Search Results

You are looking at 21 - 30 of 40 items for

  • Author: Brian Dawson x
  • All content x
Clear All Modify Search
Restricted access

David B. Preen, Brian T. Dawson, Carmel Goodman, John Beilby, and Simon Ching

This study attempted to determine the relationship between creatine (Cr) accumulation in human skeletal muscle and erythrocytes following Cr supplementation. If a strong relationship exists, a blood test might provide a practical, less invasive alternative than muscle biopsy for evaluating cellular Cr accumulation. Eighteen active, but not well-trained males were supplemented with Cr (4 × 5g/d) for 5 d. Muscle biopsies (vastus lateralis) were obtained pre- and post-loading and analyzed for Cr, phosphocreatine (PCr), and total Cr (TCr) content. Venous blood was also drawn at these times to determine erythrocyte Cr concentrations. Muscle Cr, PCr, and TCr concentrations were elevated (P < 0.05) by 39.8%, 7.5%, and 20.1% respectively following supplementation. Erythrocyte Cr concentrations were also elevated (P < 0.01) following the loading period, although to a greater relative degree than tissue concentrations (129.6%). Pre- and post-loading erythrocyte Cr concentrations were poorly and nonsignificantly correlated with that observed in skeletal muscle. Further, loading-mediated increases in erythrocyte Cr concentrations were poorly correlated with elevations in muscle Cr (r = 0.07), PCr (r = 0.06) or TCr (r = 0.04) concentrations. Erythrocyte Cr concentrations can be augmented by 5 d of Cr supplementation, however, this elevation does not reflect that observed in skeletal muscle obtained by muscle biopsy. Consequently, erythrocyte response to Cr loading is not a reliable measure of skeletal muscle Cr/TCr accumulation.

Restricted access

Georgia M. Black, Tim J. Gabbett, Richard D. Johnston, Geraldine Naughton, Michael H. Cole, and Brian Dawson

Purpose: With female Australian football (AF) gaining popularity, understanding match demands is becoming increasingly important. The aim of this study was to compare running performances of rotated and whole-quarter state-level female AF players during match quarters. Methods : Twenty-two state-level female AF midfielders wore Global Positioning System units during 14 games to evaluate activity profiles. The Yo-Yo Intermittent Recovery Test Level 1 (Yo-Yo IR1) was used as a measure of high-intensity running ability. Data were categorized into whole quarter, rotation bout 1, and rotation bout 2 before being further divided into quartiles. Players were separated into high- or low-Yo-Yo IR1 groups using a median split based on their Yo-Yo IR1 performance. Short (4–6 min), moderate (6–12 min), and long (12–18 min) on-field bout activity profiles were compared with whole-quarter players. Results: High Yo-Yo IR1 performance allowed players to cover greater relative distances (ES = 0.57–0.88) and high-speed distances (ES = 0.57–0.86) during rotations. No differences were reported between Yo-Yo IR1 groups when players were required to play whole quarters (ES ≤ 0.26, likelihood ≤64%). Players who were on field for short to moderate durations exhibited greater activity profiles than whole-quarter players. Conclusions: Superior high-speed running ability results in a greater activity profile than for players who possess lower high-speed running ability. The findings also highlight the importance of short to moderate (4–12 min) rotation periods and may be used to increase high-intensity running performance within quarters in female AF players.

Restricted access

Benjamin M. Jackson, Ted Polglaze, Brian Dawson, Trish King, and Peter Peeling

Purpose: To compare data from conventional global positioning system (GPS-) and new global navigation satellite system (GNSS-) enabled tracking devices and to examine the interunit reliability of GNSS devices. Methods: Interdevice differences between 10-Hz GPS and GNSS devices were examined during laps (n = 40) of a simulated game circuit and during elite hockey matches (n = 21); GNSS interunit reliability was also examined during laps of the simulated game circuit. Differences in distance values and measures in 3 velocity categories (low <3 m·s−1; moderate 3–5 m·s−1; and high >5 m·s−1) and acceleration/deceleration counts (>1.46 and <−1.46 m·s−2) were examined using 1-way analysis of variance. Interunit GNSS reliability was examined using the coefficient of variation (CV) and intraclass correlation coefficient. Results: Interdevice differences (P < .05) were found for measures of peak deceleration, low-speed distance, percentage of total distance at low speed, and deceleration count during the simulated game circuit and for all measures except total distance and low-speed distance during hockey matches. Interunit (GNSS) differences (P < .05) were not found. The coefficient of variation was below 5% for total distance, average and peak speeds and distance and percentage of total distance of low-speed running. The GNSS devices had a lower horizontal dilution of precision score than GPS devices in all conditions. Conclusions: These findings suggest that GNSS devices may be more sensitive than GPS devices in quantifying the physical demands of team-sport movements, but further study into the accuracy of GNSS devices is required.

Restricted access

Georgia M. Black, Tim J. Gabbett, Rich D. Johnston, Michael H. Cole, Geraldine Naughton, and Brian Dawson

Purpose: The transition of female Australian football (AF) players from amateur to semielite competitions has the potential for athletes to be underprepared for match play. To gain an understanding of the match demands of female football, the aims of this study were to highlight the physical qualities that discriminate selected and nonselected female AF players, investigate activity profiles of female AF players, and gain an understanding of the influence of physical qualities on performance in female AF Methods: Twenty-two female AF state academy players (mean [SD]: age = 23.2 [4.5] y) and 27 nonselected players (mean [SD]: age = 23.4 [4.9] y) completed a Yo-Yo intermittent recovery test level 1, countermovement jump, and 30-m sprint tests were completed prior to the competitive season. During 14 matches, players wore global positioning system units to describe the running demands of match play. Results: Selected players were faster over 30 m (ES = 0.57; P = .04) and covered greater distances on the Yo-Yo IR1 (ES = 1.09; P < .001). Selected midfielders spent greater time on the field and covered greater total distances (ES = 0.73–0.85; P < .01). Players faster over 5 m (r = −.612) and 30 m (r = −.807) and who performed better on the Yo-Yo IR1 (r = .489) covered greater high-speed distances during match play. Conclusions: An emphasis should be placed on the development of physical fitness in this playing group to ensure optimal preparation for the national competition.

Restricted access

Amelia J. Carr, Gary J. Slater, Christopher J. Gore, Brian Dawson, and Louise M. Burke

Purpose:

The aim of this study was to determine the effect and reliability of acute and chronic sodium bicarbonate ingestion for 2000-m rowing ergometer performance (watts) and blood bicarbonate concentration [HCO3 ].

Methods:

In a crossover study, 7 well-trained rowers performed paired 2000-m rowing ergometer trials under 3 double-blinded conditions: (1) 0.3 grams per kilogram of body mass (g/kg BM) acute bicarbonate; (2) 0.5 g/kg BM daily chronic bicarbonate for 3 d; and (3) calcium carbonate placebo, in semi-counterbalanced order. For 2000-m performance and [HCO3 ], we examined differences in effects between conditions via pairwise comparisons, with differences interpreted in relation to the likelihood of exceeding smallest worthwhile change thresholds for each variable. We also calculated the within-subject variation (percent typical error).

Results:

There were only trivial differences in 2000-m performance between placebo (277 ± 60 W), acute bicarbonate (280 ± 65 W) and chronic bicarbonate (282 ± 65 W); however, [HCO3 ] was substantially greater after acute bicarbonate, than with chronic loading and placebo. Typical error for 2000-m mean power was 2.1% (90% confidence interval 1.4 to 4.0%) for acute bicarbonate, 3.6% (2.5 to 7.0%) for chronic bicarbonate, and 1.6% (1.1 to 3.0%) for placebo. Postsupplementation [HCO3 ] typical error was 7.3% (5.0 to 14.5%) for acute bicarbonate, 2.9% (2.0 to 5.7%) for chronic bicarbonate and 6.0% (1.4 to 11.9%) for placebo.

Conclusion:

Performance in 2000-m rowing ergometer trials may not substantially improve after acute or chronic bicarbonate loading. However, performances will be reliable with both acute and chronic bicarbonate loading protocols.

Restricted access

Brian Dawson, Carmel Goodman, Tanya Blee, Gary Claydon, Peter Peeling, John Beilby, and Alex Prins

Non-anemic, iron depleted women were randomly assigned to an injection group (IG) or oral group (OG) to assess which method is more efficient for increasing iron stores over a short time period. IG received a course of 5 × 2 mL intramuscular injections over 10 d, and OG received one tablet daily for 30 d. Fourteen, 21 and 28 d after commencing supplementation, ferritin concentration in OG significantly increased from baseline (means ± standard error: 27 ± 3 to 40 ± 5 to 41 ± 5 to 41 ± 5 µg/L; P < 0.01). Similarly, on days 15, 20, and 28 post the first injection, ferritin concentration in IG significantly increased from baseline (means ± standard error: 20 ± 2 to 71 ± 17 to 63 ± 11 to 63 ± 7 µg/L; P < 0.01), and was also significantly greater than OG at day 15 and 28 (P < 0.05). Iron injections are significantly more effective (both in time and degree of increase) in improving ferritin levels over 30 d than oral tablets.

Restricted access

Frankie Tan, Ted Polglaze, Gregory Cox, Brian Dawson, Iñigo Mujika, and Sally Clark

This study investigated the effects of sodium bicarbonate (NaHCO3) ingestion on simulated water polo match performance. Twelve elite players from the Australian National Women’s Water Polo Squad (age 23.7 ± 3.0 yr, height 1.73 ± 0.05 m, body mass 75.7 ± 8.0 kg) participated in the study. In a randomized cross-over double-blind design, players ingested 0.3 g/kg of NaHCO3 or placebo 90 min before performing a 59-min match-simulation test (MST) that included 56 × 10-m maximal-sprint swims as the performance measure. Capillary blood samples were obtained preingestion, pre- and post-warm-up, and after each quarter of the MST. Preexercise ingestion of NaHCO3 was effective in enhancing extracellular pH from baseline levels of 7.41; ±0.01 (M; ±90% confidence limits) to 7.49; ±0.01 and bicarbonate levels from 24.4; ±0.3 to 28.5; ±0.5 mmol/L. The percentage difference in mean sprint times between trials showed no substantial effects of NaHCO3 (0.4; ±1.0, effect size = 0.09; ±0.23; p = .51). These findings are contrary to those of previous NaHCO3 studies on simulated team-sport performance, but this investigation is unique in that it examined highly trained athletes performing sport-specific tasks. In conclusion, water polo players should not expect substantial enhancement in intermittent-sprint performance from NaHCO3 supplementation.

Restricted access

Carl Petersen, David B. Pyne, Marc R. Portus, Stuart Karppinen, and Brian Dawson

Purpose:

The time-motion characteristics and the within-athlete variability in movement patterns were quantified for the same male fast bowler playing One Day International (ODI) cricket matches (n = 12).

Methods:

A number of different time motion characteristics were monitored using a portable 5-Hz global positioning system (GPS) unit (Catapult, Melbourne, Australia).

Results:

The bowler’s mean workload per ODI was 8 ± 2 overs (mean ± SD). He covered a total distance of 15.9 ± 2.5 km per game; 12 ± 3% or 1.9 ± 0.2 km was striding (0.8 ± 0.2 km) or sprinting (1.1 ± 0.2 km), whereas 10.9 ± 2.1 km was spent walking. One high-intensity (running, striding, or sprinting) repetition (HIR) occurred every 68 ± 12 s, and the average duration of a HI effort was 2.7 ± 0.1 s. The player also completed 66 ± 11 sprints per game; mean sprint distance was 18 ± 3 m and maximum sprinting speed 8.3 ± 0.9 m·s−1.

Conclusions:

The movement patterns of this fast bowler were a combination of highly intermittent activities of variable intensity on the base of ~16 km per game. This information provides insight for conditioning coaches to determine the physical demands and to adapt the training and recovery processes of ODI fast bowlers.

Restricted access

Peter Peeling, Tanya Blee, Carmel Goodman, Brian Dawson, Gary Claydon, John Beilby, and Alex Prins

This investigation examined the effect of intramuscular iron injections on aerobic-exercise performance in iron-deficient women. Sixteen athletes performed a 10-min steady-state sub maximal economy test, a VO2max test, and a timed test to exhaustion at VO2max workload. Subjects were randomly assigned to an iron-supplemented group (IG) receiving intramuscular iron injections or to a placebo group (PG). Twenty days after the first injection, exercise and blood testing were repeated. A final blood test occurred on Day 28. Post supplementation, no differences were found between the groups’ sub maximal or maximal VO2, heart rate, or blood lactate (P > 0.05). Time to exhaustion was increased in the IG (P < 0.05) but was not greater than that of the PG (P > 0.05). The IG’s serum ferritin (SF) was significantly increased on Days 20 and 28 (mean ± standard error: 19 ± 3 to 65 ± 11 to 57 ± 12 µg/L; P < 0.01), with a percentage change from baseline significantly greater than in the PG (P < 0.01). It was concluded that intramuscular iron injections can effectively increase SF without enhancing sub maximal or maximal aerobic-exercise performance in iron-depleted female athletes.

Restricted access

Rachel McCormick, Alex Dreyer, Brian Dawson, Marc Sim, Leanne Lester, Carmel Goodman, and Peter Peeling

The authors compared the effectiveness of daily (DAY) versus alternate day (ALT) oral iron supplementation in athletes with suboptimal iron. Endurance-trained runners (nine males and 22 females), with serum ferritin (sFer) concentrations <50 μg/L, supplemented with oral iron either DAY or ALT for 8 weeks. Serum ferritin was measured at baseline and at fortnightly intervals. Hemoglobin mass (Hbmass) was measured pre- and postintervention in a participant subset (n = 10). Linear mixed-effects models were used to assess the effectiveness of the two strategies on sFer and Hbmass. There were no sFer treatment (p = .928) or interaction (p = .877) effects; however, sFer did increase (19.7 μg/L; p < .001) over the 8-week intervention in both groups. In addition, sFer was 21.2 μg/L higher (p < .001) in males than females. No Hbmass treatment (p = .146) or interaction (p = .249) effects existed; however, a significant effect for sex indicated that Hbmass was 140.85 g higher (p = .004) in males compared with females. Training load (p = .001) and dietary iron intake (p = .015) also affected Hbmass. Finally, there were six complaints of severe gastrointestinal side effects in DAY, but only one in ALT. In summary, both supplement strategies increased sFer in athletes with suboptimal iron status; however, the ALT approach was associated with lower incidence of gastrointestinal upset.