Gregory E Peoples

Fish oil reduces heart rate and oxygen consumption during exercise

Dietary omega-3 polyunsaturated fatty acids (PUFAs) are readily incorporated into heart and skeletal muscle membranes where, in the heart, animal studies show they reduce O2 consumption. To test the hypothesis that omega-3 PUFAs alter O2 efficiency in humans, the effects of fish oil (FO) supplementation on O2 consumption during exercise were evaluated. Sixteen well-trained men (cyclists), randomly assigned to receive 8 × 1 g capsules per day of olive oil (control) or FO for 8 weeks in a double-blind, parallel design, completed the study (control: n = 7, age 27.1 ± 2.7 years; FO: n = 9, age 23.2 ± 1.2 years). Subjects used an electronically braked cycle ergometer to complete peak O2 consumption tests (VO2peak) and sustained submaximal exercise tests at 55% of peak workload (from the VO2peak test) before and after supplementation. Whole-body O2 consumption and indirect measurements of myocardial O2 consumption [heart rate and rate pressure product (RPP)] were assessed. FO supplementation increased omega-3 PUFA content of erythrocyte cell membranes. There were no differences in VO2peak (mL kg−1 min−1) (control: pre 66.8 ± 2.4, post 67.2 ± 2.3; FO: pre 68.3 ± 1.4, post 67.2 ± 1.2) or peak workload after supplementation. The FO supplementation lowered heart rate (including peak heart rate) during incremental workloads to exhaustion (P < 0.05). In addition, the FO supplementation lowered steady-state submaximal exercise heart rate, whole-body O2 consumption, and RPP (P < 0.01). Time to voluntary fatigue was not altered by FO supplementation. This study indicates that FOs may act within the healthy heart and skeletal muscle to reduce both whole-body and myocardial O2 demand during exercise, without a decrement in performance.

Upward and downward physical appearance comparisons: Development of scales and examination of predictive qualities

Despite good theoretical and empirical rationale for assessing tendencies to make upward and downward physical appearance comparisons no measure for these specific constructs exists. The present work developed and tested the psychometric properties of upward and downward physical appearance comparison scales. The scales were administered to participants (N=224) along with measures of general appearance comparison tendencies, body image, disordered eating, Antifat and Antigay attitudes. The scales displayed good psychometric properties. Importantly, the upward but not downward physical appearance comparison scale predicted lower Appearance Evaluation and higher EAT-26 scores. Conversely, the downward but not upward physical appearance comparison scale predicted higher Appearance Evaluation and greater Antifat Attitudes (Dislike). The scales were unrelated to a nonappearance related construct. These new measures fill a gap in the literature and may be of benefit to researchers interested in body image, appearance concerns, eating disorders, social comparison, and obesity prejudice.

Dietary fish oil reduces skeletal muscle oxygen consumption, provides fatigue resistance and improves contractile recovery in the rat in vivo hindlimb.

Dietary fish oil modulates skeletal muscle membrane fatty acid composition. Similar changes in heart membrane composition modulate myocardial oxygen consumption and enhance mechanical performance. The rat in vivo autologous perfused hindlimb was used to investigate the influence of membrane composition on skeletal muscle function. Male Wistar rats were fed either saturated fat (SF), n-6 PUFA (linoleic acid rich) or n-3 PUFA (fish oil) diets for 8 weeks. Hindlimb skeletal muscle perfused using the animals own blood was stimulated via the sciatic nerve (1 Hz, 6-12 V, 0·05 ms) to contract in repeated 10 min bouts. The n-3 PUFA diet markedly increased 22 : 6n-3 DHA, total n-3 PUFA and decreased the n-6:n-3 PUFA ratio (P < 0·05) in red and white skeletal muscle membranes. There was no difference in initial twitch tension but the n-3 PUFA group maintained greater twitch tension within all contraction bouts and recovered better during rest to produce greater twitch tension throughout the final contraction bout (P < 0·05). Hindlimb oxygen consumption during contraction was significantly lower in the n-3 PUFA group compared with the SF group, producing a significantly higher O₂ efficiency index compared with both SF and n-6 PUFA groups (P < 0·05). Resting oxygen consumption was increased in recovery in the SF group (P < 0·05) but did not change in the n-3 PUFA group. Membrane incorporation of n-3 PUFA DHA following fish oil feeding was associated with increased efficiency of muscle O₂ consumption and promoted resistance to muscle fatigue.

Load carriage, human performance, and employment standards

The focus of this review is on the physiological considerations necessary for developing employment standards within occupations that have a heavy reliance on load carriage. Employees within military, fire fighting, law enforcement, and search and rescue occupations regularly work with heavy loads. For example, soldiers often carry loads >50 kg, whilst structural firefighters wear 20-25 kg of protective clothing and equipment, in addition to carrying external loads. It has long been known that heavy loads modify gait, mobility, metabolic rate, and efficiency, while concurrently elevating the risk of muscle fatigue and injury. In addition, load carriage often occurs within environmentally stressful conditions, with protective ensembles adding to the thermal burden of the workplace. Indeed, physiological strain relates not just to the mass and dimensions of carried objects, but to how those loads are positioned on and around the body. Yet heavy loads must be borne by men and women of varying body size, and with the expectation that operational capability will not be impinged. This presents a recruitment conundrum. How do employers identify capable and injury-resistant individuals while simultaneously avoiding discriminatory selection practices? In this communication, the relevant metabolic, cardiopulmonary, and thermoregulatory consequences of loaded work are reviewed, along with concomitant impediments to physical endurance and mobility. Also emphasised is the importance of including occupation-specific clothing, protective equipment, and loads during work-performance testing. Finally, recommendations are presented for how to address these issues when evaluating readiness for duty.

Intrinsic heart rate recovery after dynamic exercise is improved with an increased omega-3 index in healthy males

Dietary fish consumption contributes to a reduced risk of cardiac mortality. In the present study, the effect of low-dose fish oil (FO) supplementation on heart rate (HR) response to intense exercise and recovery was investigated in physically fit males. The subjects (n 26) were supplemented (double-blind, parallel design) with (2 × 1 g/d) soya bean oil (control) or tuna FO providing the long-chain n-3 PUFA DHA (560 mg) and EPA (140 mg). Erythrocyte omega-3 index (%EPA+DHA), HR, HR variability and HR recovery were analysed during rest, intense exercise and recovery at baseline and after 8 weeks of supplementation. The mean erythrocyte omega-3 index, which did not differ between the groups at baseline (control 4.2 (sem 0.2), n 13; FO 4.7 (sem 0.2), n 13), remained unchanged in the control group (3.9 (sem 0.2)), but increased in the FO group (6.3 (sem 0.3); P< 0.01). The mean HR during supine resting conditions (control 56 (sem 10); FO 59 (sem 9)) was not affected by FO supplementation. Poincaré analysis of HR variability at rest exhibited a decreasing trend in parasympathetic activity in the FO group (SD1 (standard deviation of points perpendicular to the axis of line of identity)/SD2 (standard deviation of points along the axis of line of identity): control 0.02 (sem 0.01); FO - 0.05 (sem 0.02); P= 0.18). Peak HR was not affected by supplementation. However, during submaximal exercise over 5 min, fewer total heart beats were recorded in the FO group (-22 (sem 6) ( = -4.5 beats/min)), but not in the control group (+1 (sem 4)) (P< 0.05). Supine HR recovery (half-time) after cycling was significantly faster after FO supplementation (control - 0.4 (sem 1.2) s; FO - 8.0 (sem 1.7) s; P< 0.05). A low intake of FO increased the omega-3 index and reduced the mean exercise HR and improved HR recovery without compromising the peak HR. A direct influence of DHA via reductions in the cardiac intrinsic beat rate was balanced by a reciprocal decrease in vagal tone.

Muscle fatigue resistance in the rat hindlimb in vivo from low dietary intakes of tuna fish oil that selectively increase phospholipid n -3 docosahexaenoic acid according to muscle fibre type

Dietary fish oil (FO) modulates muscle O2 consumption and contractile function, predictive of effects on muscle fatigue. High doses unattainable through human diet and muscle stimulation parameters used engender uncertainty in their physiological relevance. We tested the hypothesis that nutritionally relevant FO doses can modulate membrane fatty acid composition and muscle fatigue. Male Sprague-Dawley rats were randomised to control (10% olive oil (OO) by weight) or low or moderate FO diet (LowFO and ModFO) (HiDHA tuna fish oil) for 15 weeks (LowFO: 0.3% FO, 9.7% OO, 0.25% energy as EPA+DHA; ModFO: 1.25% FO, 8.75% OO, 1.0% energy as EPA+DHA). Hindlimb muscle function was assessed under anaesthesia in vivo using repetitive 5 s burst sciatic nerve stimulation (0.05 ms, 7-12 V, 5 Hz, 10 s duty cycle, 300 s). There were no dietary differences in maximum developed muscle force. Repetitive peak developed force fell to 50% within 62 (SEM 10) s in controls and took longer to decline in FO-fed rats (LowFO 110 (SEM 15) s; ModFO 117 (sem 14) s) (P<0.05). Force within bursts was better sustained with FO and maximum rates of force development and relaxation declined more slowly. The FO-fed rats incorporated higher muscle phospholipid DHA-relative percentages than controls (P<0.001). Incorporation of DHA was greater in the fast-twitch gastrocnemius (Control 9.3 (SEM 0.8) %, LowFO 19.9 (SEM 0.4), ModFO 24.3 (SEM 1.0)) than in the slow-twitch soleus muscle (Control 5.1 (SEM 0.2), LowFO 14.3 (SEM 0.7), ModFO 18.0 (SEM 1.4)) (P<0.001), which was comparable with the myocardium, in line with muscle fibre characteristics. The LowFO and ModFO diets, emulating human dietary and therapeutic supplement intake, respectively, both elicited muscle membrane DHA enrichment and fatigue resistance, providing a foundation for translating these physiological effects to humans.

Revisiting Ventilatory and Cardiovascular Predictions of Whole-Body Metabolic Rate

Objective: The influence of variations in exercise mode, thermal state, and load carriage on cardiac and ventilatory predictors of metabolic rate were investigated. Methods: Fifteen males were studied at rest and during whole-, upper-, and lower-body exercise (unloaded and loaded) under thermoneutral and hot conditions. Results: Ventilatory predictions were superior in thermoneutral (residual mean square error range: 0.04 to 0.17 L·min−1 vs 0.21 to 0.36 L·min−1) and hot conditions (0.03 to 0.07 L·min−1 vs 0.21 to 0.24 L·min−1). Predictions derived from whole- or lower-body exercise, and unloaded or loaded exercise could be interchanged without significant error. Nevertheless, a mode-specific prediction was required for upper-body work, and mild hyperthermia significantly reduced the precision of cardiac predictions. Conclusion: Ventilatory predictions were more precise, but errors from heart-rate predictions could be minimized by using thermal-state and exercise mode-specific predictions.

Effect of interdisciplinary care on weight loss: A randomised controlled trial

Objective To determine the effectiveness of a novel interdisciplinary treatment compared with usual care on weight loss in overweight and obese adult volunteers. Design Single blinded controlled trial. Participants randomly assigned to usual care (C, general guideline-based diet and exercise advice), intervention (I, interdisciplinary protocol) or intervention + a healthy food supplement (30 g walnuts/day) (IW). Setting Community based study, Illawarra region, south of Sydney, Australia. Participants Generally well volunteer adult residents, 25-54 years, body mass index (BMI) 25-40kg/m2 were eligible. At baseline 439 were assessed, 377 were randomised, 298 completed the 3-month intensive phase and 178 completed the 12-month follow-up. Interventions Treatment was provided at clinic visits intensively (0 months, 1 month, 2 months, 3 months) then quarterly to 12 months. Support phone calls were quarterly. All participants underwent blinded assessments for diet, exercise and psychological status. Primary and secondary measures The primary outcome was difference in weight loss between baseline and 12 months (clinically relevant target 5% loss). Secondary outcomes were changes in blood pressure, fasting blood glucose and lipids, and changes in diet, exercise and psychological parameters. Results At 12 months, differences in weight loss were identified (p<0.001). The I group lost more than controls at 3 months (91.11 (92.23,90.00), p<0.05) and the IW more than controls at 3 months (91.25 (92.35,90.15), p<0.05) and 6 months (92.20 (93.90,90.49), p<0.01). The proportion achieving 5% weight loss was significantly different at 3 months, 6 months and 9 months (p=0.04, p=0.03, p=0.03), due to fewer controls on target at 3 months, 6 months and 9 months and more IW participants at 6 months. Reductions in secondary outcomes (systolic blood pressure, blood glucose/lipid parameters and lifestyle measures) followed the pattern of weight loss. Conclusions An interdisciplinary intervention produced greater and more clinically significant and sustained weight loss compared with usual care. The intensive phase was sufficient to reach clinically relevant targets, but long-term management plans may be required. Trial registration number ANZCTRN 12614000581662; Post-results.

Balancing ballistic protection against physiological strain: evidence from laboratory and field trials

This project was based on the premise that decisions concerning the ballistic protection provided to defence personnel should derive from an evaluation of the balance between protection level and its impact on physiological function, mobility, and operational capability. Civilians and soldiers participated in laboratory- and field-based studies in which ensembles providing five levels of ballistic protection were evaluated, each with progressive increases in protection, mass (3.4-11.0 kg), and surface-area coverage (0.25-0.52 m(2)). Physiological trials were conducted on volunteers (N = 8) in a laboratory, under hot-dry conditions simulating an urban patrol: walking at 4 km·h(-1) (90 min) and 6 km·h(-1) (30 min or to fatigue). Field-based trials were used to evaluate tactical battlefield movements (mobility) of soldiers (N = 31) under tropical conditions, and across functional tests of power, speed, agility, endurance, and balance. Finally, trials were conducted at a jungle training centre, with soldiers (N = 32) patrolling under tropical conditions (averaging 5 h). In the laboratory, work tolerance was reduced as protection increased, with deep-body temperature climbing relentlessly. However, the protective ensembles could be grouped into two equally stressful categories, each providing a different level of ballistic protection. This outcome was supported during the mobility trials, with the greatest performance decrement evident during fire and movement simulations, as the ensemble mass was increased (-2.12%·kg(-1)). The jungle patrol trials similarly supported this outcome. Therefore, although ballistic protection does increase physiological strain, this research has provided a basis on which to determine how that strain can be balanced against the mission-specific level of required personal protection.

The utility of heart rate and minute ventilation as predictors of whole-body metabolic rate during occupational simulations involving load carriage

The utility of cardiac and ventilatory predictors of metabolic rate derived under temperate and heated laboratory conditions was evaluated during three fire-fighting simulations (70-mm hose drag, Hazmat recovery, bushfire hose drag; N = 16 per simulation). The limits of agreement for cardiac (temperate: − 0.54 to 1.77; heated: − 1.39 to 0.80 l min− 1) and ventilatory surrogates (temperate: − 0.19 to 1.27; heated: − 0.26 to 1.16 l min− 1) revealed an over-estimation of oxygen consumption that exceeded the acceptable limits required by occupational physiologists (N = 25; ± 0.24 l min− 1). Although ventilatory predictions offered superior precision during low-intensity work (P < 0.05), a cardiac prediction was superior during more demanding work (P < 0.05). Deriving those equations under heated conditions failed to improve precision, with the exception of the cardiac surrogate during low-intensity work (P < 0.05). These observations imply that individualised prediction curves are necessary for valid estimations of metabolic demand in the field. Practitioner Summary: Cardiac and ventilatory surrogates are often used to approximate the metabolic demands of work. In this study, however, such predictions demonstrated unsatisfactory agreement with simultaneously measured values across three fire-fighting simulations. Therefore, individually calibrated equations appear necessary to obtain the level of predictive precision required by occupational physiologists.