. Sports nutrition research has demonstrated the ability to delay fatigue and improve performance through carbohydrate feedings. However, the effect of nutrition on delaying neuromuscular risk factors affected by exercise and fatigue has not been examined. The purpose of this study was to evaluate the effects of a carbohydrate-electrolyte (CHO-E) beverage compared to a placebo (PLA) on landing kinematics, balance, and muscle activation patterns throughout an intermittent high-intensity exercise (IHE) protocol. The IHE protocol was designed to mimic sports competition and has demonstrated the ability to induce changes in landing mechanics during pilot testing. A total of 24 (12 male/12 female) athletes (age: 23.0+/-4.0yrs; height: 173.3+/-7.1cm; weight: 72.9+/-11.5kg; body fat: 18.0+/-6.4%) completed three days of testing. The first day of testing consisted of anthropometrics and familiarization with the IHE protocol. The next two testing sessions participants performed four quarters of IHE while consuming either a CHO-E or PLA beverage. Landing kinematics, muscle activation, and dynamic postural stability index (DPSI) scores were assessed immediately before, at break three, and break four of the IHE protocol. The DPSI scores were measured during a single-leg jump landing. Landing kinematics (knee flexion and valgus/varus at initial contact, and peak hip flexion) and muscle activity (surface electromyography pre-activity and re-activity of the hamstrings and quadriceps) were measured during a single-leg stop-jump. Separate two-way repeated measures analysis of variance was performed to determine the interaction between time and treatment for landing kinematics and DPSI. Change in muscle activation was examined using a related samples Wilcoxon Signed Rank test. The CHO-E beverage had no effect on preventing changes in knee flexion at initial contact (p=0.472), peak hip flexion (p=0.456), and muscle activation (p>0.05). A significant interaction effect occurred for DPSI scores (p=0.023) and knee valgus/varus at initial contact (p=0.007) however, these changes were small and lack clinical significance. Consuming a 6% CHO-E beverage before, during, and after IHE had no effect on preventing neuromuscular/biomechanical changes occurring as a result of IHE. Future studies should continue to investigate nutritional approaches for injury prevention.