We hypothesized a differential activation of the anabolic signaling proteins protein kinase B (PKB) and p70 S6 kinase (p70S6K) and subsequent differential stimulation of human muscle protein synthesis (MPS) after dynamic shortening or lengthening exercise. Eight healthy men [25 ± 5 yr, BMI 26 ± 3 kg/m−2 (means ± SD)] were studied before and after 12 min of repeated stepping up to knee height, and down again, while carrying 25% of their body weight, i.e., shortening exercise with the “up” leg and lengthening exercise with contralateral “down” leg. Quadriceps biopsies were taken before and 3, 6, and 24 h after exercise. After exercise, over 2 h before the biopsies, the subjects ingested 500 ml of water containing 45 g of essential amino acids and 135 g of sucrose. Rates of muscle protein synthesis were determined via incorporation over time of [1-13C]leucine (≤6 h after exercise) or [1-13C]valine (21–24 h after exercise) and phosphorylation of signaling proteins by Western analysis. PKB and p70S6K phosphorylation increased ∼3-fold after 3 h and remained elevated at 6 and 24 h. After exercise, rates of myofibrillar and sarcoplasmic protein synthesis were unchanged over the period including exercise and 3 h of recovery but had increased significantly at 6 (∼3.0- and 2.4-fold, respectively) and 24 h (∼3.2- and 2.0-fold, respectively), independently of the mode of exercise. Short-term dynamic exercise in either shortening or lengthening mode increases MPS at least as much as resistance exercise and is associated with long-term activation of PKB and p70S6K.
Addition of Glutamine to Total Parenteral Nutrition After Elective Abdominal Surgery Spares Free Glutamine in Muscle, Counteracts the Fall in Muscle Protein Synthesis, and Improves Nitrogen Balance
