Comment on: "Changes in Skeletal Muscle Glycogen Content in Professional Soccer Players before and after a Match by a NonInvasive MuscleSound® Technology. A Cross Sectional Pilot Study Nutrients 2020, 12(4), 971".

San-Millán and colleagues [...].

Training Load and Carbohydrate Periodization Practices of Elite Male Australian Football Players: Evidence of Fueling for the Work Required.

The authors aimed to quantify (a) the periodization of physical loading and daily carbohydrate (CHO) intake across an in-season weekly microcycle of Australian Football and (b) the quantity and source of CHO consumed during game play and training. Physical loading (via global positioning system technology) and daily CHO intake (via a combination of 24-hr recall, food diaries, and remote food photographic method) were assessed in 42 professional male players during two weekly microcycles comprising a home and away fixture. The players also reported the source and quantity of CHO consumed during all games (n = 22 games) and on the training session completed 4 days before each game (n = 22 sessions). The total distance was greater (p < .05) on game day (GD; 13 km) versus all training days. The total distance differed between training days, where GD-2 (8 km) was higher than GD-1, GD-3, and GD-4 (3.5, 0, and 7 km, respectively). The daily CHO intake was also different between training days, with reported intakes of 1.8, 1.4, 2.5, and 4.5 g/kg body mass on GD-4, GD-3, GD-2, and GD-1, respectively. The CHO intake was greater (p < .05) during games (59 ± 19 g) compared with training (1 ± 1 g), where in the former, 75% of the CHO consumed was from fluids as opposed to gels. Although the data suggest that Australian Football players practice elements of CHO periodization, the low absolute CHO intakes likely represent considerable underreporting in this population. Even when accounting for potential underreporting, the data also suggest Australian Football players underconsume CHO in relation to the physical demands of training and competition.

Ultrasound Does Not Detect Acute Changes in Glycogen in Vastus Lateralis of Man.

PURPOSE: To examine the validity of ultrasound (via cloud-based software that measures pixilation intensity according to a scale of 0-100) to noninvasively assess muscle glycogen in human skeletal muscle. METHODS: In study 1, 14 professional male rugby league players competed in an 80-min competitive rugby league game. In study 2 (in a randomized repeated measures design), 16 recreationally active males completed an exhaustive cycling protocol to deplete muscle glycogen followed by 36 h of HIGH or LOW carbohydrate intake (8 g·kg vs 3 g·kg body mass). In both studies, muscle biopsies and ultrasound scans were obtained from the vastus lateralis (at 50% of the muscle length) before and after match play in study 1 and at 36 h after glycogen depletion in study 2. RESULTS: Despite match play reducing (P < 0.01) muscle glycogen concentration (pregame: 443 ± 65; postgame: 271 ± 94 mmol·kg dw, respectively) in study 1, there were no significant changes (P = 0.4) in ultrasound scores (pregame: 47 ± 6, postgame: 49 ± 7). In study 2, muscle glycogen concentration was significantly different (P < 0.01) between HIGH (531 ±129 mmol·kg dw) and LOW (252 ± 64 mmol·kg dw) yet there was no difference (P = 0.9) in corresponding ultrasound scores (HIGH: 56 ± 7, LOW: 54 ± 6). In both studies, no significant correlations (P > 0.05) were present between changes in muscle glycogen concentration and changes in ultrasound scores. CONCLUSIONS: Data demonstrate that ultrasound (as based on measures of pixilation intensity) is not valid to measure muscle glycogen status within the physiological range (i.e., 200-500 mmol·kg dw) that is applicable to exercise-induced muscle glycogen utilization and postexercise muscle glycogen resynthesis.

Muscle Glycogen Utilization During an Australian Rules Football Game.

PURPOSE: To better understand the carbohydrate (CHO) requirement of Australian Football (AF) match play by quantifying muscle glycogen utilization during an in-season AF match. METHODS: After a 24-h CHO-loading protocol of 8 and 2 g/kg in the prematch meal, 2 elite male forward players had biopsies sampled from m. vastus lateralis before and after participation in a South Australian Football League game. Player A (87.2 kg) consumed water only during match play, whereas player B (87.6 kg) consumed 88 g CHO via CHO gels. External load was quantified using global positioning system technology. RESULTS: Player A completed more minutes on the ground (115 vs 98 min) and covered greater total distance (12.2 vs 11.2 km) than player B, although with similar high-speed running (837 vs 1070 m) and sprinting (135 vs 138 m). Muscle glycogen decreased by 66% in player A (pre: 656 mmol/kg dry weight [dw], post: 223 mmol/kg dw) and 24% in player B (pre: 544 mmol/kg dw, post: 416 mmol/kg dw). CONCLUSION: Prematch CHO loading elevated muscle glycogen concentrations (ie, >500 mmol/kg dw), the magnitude of which appears sufficient to meet the metabolic demands of elite AF match play. The glycogen cost of AF match play may be greater than in soccer and rugby, and CHO feeding may also spare muscle glycogen use. Further studies using larger sample sizes are now required to quantify the interindividual variability of glycogen cost of match play (including muscle and fiber-type-specific responses), as well examining potential metabolic and ergogenic effects of CHO feeding.

Position specific differences in the anthropometric characteristics of elite European Super League rugby players.

Rugby league is a collision sport which traditionally adopts a large emphasis on lean muscle mass. Currently there is limited research on the anthropometry of European Super League players. The aim of this study was to assess body composition using Dual Energy X-ray Absorptiometry (DXA) scans to identify the typical profile of elite rugby league players. One hundred and twelve players from five different clubs competing in the European Super League were recruited for the study. DXA scans were performed and the total mass, lean mass, fat mass and percentage body fat were reported for each positional group. For the Fullback and Wingers, Centres, Half Backs, Hookers, Props and Back Row Forwards the mean (SD) body fat percentage was 13 (2.1), 13 (2.4), 12 (3.4), 15 (3.9), 16 (4.3) and 15 (2.1)%, respectively, and total mass was 86 (8.2), 91 (6.6), 81 (8), 84 (9.5) 102 (8.5) and 93 (5.5) kg, respectively. Despite small to very large inter positional differences in all anthropometric variables (effect sizes = -0.08 to 2.56), particularly between the Prop and the other playing positions, there was large intra-position variation in body fat, lean mass and total mass making a standardised position specific profile difficult to establish. When used with other key performance indicators, these data provide the first multi-team anthropometric profile of elite Super League players that can be used to guide individualised training and nutrition practices for current and aspiring athletes.