Sunday, April 20, 2014

Recent studies with applications to real life sporting settings

Vitamin C and E supplementation hampers cellular adaptation to endurance training in humans

FREE to download from the Journal of Physiology

Paulsen et al. J Physiol 2014;592:1887-1901

In this double-blind, randomised, controlled trial, we investigated the effects of vitamin C and E supplementation on endurance training adaptations in humans. Fifty-four young men and women were randomly allocated to receive either 1000 mg of vitamin C and 235 mg of vitamin E or a placebo daily for 11 weeks. During supplementation, the participants completed an endurance training programme consisting of three to four sessions per week (primarily of running), divided into high-intensity interval sessions [4-6 × 4-6 min; >90% of maximal heart rate (HRmax)] and steady state continuous sessions (30-60 min; 70-90% of HRmax). Maximal oxygen uptake (VO2 max ), submaximal running and a 20 m shuttle run test were assessed and blood samples and muscle biopsies were collected, before and after the intervention. Participants in the vitamin C and E group increased their VO2 max (mean ± s.d.: 8 ± 5%) and performance in the 20 m shuttle test (10 ± 11%) to the same degree as those in the placebo group (mean ± s.d.: 8 ± 5% and 14 ± 17%, respectively). However, the mitochondrial marker cytochrome c oxidase subunit IV (COX4) and cytosolic peroxisome proliferator-activated receptor-γ coactivator 1 α (PGC-1α) increased in the m. vastus lateralis in the placebo group by 59 ± 97% and 19 ± 51%, respectively, but not in the vitamin C and E group (COX4: -13 ± 54%; PGC-1α: -13 ± 29%; P ≤ 0.03, between groups). Furthermore, mRNA levels of CDC42 and mitogen-activated protein kinase 1 (MAPK1) in the trained muscle were lower in the vitamin C and E group than in the placebo group (P ≤ 0.05). Daily vitamin C and E supplementation attenuated increases in markers of mitochondrial biogenesis following endurance training. However, no clear interactions were detected for improvements in VO2 max and running performance. Consequently, vitamin C and E supplementation hampered cellular adaptations in the exercised muscles, and although this did not translate to the performance tests applied in this study, we advocate caution when considering antioxidant supplementation combined with endurance exercise.

Burns KJ, Pollock BS, Lascola P, McDaniel J. Cardiovascular responses to counterweighted single-leg cycling: implications for rehabilitation. Eur J Appl Physiol. 2014 May;114(5):961-8. 

PURPOSE: Although difficult to coordinate, single-leg cycling allows for greater muscle-specific exercise capacity and subsequently greater stimulus for metabolic and vascular adaptations compared to typical double-leg cycling. The purpose of this investigation was to compare metabolic, cardiovascular and perceptual responses of double-leg cycling to single-leg cycling with and without the use of a counterweight. METHODS: Ten healthy individuals (age 22 ± 2 years; body mass 78.0 ± 11.2 kg; height 1.8 ± 0.1 m) performed three cycling conditions consisting of double-leg cycling (DL), non-counterweighted single-leg cycling (SLNCW) and single-leg cycling with a 97 N counterweight attached to the unoccupied crank arm (SLCW). For each condition, participants performed cycling trials (80 rpm) at three different work rates (40, 80 and 120 W). Oxygen consumption (VO2), respiratory exchange ratio (RER), heart rate (HR), femoral blood flow, rating of perceived exertion (RPE) and liking score were measured. RESULTS: VO2 and HR were similar for DL and SLCW conditions. However, during SLNCW, VO2 was at least 23 ± 13 % greater and HR was at least 15 ± 11 % greater compared to SLCW across all three intensities. Femoral blood flow was at least 65.5 ± 43.8 % greater during SLCW compared to DL cycling across all three intensities. RPE was lower and liking scores were greater for SLCW compared to SLNCW condition. CONCLUSION: Counterweighted single-leg cycling provides an exercise modality that is more tolerable than typical single-leg cycling while inducing greater peripheral stress for the same cardiovascular demand as double-leg cycling.

Nilstad A, Bahr R, Andersen TE. Text messaging as a new method for injury registration in sports: a methodological study in elite female football. Scand J Med Sci Sports. 2014 Feb;24(1):243-9.

Methodological differences in epidemiologic studies have led to significant discrepancies in injury incidences reported. The aim of this study was to evaluate text messaging as a new method for injury registration in elite female football players and to compare this method with routine medical staff registration. Twelve teams comprising 228 players prospectively recorded injuries and exposure through one competitive football season. Players reported individually by answering three text messages once a week. A designated member of the medical staff conducted concurrent registrations of injuries and exposure. Injuries and exposure were compared between medical staff registrations from nine teams and their 159 affiliated players. During the football season, a total of 232 time-loss injuries were recorded. Of these, 62% were captured through individual registration only, 10% by the medical staff only, and 28% were reported through both methods. The incidence of training injuries was 3.7 per 1000 player hours when calculated from individual registration vs 2.2 from medical staff registration [rate ratio (RR): 1.7, 1.2-2.4]. For match injuries, the corresponding incidences were 18.6 vs 5.4 (RR: 3.4, 2.4-4.9), respectively. There was moderate agreement for severity classifications in injury cases reported by both methods (kappa correlation coefficient: 0.48, confidence interval: 0.30-0.66).

Areta JL, Burke LM, Camera DM et al. Reduced resting skeletal muscle protein synthesis is rescued by resistance exercise and protein ingestion following short-term energy deficit. Am J Physiol Endocrinol Metab 2014;306:E989-997

The myofibrillar protein synthesis (MPS) response to resistance exercise (REX) and protein ingestion during energy deficit (ED) is unknown. In young men (n = 8) and women (n = 7), we determined protein signaling and resting postabsorptive MPS during energy balance [EB; 45 kcal·kg fat-free mass (FFM)(-1)·day(-1)] and after 5 days of ED (30 kcal·kg FFM(-1)·day(-1)) as well as MPS while in ED after acute REX in the fasted state and with the ingestion of whey protein (15 and 30 g). Postabsorptive rates of MPS were 27% lower in ED than EB (P < 0.001), but REX stimulated MPS to rates equal to EB. Ingestion of 15 and 30 g of protein after REX in ED increased MPS ∼16 and ∼34% above resting EB (P < 0.02). p70 S6K Thr(389) phosphorylation increased above EB only with combined exercise and protein intake (∼2-7 fold, P < 0.05). In conclusion, short-term ED reduces postabsorptive MPS; however, a bout of REX in ED restores MPS to values observed at rest in EB. The ingestion of protein after REX further increases MPS above resting EB in a dose-dependent manner. We conclude that combining REX with increased protein availability after exercise enhances rates of skeletal muscle protein synthesis during short-term ED and could in the long term preserve muscle mass.

No comments: