Daniel J. West

Relationships Between Force–Time Characteristics of the Isometric Midthigh Pull and Dynamic Performance in Professional Rugby League Players

West, DJ, Owen, NJ, Jones, MR, Bracken, RM, Cook, CJ, Cunningham, DJ, Shearer, DA, Finn, CV, Newton, RU, Crewther, BT, and Kilduff, LP. Relationships between force–time characteristics of the isometric midthigh pull and dynamic performance in professional rugby league players. J Strength Cond Res 25(11): 3070–3075, 2011—There is considerable conflict within the literature regarding the relevance of isometric testing for the assessment of neuromuscular function within dynamic sports. The aim of this study was to determine the relationship between isometric measures of force development and dynamic performance. Thirty-nine professional rugby league players participated in this study. Forty-eight hours after trial familiarization, participants performed a maximal isometric midthigh pull, with ∼120–130° bend at the knee, countermovement jump (CMJ), and a 10-m sprint. Force–time data were processed for peak force (PF), force at 100 milliseconds (F100ms), and peak rate of force development (PRFD). Analysis was carried out using Pearsons product moment correlation with significance set at p < 0.05. The PF was not related to dynamic performance; however, when expressed relative to body weight, it was significantly correlated with both 10-m time and CMJ height (r = −0.37 and 0.45, respectively, p < 0.05). The F100ms was inversely related to 10-m time (r = −0.54, p < 0.01); moreover, when expressed relative to body weight, it was significantly related to both 10-m time and CMJ height (r = −0.68 and 0.43, p < 0.01). In addition, significant correlations were found between PRFD and 10-m time (r = −0.66, p < 0.01) and CMJ height (r = 0.387, p < 0.01). In conclusion, this study provides evidence that measures of maximal strength and explosiveness from isometric force–time curves are related to jump and sprint acceleration performance in professional rugby league players.

Strength and Power Predictors of Swimming Starts in International Sprint Swimmers

West, DJ, Owen, NJ, Cunningham, DJ, Cook, CJ, and Kilduff, LP. Strength and power predictors of swimming starts in international sprint swimmers. J Strength Cond Res 25(4): 950-955, 2011-Start performance (as defined by time to 15 m) has been shown to be a key performance indicator during 50-m freestyle swimming; however, there is limited information with regard to the key strength and power variables that influence start performance during sprint swimming. In light of the above, this study aimed to examine the key strength and power predicators of start performance in 50-m freestyle swimming. Eleven male British international sprint swimmers (age 21.3 ± 1.7 years; mass 78.1 ± 11.2 kg; and height 1.8 ± 0.1 m) participated in this study. Within 1 week, swimmers performed the following tests: 3 repetition maximum (3RM) squat strength, countermovement jump (CMJ) on a portable force platform, and a measure of start time performance (time to 15 m under 50-m freestyle conditions). The start time was measured using a standard racing platform to which a portable force platform was mounted, and all starts were recorded using 2 cameras. This setup allowed for the quantification of time to 15 m, peak vertical force (PVF), and peak horizontal force (PHF). Data were analyzed using Pearsons product moment correlation with significance set at p < 0.05. Start time was significantly related to 1RM strength (r = −0.74), jump height (r = −0.69), peak (r = −0.85), and relative power (r = −0.66) (p < 0.05) but not rate of force development (r = −0.56, p > 0.05). Furthermore, lower body strength was a key determinant of jump height (r = 0.69), power (r = 0.78), PVF (r = 0.62), and PHF (r = 0.71) (p < 0.05). This study provides evidence of the importance of lower body strength and power to start time in international 50-m sprint swimmers.

The potential benefits of red beetroot supplementation in health and disease

In recent years there has been a growing interest in the biological activity of red beetroot (Beta vulgaris rubra) and its potential utility as a health promoting and disease preventing functional food. As a source of nitrate, beetroot ingestion provides a natural means of increasing in vivo nitric oxide (NO) availability and has emerged as a potential strategy to prevent and manage pathologies associated with diminished NO bioavailability, notably hypertension and endothelial function. Beetroot is also being considered as a promising therapeutic treatment in a range of clinical pathologies associated with oxidative stress and inflammation. Its constituents, most notably the betalain pigments, display potent antioxidant, anti-inflammatory and chemo-preventive activity in vitro and in vivo. The purpose of this review is to discuss beetroot’s biological activity and to evaluate evidence from studies that specifically investigated the effect of beetroot supplementation on inflammation, oxidative stress, cognition and endothelial function.

Effect of postactivation potentiation on swimming starts in international sprint swimmers

Kilduff, LP, Cunningham, DJ, Owen, NJ, West, DJ, Bracken, RM, and Cook, CJ. Effect of postactivation potentiation on swimming starts in international sprint swimmers. J Strength Cond Res 25(9): 2418-2423, 2011—The aim of this study was to investigate the effects of postactivation potentiation (PAP) on swim start performance (time to 15 m) in a group of international sprint swimmers. Nine international sprint swimmers (7 men and 2 women) volunteered and gave informed consent for this study, which was approved by the university ethics committee. Initially, swimmers performed a countermovement jump (CMJ) on a portable force platform (FP) at baseline and at the following time points ∼15 seconds, 4, 8, 12, and 16 minutes after a PAP stimulus (1 set of 3 repetitions at 87% 1 repetition maximum [RM]) to individually determine the recovery time required to observe enhanced muscle performance. On 2 additional days, swimmers performed a swim start to 15 m under 50-m freestyle race conditions, which was preceded by either their individualized race specific warm-up or a PAP stimulus (1 set of 3 repetitions at 87% 1RM). Both trials were recorded on 2 cameras operating at 50 Hz with camera 1 located at the start and camera 2 at the 15-m mark. Peak vertical force (PVF) and peak horizontal force (PHF) were measured during all swim starts from a portable FP placed on top of the swim block. A repeated measures analysis of variance revealed a significant time effect with regard to power output (PO) (F = 20.963, p < 0.01) and jump height (JH) (F = 14.634, p < 0.01) with a paired comparison indicating a significant increase in PO and JH after 8 minutes of recovery from the PAP stimulus. There was a significant increase in both PHF and PVF after the PAP stimulus compared to the swim-specific warm-up during the swim start (PHF 770 ± 228 vs. 814 ± 263 N, p = 0.018; PVF: 1,462 ± 280 vs. 1,518 ± 311 N, p = 0.038); however, time to 15 m was the same when both starts were compared (7.1 ± 0.8 vs. 7.1 ± 0.8 seconds, p = 0.447). The results from this study indicate that muscle performance during a CMJ is enhanced after a PAP stimulus providing adequate recovery (∼8 minutes) is given between the 2 activities. In addition, this study demonstrated that swimmers performed equally well in terms of time to 15 m when a PAP stimulus was compared to their individualized race specific warm-up and indicates that PAP may be a useful addition to a warm-up protocol before races. However, more research is required to fully understand the role PAP plays in swim performance.

Large Pre- and Postexercise Rapid-Acting Insulin Reductions Preserve Glycemia and Prevent Early- but Not Late-Onset Hypoglycemia in Patients With Type 1 Diabetes

OBJECTIVE To examine the acute and 24-h glycemic responses to reductions in postexercise rapid-acting insulin dose in type 1 diabetic patients. RESEARCH DESIGN AND METHODS After preliminary testing, 11 male patients (24 ± 2 years, HbA1c 7.7 ± 0.3%; 61 ± 3.4 mmol/mol) attended the laboratory on three mornings. Patients consumed a standardized breakfast (1 g carbohydrate ⋅ kg−1 BM; 380 ± 10 kcal) and self-administered a 25% rapid-acting insulin dose 60 min prior to performing 45 min of treadmill running at 72.5 ± 0.9% VO2peak. At 60 min postexercise, patients ingested a meal (1 g carbohydrate ⋅ kg−1 BM; 660 ± 21 kcal) and administered a Full, 75%, or 50% rapid-acting insulin dose. Blood glucose concentrations were measured for 3 h postmeal. Interstitial glucose was recorded for 20 h after leaving the laboratory using a continuous glucose monitoring system. RESULTS All glycemic responses were similar across conditions up to 60 min postexercise. After the postexercise meal, blood glucose was preserved under 50%, but declined under Full and 75%. Thence at 3 h, blood glucose was highest under 50% (50% [10.4 ± 1.2] vs. Full [6.2 ± 0.7] and 75% [7.6 ± 1.2 mmol ⋅ L−1], P = 0.029); throughout this period, all patients were protected against hypoglycemia under 50% (blood glucose ≤3.9; Full, n = 5; 75%, n = 2; 50%, n = 0). Fifty percent continued to protect patients against hypoglycemia for a further 4 h under free-living conditions. However, late-evening and nocturnal glycemia were similar; as a consequence, late-onset hypoglycemia was experienced under all conditions. CONCLUSIONS A 25% pre-exercise and 50% postexercise rapid-acting insulin dose preserves glycemia and protects patients against early-onset hypoglycemia (≤8 h). However, this strategy does not protect against late-onset postexercise hypoglycemia.

Insulin therapy and dietary adjustments to normalize glycemia and prevent nocturnal hypoglycemia after evening exercise in type 1 diabetes: a randomized controlled trial

Introduction Evening-time exercise is a frequent cause of severe hypoglycemia in type 1 diabetes, fear of which deters participation in regular exercise. Recommendations for normalizing glycemia around exercise consist of prandial adjustments to bolus insulin therapy and food composition, but this carries only short-lasting protection from hypoglycemia. Therefore, this study aimed to examine the impact of a combined basal-bolus insulin dose reduction and carbohydrate feeding strategy on glycemia and metabolic parameters following evening exercise in type 1 diabetes. Methods Ten male participants (glycated hemoglobin: 52.4±2.2 mmol/mol), treated with multiple daily injections, completed two randomized study-days, whereby administration of total daily basal insulin dose was unchanged (100%), or reduced by 20% (80%). Participants attended the laboratory at ∼08:00 h for a fasted blood sample, before returning in the evening. On arrival (∼17:00 h), participants consumed a carbohydrate meal and administered a 75% reduced rapid-acting insulin dose and 60 min later performed 45 min of treadmill running. At 60 min postexercise, participants consumed a low glycemic index (LGI) meal and administered a 50% reduced rapid-acting insulin dose, before returning home. At ∼23:00 h, participants consumed a LGI bedtime snack and returned to the laboratory the following morning (∼08:00 h) for a fasted blood sample. Venous blood samples were analyzed for glucose, glucoregulatory hormones, non-esterified fatty acids, β-hydroxybutyrate, interleukin 6, and tumor necrosis factor α. Interstitial glucose was monitored for 24 h pre-exercise and postexercise. Results Glycemia was similar until 6 h postexercise, with no hypoglycemic episodes. Beyond 6 h glucose levels fell during 100%, and nine participants experienced nocturnal hypoglycemia. Conversely, all participants during 80% were protected from nocturnal hypoglycemia, and remained protected for 24 h postexercise. All metabolic parameters were similar. Conclusions Reducing basal insulin dose with reduced prandial bolus insulin and LGI carbohydrate feeding provides protection from hypoglycemia during and for 24 h following evening exercise. This strategy is not associated with hyperglycemia, or adverse metabolic disturbances. Clinical trials number NCT02204839, ClinicalTrials.gov.

Neuromuscular function, hormonal, and mood responses to a professional rugby union match.

Abstract West, DJ, Finn, CV, Cunningham, DJ, Shearer, DA, Jones, MR, Harrington, BJ, Crewther, BT, Cook, CJ, and Kilduff, LP. Neuromuscular function, hormonal, and mood responses to a professional rugby union match. J Strength Cond Res 28(1): 194–200, 2014—We examined the recovery time-course of neuromuscular function (NMF), the testosterone and cortisol hormonal milieu, and mood for 60 hours after a competitive match in professional rugby union players (n = 14). Thirty-six hours prematch (19:30 hours kick-off), baseline saliva samples (testosterone, cortisol, and testosterone to cortisol [T/C] ratio), countermovement jump performances (peak power output [PPO]), and mood disruption (Brief Assessment of Mood Questionnaire) were collected and was repeated at 12, 36, and 60 hours postmatch. Peak power output decreased below baseline at 12 hours (baseline 6,100 ± 565 W vs. 12 h 5,680 ± 589 W; p = 0.004) and 36 hours (5,761 ± 639 W; p < 0.001) but had recovered at 60 hours (5,950 ± 505 W; p = 0.151). Cortisol concentrations increased from baseline at 12 hours (baseline 0.40 ± 0.09 µg·dl−1 vs. 12 h 0.60 ± 0.20 µg·dl−1; p = 0.004) and 36 hours (0.60 ± 0.20 µg·dl−1; p = 0.027) but were similar at 60 hours postmatch. Testosterone concentrations decreased from baseline at 12 hours (baseline 214 ± 84 pg·ml−1 vs. 12 h 151 ± 56 pg·ml−1; p = 0.023) and 36 hours (173 ± 71 pg·ml−1; p = 0.016) but were similar at 60 hours postmatch. The T/C ratio decreased from baseline at 12 hours (baseline 551 ± 219 vs. 12 h 266 ± 123; p = 0.001) and 36 hours (310 ± 148; p = 0.027) before returning to baseline at 60 hours postmatch. Mood disturbance increased at 12 hours (p = 0.031) before returning to baseline at 36 and 60 hours postmatch. There were no relationships between changes in PPO, testosterone, cortisol, T/C ratio, and mood. In conclusion, postmatch changes in NMF, salivary hormones, and mood disturbance were identified in professional rugby union players. Players and coaches can expect reduced NMF and hormonal disruption for 36 hours before recovering at 60 hours postmatch, with mood recovered by 36 hours postmatch. Knowledge of these recovery time-courses may prove useful for player training program design and postmatch recovery strategies.

Morning based strength training improves afternoon physical performance in rugby union players.

OBJECTIVES To determine if a morning training session could alter afternoon physical performance. Moreover, as testosterone (T) and cortisol (C) concentrations are significant predictors of physical performance, and both show circadian declines across the day, we examined the effects of morning training on diurnal T and C responses. DESIGN Eighteen semi-professional rugby union players completed this randomised and counter-balanced study. METHODS Following morning saliva collection (0900 h), players completed a control (rested), Sprint (5 × 40 m) or Weights (3 repetition-maximum [RM] bench press and squat) trial. In the afternoon (15:00 h) of each trial, a further saliva sample was collected before players completed a performance test (3 RM back squat and bench press, 40 m sprint, countermovement jump [CMJ]). RESULTS Salivary T concentrations declined from am to pm under Control and Sprint, but not under Weights. Delta T, from am to pm, was greater under Control (-10.9 ± 2.4 pg ml(-1)) compared to Sprints (-6.2 ± 7.1 pg ml(-1)) and Weights (-1.2 ± 5.5 pg ml(-1)) (p ≤ 0.001). Delta C, from am to pm, was greater under Control compared to both Sprint and Weights (p<0.05). Players elicited better CMJ peak power, 40-m time, 3 RM bench and squat performance under Weights compared with Control and Sprint (p<0.05). Faster 40-m times were seen under Sprint, when compared to Control (p<0.05). CONCLUSIONS Performing morning strength training is associated with improved physical performance in the afternoon. Additionally, the circadian decline in T concentrations appeared offset by morning training. However, it is unclear if T concentrations are, in part, causal of these improved responses or simply a reflective marker.

The influence of passive heat maintenance on lower body power output and repeated sprint performance in professional rugby league players

OBJECTIVES The pre-competition warm-up mediates many temperature related physiological changes which generally lead to an improvement in performance. However, after ceasing exercise body temperature declines rapidly, which reduces some of the benefits of the initial warm-up. We examined the effects of a passive heat maintenance strategy on post-warm-up core temperature (Tcore) and performance in professional rugby league players. DESIGN Twenty professional rugby league players completed this randomised and counter-balanced study. METHODS After a standardised warm-up, players completed a countermovement jump (CMJ) before resting for 15min wearing normal training attire (control) or wearing a passive heat maintenance jacket (PHM), players then completed another CMJ and a repeated sprint protocol (RSA). Tcore was measured at baseline, post-warm-up, pre-RSA and post-RSA. CMJ were analysed for peak power output (PPO), and RSA for fastest, mean and total sprint time. RESULTS Post-warm-up Tcore (mean±SD; control 37.70±0.28; PHM 37.70±0.27°C; p=0.741) and PPO (control 5220±353 vs. PHM 5213±331W; p=0.686) were similar between conditions. At pre-RSA, PHM was associated with greater Tcore (control 37.14±0.31 vs. PHM 37.51±0.30°C; p<0.001) and PPO (control 4868±345 vs. PHM 5056±344W; p<0.001) when compared to control. The decline in PPO from post-warm-up to pre-RSA was related to the drop in Tcore (r=0.71; p<0.001). During the RSA, fastest, mean and total sprint time were all improved under PHM compared to control (p<0.05). CONCLUSIONS Passive heat maintenance is an effective method of attenuating the post-warm-up decline in Tcore and improves PPO and repeated sprint ability in professional rugby league players.

Quantifying positional and temporal movement patterns in professional rugby union using global positioning system

Abstract This study assessed the positional and temporal movement patterns of professional rugby union players during competition using global positioning system (GPS) units. GPS data were collected from 33 professional rugby players from 13 matches throughout the 2012–2013 season sampling at 10 Hz. Players wore GPS units from which information on distances, velocities, accelerations, exertion index, player load, contacts, sprinting and repeated high-intensity efforts (RHIE) were derived. Data files from players who played over 60 min (n = 112) were separated into five positional groups (tight and loose forwards; half, inside and outside backs) for match analysis. A further comparison of temporal changes in movement patterns was also performed using data files from those who played full games (n = 71). Significant positional differences were found for movement characteristics during performance (P < 0.05). Results demonstrate that inside and outside backs have greatest high-speed running demands; however, RHIE and contact demands are greatest in loose forwards during match play. Temporal analysis of all players displayed significant differences in player load, cruising and striding between halves, with measures of low- and high-intensity movement and acceleration/deceleration significantly declining throughout each half. Our data demonstrate significant positional differences for a number of key movement variables which provide a greater understanding of positional requirements of performance. This in turn may be used to develop progressive position-specific drills that elicit specific adaptations and provide objective measures of preparedness. Knowledge of performance changes may be used when developing drills and should be considered when monitoring and evaluating performance.