Sodium citrate induces alkalosis and can provide a performance benefit in high-intensity exercise. Previous investigations have been inconsistent in the ingestion protocols used, in particular the dose and timing of ingestion before the onset of exercise. The primary aim of the current study was to quantify blood pH, blood bicarbonate concentration and gastrointestinal symptoms after ingestion of three doses of sodium citrate (500 mg⋅kg-1, 700 mg⋅kg-1 and 900 mg⋅kg-1). Thirteen participants completed four experimental sessions, each consisting of a different dose of sodium citrate or a taste-matched placebo solution. Blood pH and blood bicarbonate concentration were measured at 30-min intervals via analysis of capillary blood samples. Gastrointestinal symptoms were also monitored at 30-min intervals. Statistical significance was accepted at a level of p < .05. Both measures of alkalosis were significantly greater after ingestion of sodium citrate compared with placebo (p < .001). No significant differences in alkalosis were found between the three sodium citrate doses (p > .05). Peak alkalosis following sodium citrate ingestion ranged from 180 to 212 min after ingestion. Gastrointestinal symptoms were significantly higher after sodium citrate ingestion compared with placebo (p < .001), while the 900 mg.kg-1 dose elicited significantly greater gastrointestinal distress than 500 mg⋅kg-1 (p = .004). It is recommended that a dose of 500 mg⋅kg-1 of sodium citrate should be ingested at least 3 hr before exercise, to achieve peak alkalosis and to minimize gastrointestinal symptoms before and during exercise.
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Charles S. Urwin, Dan B. Dwyer, and Amelia J. Carr
Jared A. Bailey, Paul B. Gastin, Luke Mackey, and Dan B. Dwyer
Context:
Most previous investigations of player load in netball have used subjective methodologies, with few using objective methodologies. While all studies report differences in player activities or total load between playing positions, it is unclear how the differences in player activity explain differences in positional load.
Purpose:
To objectively quantify the load associated with typical activities for all positions in elite netball.
Methods:
The player load of all playing positions in an elite netball team was measured during matches using wearable accelerometers. Video recordings of the matches were also analyzed to record the start time and duration of 13 commonly reported netball activities. The load associated with each activity was determined by time-aligning both data sets (load and activity).
Results:
Off-ball guarding produced the highest player load per instance, while jogging produced the greatest player load per match. Nonlocomotor activities contributed least to total match load for attacking positions (goal shooter [GS], goal attack [GA], and wing attack [WA]) and most for defending positions (goalkeeper [GK], goal defense [GD], and wing defense [WD]). Specifically, centers (Cs) produced the greatest jogging load, WA and WD accumulated the greatest running load, and GS and WA accumulated the greatest shuffling load. WD and Cs accumulated the greatest guarding load, while WD and GK accumulated the greatest off-ball guarding load.
Conclusions:
All positions exhibited different contributions from locomotor and nonlocomotor activities toward total match load. In addition, the same activity can have different contributions toward total match load, depending on the position. This has implications for future design and implementation of position-specific training programs.
Darcy M. Brown, Dan B. Dwyer, Samuel J. Robertson, and Paul B. Gastin
The purpose of this study was to assess the validity of a global positioning system (GPS) tracking system to estimate energy expenditure (EE) during exercise and field-sport locomotor movements. Twenty-seven participants each completed a 90-min exercise session on an outdoor synthetic futsal pitch. During the exercise session, they wore a 5-Hz GPS unit interpolated to 15 Hz and a portable gas analyzer that acted as the criterion measure of EE. The exercise session was composed of alternating 5-minute exercise bouts of randomized walking, jogging, running, or a field-sport circuit (×3) followed by 10 min of recovery. One-way analysis of variance showed significant (P < .01) and very large underestimations between GPS metabolic power– derived EE and oxygen-consumption (VO2) -derived EE for all field-sport circuits (% difference ≈ –44%). No differences in EE were observed for the jog (7.8%) and run (4.8%), whereas very large overestimations were found for the walk (43.0%). The GPS metabolic power EE over the entire 90-min session was significantly lower (P < .01) than the VO2 EE, resulting in a moderate underestimation overall (–19%). The results of this study suggest that a GPS tracking system using the metabolic power model of EE does not accurately estimate EE in field-sport movements or over an exercise session consisting of mixed locomotor activities interspersed with recovery periods; however, is it able to provide a reasonably accurate estimation of EE during continuous jogging and running.
Christopher M. Young, Paul B. Gastin, Nick Sanders, Luke Mackey, and Dan B. Dwyer
Context:
The activity profile of competition and training in elite netball has not been comprehensively reported in the literature.
Purpose:
To measure and analyze player load in elite netballers during matches and training sessions. The primary research question was, How does player load vary between playing positions in a match and between matches and training sessions?
Methods:
Various measures of player load were recorded in 12 elite professional netballers with a mean ± SD age of 26 ± 4.9 y and height of 183.2 ± 8.7 cm. Player load was assessed using a published method that uses accelerometry. Load was represented as total load in arbitrary units (au), playing intensity (au/min), and relative time spent in each of 4 playing intensity zones (low, low to moderate, moderate, and high). Data from 15 games and up to 17 training sessions were analyzed for each player.
Results:
Player load in matches for the goal-based positions (goal shooter, goal keeper, and goal defense) tended to be lower than the attacking and wing-based positions (goal attack, wing attack, wing defense, and center). The difference was largely due to the amount of time spent in low-intensity activity. Playing intensity of matches was greater than in training sessions; however, the total time spent in moderate- to high-intensity activities was not practically different.
Conclusions:
Accelerometry is a valuable method of measuring player load in netball, and the present results provide new information about the activity profile of different playing positions.
Ryan T. Letter, Dan B. Dwyer, Eric J. Drinkwater, and Simon A. Feros
Purpose: To determine whether the most important physical qualities in elite Australian male and female cricket pace bowlers change with age and phase of the cricket season. Methods: An existing longitudinal database (7 cricket seasons) of selected and routinely collected physical testing data from 103 male and 58 female elite Australian pace bowlers age 18–30 years was retrospectively analyzed. Male and female physical testing data from the isometric midthigh pull, 1-repetition-maximum bench pull, run-of-3, and countermovement jump (male only) were analyzed separately by performing linear mixed models on each of the physical qualities. Type III analysis-of-variance tests were conducted to determine if a significant effect existed within the fixed effects of age, season phase, and the age × season phase interaction. Appropriate pairwise comparisons were conducted. Results: Absolute and relative measures of force in the isometric midthigh pull and strength in the 1-repetition-maximum bench pull tests were significantly greater in older male and female pace bowlers. Older male pace bowlers demonstrated significantly faster absolute and relative best run-of-3 times. Conclusions: Most physical qualities across both male and female pace bowlers demonstrated an improvement with age. This is likely due to a training effect and would be anticipated to lead to a gradual enhancement of ball release speed, in accordance with previous research. Future research should look to investigate the relationship between the development of physical qualities and ball release speed among elite male and female pace bowlers.
Ryan T. Letter, Dan B. Dwyer, Eric J. Drinkwater, and Simon A. Feros
Purpose: This study investigated the differences between selected physical attributes and ball release speed in slower and faster male and female elite pace bowlers. Methods: Twelve physical attributes and ball release speed were retrospectively analyzed from 63 male and 31 female elite pace bowlers over the course of 5 seasons. Pace bowlers were categorized as either fast (>122.9 km/h, males and >97.8 km/h, females) or slow (<122.9 km/h, males and <97.8 km/h, females) for each sex. Differences in physical attributes between slower and faster bowling groups were compared using Cohen d effect sizes. Results: Faster pace bowlers displayed differences in isometric midthigh-pull peak force (d = 0.25, males and d = 0.68, females) and relative peak force (d = 0.62, males and d = 0.77, females). Faster male pace bowlers displayed differences in relative (d = 0.61) and absolute (d = 0.39) countermovement jump heights. Faster female pace bowlers displayed differences in 1-repetition-maximum bench-pull strength (d = 0.45) and run-of-3 performance (relative average, d = 1.22; relative best, d = 1.12; average, d = 0.49; and best, d = 0.40). Conclusions: Anaerobic dominant physical attributes appear to be important in both male and female pace bowlers. The contribution of these physical attributes to ball release speed appears to differ slightly between males and females. Lower-body strength (males and females), lower-body power (males), relative anaerobic capacities (females), and upper-body strength (females) appear to distinguish between slower and faster elite pace bowlers.
