Peter I. Brown

The effect of warm-up on high-intensity, intermittent running using nonmotorized treadmill ergometry

The aim of this study was to investigate the effect of previous warming on high-intensity intermittent running using nonmotorized treadmill ergometry. Ten male soccer players completed a repeated sprint test (10 × 6-second sprints with 34-second recovery) on a nonmotorized treadmill preceded by an active warm-up (10 minutes of running: 70% &OV0312;o2max; mean core temperature (Tc) 37.8 ± 0.2°C), a passive warm-up (hot water submersion: 40.1 ± 0.2°C until Tc reached that of the active warm-up; 10 minutes ± 23 seconds), or no warm-up (control). All warm-up conditions were followed by a 10-minute static recovery period with no stretching permitted. After the 10-minute rest period, Tc was higher before exercise in the passive trial (38.0 ± 0.2°C) compared to the active (37.7 ± 0.4°C) and control trials (37.2 ± 0.2°C; p < 0.05). There were no differences in pre-exercise oxygen consumption and blood lactate concentration; however, heart rate was greater in the active trial (p < 0.05). The peak mean 1-second maximum speed (MxSP) and group mean MxSP were not different in the active and passive trials (7.28 ± 0.12 and 7.16 ± 0.10 m·s−1, respectively, and 7.07 ± 0.33 and 7.02 ± 0.24 m·s−1, respectively; p > 0.05), although both were greater than the control. The percentage of decrement in performance fatigue was similar between all conditions (active, 3.4 ± 1.3%; passive, 4.0 ± 2.0%; and control, 3.7 ± 2.4%). We conclude that there is no difference in high-intensity intermittent running performance when preceded by an active or passive warm-up when matched for post-warm-up Tc. However, repeated sprinting ability is significantly improved after both active and passive warm-ups compared to no warm-up.

Preloaded time trial to assess load carriage performance.

Abstract Faghy, MA and Brown, PI. Preloaded time trial to assess load carriage performance. J Strength Cond Res 28(12): 3354–3362, 2014—The relevance and importance of load carriage in recreational and occupational tasks has stimulated a large body of research. Exercise protocols have been criticized for a lack of relevance to occupational activities; accordingly, the aim of this study was to assess the reliability of a preloaded time-trial protocol for load carriage assessment. After full familiarization, 8 healthy males performed 2 trials separated by 1 week. Each trial comprised 60-minute walking at 6.5 km·h−1 and 0% gradient (LC), 15 minutes seated recovery followed by a 2.4-km time-trial (LCTT). All trials were performed wearing a 25-kg backpack. Performance time was 16.71 ± 1.82 minutes and 16.37 ± 1.78 minutes for LCTT 1 and 2, respectively with a mean difference of −0.34 ± 0.89 minutes. Using log ratio limits of agreement, the mean bias was 1.02 and random error component of the agreement ratio was 1.11. The intraclass correlation was 0.85, coefficient of variation was 10.5%, and Cohens d was 0.35. The protocol demonstrated a very good level of reliability. We present a novel and reliable preloaded time-trial protocol that more closely reflects operational activities and can be used to quantify load carriage performance. This protocol provides greater ecologically validity regarding physical demands of load carriage activities than those adopted previously and provides an excellent tool for the strength and conditioning practitioner to assess individual load carriage performance.

Influence of hydration volume and ambient temperature on physiological responses while wearing CBRN protective clothing

This study examined a low (L; 5 ml/kg per h) and high (H, 10 ml/kg per h) rate of fluid replacement in moderate (18°C) and hot (30°C) conditions on physiological responses while wearing personal protective equipment (PPE). PPE included the gas-tight suit (GTS), the powered respirator protective suit (PRPS) and the civil responder 1 (CR1). Relative to the moderate condition, physiological responses were greater in the hot condition. The percentage change in body mass was different (p < 0.05) between L and H in the hot (L vs. H, GTS: −0.83 vs. −0.38%; PRPS: −1.18 vs. −0.71%; CR1: −1.62 vs. −0.57%) and moderate conditions, although in GTS and CR1 body mass increased (L vs. H, GTS: −0.48 vs. 0.06%; PRPS: −0.66 vs. −0.11%; CR1: −0.18 vs. 0.67%). Fluid replacement strategies for PPE should be adjusted for environmental conditions in order to avoid >1% body mass loss and/or net body mass gain. Statement of Relevance:Currently, the UK Emergency Services do not have specific evidence-based fluid replacement guidelines to follow when wearing chemical, biological, radiological and/or nuclear (CBRN) PPE. Although ad libitum fluid replacement is encouraged (when breathing apparatus permits), recommendations from evidence-based findings specific to different PPE and to different environmental conditions are lacking. This study provides novel evidence supporting the need to develop fluid replacement strategies during CBRN deployments in both moderate and hot environmental conditions for CBRN PPE.

Training the inspiratory muscles improves running performance when carrying a 25 kg thoracic load in a backpack.

Abstract Load carriage (LC) exercise in physically demanding occupations is typically characterised by periods of low-intensity steady-state exercise and short duration, high-intensity exercise while carrying an external mass in a backpack; this form of exercise is also known as LC exercise. This induces inspiratory muscle fatigue and reduces whole-body performance. Accordingly we investigated the effect of inspiratory muscle training (IMT, 50% maximal inspiratory muscle pressure (PImax) twice daily for six week) upon running time-trial performance with thoracic LC. Nineteen healthy males formed a pressure threshold IMT (n = 10) or placebo control group (PLA; n = 9) and performed 60 min LC exercise (6.5 km h–1) followed by a 2.4 km running time trial (LCTT) either side of a double-blind six week intervention. Prior to the intervention, PImax was reduced relative to baseline, post-LC and post-LCTT in both groups (pooled data: 13 ± 7% and 16 ± 8%, respectively, p < .05) and similar changes were observed post-PLA. Post-IMT only, resting PImax increased +31% (p < .05) and relative to pre-IMT was greater post-LC (+19%) and post-LCTT (+18%, p < .05), however, the relative reduction in PImax at each time point was unchanged (13 ± 11% and 17 ± 9%, respectively, p > .05). In IMT only, heart rate and perceptual responses were reduced post-LC (p < .05). Time-trial performance was unchanged post-PLA and improved 8 ± 4% after IMT (p < .05). In summary, when wearing a 25 kg backpack, IMT attenuated the cardiovascular and perceptual responses to steady-state exercise and improved high-intensity time-trial performance which we attribute in part to reduced relative work intensity of the inspiratory muscles due to improved inspiratory muscle strength. These findings have real-world implications for occupational contexts.

Effects of load mass carried in a backpack upon respiratory muscle fatigue.

Abstract Purpose: The purpose of this study was to investigate whether loads carried in a backpack, with a load mass ranging from 0 to 20 kg, causes respiratory muscle fatigue. Methods: Eight males performed four randomised load carriage (LC) trials comprising 60 min walking at 6.5 km h−1 wearing a backpack of either 0 (LC0), 10 (LC10), 15 (LC15) or 20 kg (LC20). Inspiratory (PImax) and expiratory (PEmax) mouth pressures were assessed prior to and immediately following each trial. Pulmonary gas exchange, heart rate (HR), blood lactate and glucose concentration and perceptual responses were recorded during the first and final 60 s of each trial. Results: Group mean PImax and PEmax were unchanged following 60-min load carriage in all conditions (p > .05). There was an increase over time in pulmonary gas exchange, HR and perceptions of effort relative to baseline measures during each trial (p < .05) with changes not different between trials (p > .05). Conclusions: These findings indicate that sub-maximal walking with no load or carrying 10, 15 or 20 kg in a backpack for up to 60 min does not cause respiratory muscle fatigue despite causing an increase in physiological, metabolic and perceptual parameters.

Whole-body active warm-up and inspiratory muscle warm-up do not improve running performance when carrying thoracic loads

Whole-body active warm-ups (AWU) and inspiratory muscle warm-up (IMW) prior to exercise improves performance on some endurance exercise tasks. This study investigated the effects of AWU with and without IMW upon 2.4-km running time-trial performance while carrying a 25-kg backpack, a common task and backpack load in physically demanding occupations. Participants (n = 9) performed five 2.4-km running time-trials with a 25-kg thoracic load preceded in random order by (i) IMW comprising 2 × 30 inspiratory efforts against a pressure-threshold load of 40% maximal inspiratory pressure (PImax), (ii) 10-min unloaded running (AWU) at lactate turnpoint (10.33 ± 1.58 km·h-1), (iii) placebo IMW (PLA) comprising 5-min breathing using a sham device, (iv) AWU+IMW, and (v) AWU+PLA. Pooled baseline PImax was similar between trials and increased by 7% and 6% following IMW and AWU+IMW (P < 0.05). Relative to baseline, pooled PImax was reduced by 9% after the time-trial, which was not different between trials (P > 0.05). Time-trial performance was not different between any trials. Whole-body AWU and IMW performed alone or combination have no ergogenic effect upon high-intensity, short-duration performance when carrying a 25-kg load in a backpack.

Impact of weekly swimming training distance on the ergogenicity of inspiratory muscle training in well trained youth swimmers.

Lomax, M, Kapus, J, Brown, PI, and Faghy, M. Impact of weekly swimming training distance on the ergogenicity of inspiratory muscle training in well-trained youth swimmers. J Strength Cond Res 33(8): 2185-2193, 2019-The aim of this study was to examine the impact of weekly swimming training distance on the ergogenicity of inspiratory muscle training (IMT). Thirty-three youth swimmers were recruited and separated into a LOW and HIGH group based on weekly training distance (≤31 km·wk and >41 km·wk, respectively). The LOW and HIGH groups were further subdivided into control and IMT groups for a 6-week IMT intervention giving a total of 4 groups: LOWcon, LOWIMT, HIGHcon, and HIGHIMT. Before and after the intervention period, swimmers completed maximal effort 100- and 200-m front crawl swims, with maximal inspiratory and expiratory mouth pressures (PImax and PEmax, respectively) assessed before and after each swim. Inspiratory muscle training increased PImax (but not PEmax) by 36% in LOWIMT and HIGHIMT groups (p ≤ 0.05), but 100- and 200-m swims were faster only in the LOWIMT group (3 and 7% respectively, p ≤ 0.05). Performance benefits only occurred in those training up to 31 km·wk and indicate that the ergogenicity of IMT is affected by weekly training distance. Consequently, training distances are important considerations, among others, when deciding whether or not to supplement swimming training with IMT.