Ira Jacobs

University of Toronto | U of T · Faculty of Kinesiology and Physical Education

Introduction Diet has an impact on weight status, health, and physical performance. Assessing the usual at-home dietary intakes of military personnel can help ascertain their nutritional status before field training or operations. Preference for foods consumed on a routine basis can also impact the military’s preference for and consumption of field...

Operating in temperature extremes frequently leads to a discrepancy in energy balance. Investigating the effects of operating in extreme cold temperatures on metabolic requirements has not been well described in Canadian Armed Forces (CAF) personnel. The objective was to accurately assess energy deficits using the “gold standard” methodology for me...

Background: Dietary Reference Intakes are used to guide the energy intake of the Canadian Armed Forces (CAF) field rations provided to military personnel deployed for training or operations. However, the high energy expenditures likely to occur under harsh environmental/metabolically challenging deployment conditions may not be adequately consider...

Abstract Background It is not clear whether the frequently reported phenomenon of exercise-induced anorexia is exacerbated or blunted in warm or cold environments. Therefore, this study investigated the effects of exercise in three different environmental temperatures vs. rest, on perceptions of appetite, appetite regulating hormones, and food inta...

The purpose of this study was to clarify if Ratings of Perceived Exertion (RPE) and self-selected exercise intensity are sensitive not only to alterations in the absolute level of arterial saturation (SPO2) but also the rate of change in SPO2. Twelve healthy participants (31.6 ± 3.9 y, 175.5 ± 7.7 cm, 73.3 ± 10.3 kg, 51 ± 7 mL·kg⁻¹·min⁻¹) exercised...

The collection of accurate dietary intakes using traditional dietary assessment methods (e.g., food records) from military personnel is challenging due to the demanding physiological and psychological conditions of training or operations. In addition, these methods are burdensome, time consuming, and prone to measurement errors. Adopting smart-phon...

Exercise- and hypoxia-induced hyperventilation decreases the partial pressure of end-tidal carbon dioxide (PETCO2), which in turn exerts many physiological effects. Several breathing circuits that control PETCO2 have been previously described, but their designs are not satisfactory for exercise studies where changes in inspired oxygen (FIO2) may be...

Surgically implanted continuous flow left ventricular assist devices (CF-LVADs) are currently used in patients with end-stage heart failure (HF). However, CF-LVAD therapy introduces a new set of complications and adverse events in these patients. Major adverse events with the CF-LVAD include right heart failure, vascular dysfunction, stroke, hepati...

Dietary Reference Intakes (DRIs) are the national nutrient requirements designed for the healthy Canadian adult population. They are also used to guide the nutrient content of Canadian Armed Forces (CAF) field rations. These rations are intended to be nutritionally sufficient for standard military operations. However, there is limited data on the a...

Objectives We examine the hypothesis that cyclic guanosine monophosphate (cGMP) levels are elevated in recipients of continuous-flow left ventricular assist devices (CF-LVADs) and that elevated cGMP levels are associated with a risk of gastrointestinal (GI) bleeding events. Methods The levels of cGMP, nitric oxide, platelet activation markers, pla...

Objective: Transdermal delivery of ethinyl estradiol (EE) may be increased in conditions when core body temperature is elevated, such as during exercise. Our aims were to determine the effect of acute aerobic exercise on EE from the transdermal contraceptive patch and examine the correlation between changes in core body temperature and EE. Study de...

The long-term effects of continuous-flow left ventricular assist device (CF-LVAD) support on trends of inflammatory markers over time are unknown. We examined the hypothesis that the levels of inflammatory markers in CF-LVAD recipients are higher than in healthy controls and that these levels increase over time with long-term CF-LVAD support. We ex...

A traditional focus of exercise scientists studying the interaction of drugs and exercise has been on the effects of drugs on exercise performance or functional capacity. In contrast, there is limited information available about the effects of exercise on the efficacy of drugs that have been prescribed and ingested for therapeutic reasons. Those re...

Although the newer continuous flow left ventricular assist devices (CF-LVADs) provide clinical advantages over the pulsatile pumps, the effects of low pulsatility on inflammation are incompletely understood. The objective of our study was to examine the levels of inflammatory mediators in CF-LVAD recipients compared to both healthy controls and to...

This report is a comprehensive review and discussion of relevant existing open-source peer-reviewed literature, government reports, and data. The report provides a basis for future conclusions and recommendations about the nutritional needs of Canadian Armed Forces (CAF) personnel participating in active military field operations, maneuvers or asso...

This study aimed at investigating the relative roles of the duration versus intensity of exercise on the metabolic adaptations in vastus lateralis to short-term (10 day) aerobic-based cycle training. Healthy males with a peak aerobic power ([Formula: see text]) of 46.0 ± 2.0 ml kg(-1) min(-1) were assigned to either a 30-min (n = 7) or a 60-min (n...

This study investigated the hypothesis that the duration of aerobic-based cycle exercise would affect the adaptations in substrate and metabolic regulation that occur in vastus lateralis in response to a short-term (10 day) training program. Healthy active but untrained males (n = 7) with a peak aerobic power ([Formula: see text]) of 44.4 ± 1.4 ml...

The Directorate Armament Sustainment Programme Management (DASPM) requested Defence R&D Canada (DRDC) support with the investigation and recommendation of "...technologies available to mitigate the effects of the heat stress expected for Leopard 2C crews operating in the Kandahar region of Afghanistan in summer." DRDC was asked to focus "...on tech...

Defence R&D Canada (DRDC) is embarking on a central initiative to develop a comprehensive infrastructure strategy. A major objective of the initiative is to identify and justify the infrastructure required by DRDC to ensure that it remains a world leader in its Science & Technology activities. The strategy will include addressing issues such as the...

Although Canadian Forces (CF) efforts directed at developing new G-protection strategies have often raised the question of potential benefits of physical conditioning (PC) on G tolerance (GT), a fatality in a CF fighter aircraft accident, in which it was suggested the pilot may have had 'sub-optimal GT,' sparked renewed interest in this topic. A tw...

The stimulant modafinil has proved to be an effective treatment modality for narcolepsy and related sleep disorders and is also being studied for use during sustained military operations to ameliorate the effects of fatigue due to sleep loss. However, a previous study reported that a relatively large, single dose of modafinil (300 mg), administered...

The purpose of this study was to investigate the effect of acute ingestion of modafinil (M) on time to exhaustion during high-intensity exercise. Modafinil (M) is a psychostimulant developed to treat narcolepsy, with "arousal" properties attributed to an increased release of dopamine in the CNS. Because other stimulants with similar properties have...

The purpose of this study was to investigate the effects of ingesting caffeine (C), ephedrine (E), and their combination on muscular endurance, using a double-blind, repeated measures design. Ninety minutes after ingesting either C (4 mg x kg-1), E (0.8 mg x kg-1), a combination of C+E, or a placebo (P), 13 male subjects performed a weight-training...

Ingestion of a combination of caffeine (C) and ephedrine (E) prolongs time to exhaustion during high-intensity aerobic exercise. CNS stimulation by C and E was proposed as part of the mechanism for the improvement. It was thought that this arousal might also be of benefit during anaerobic exercise. The purpose of this study was to investigate the e...

Eleven women (age = 24.4 +/- 6.3 yr, mass = 65.0 +/- 7.8 kg, height = 167 +/- 8 cm, body fatness = 22.4 +/- 5.9%, mean +/- SD) were immersed to neck level in 18 degrees C water for up to 90 min for comparison of their thermal responses with those of men (n = 14) in a previous similarly conducted protocol. Metabolic rate increased about three times...

Ingestion of a combination of 5 mg x kg(-1) caffeine (C), and 1 mg x kg(-1) ephedrine (E) was reported to have an ergogenic effect on high intensity aerobic exercise performance, but 25% of the subjects experienced vomiting and nausea while engaging in hard exercise after the treatment. The present study was undertaken to investigate whether reduce...

This paper summarizes and interprets the research published about physiological aspects of dietary supplementation with creatine monohydrate and the effects on physical performance. A nitrogenous molecule that occurs naturally in the flesh consumed by meat-eaters, creatine is also synthesized endogenously and is stored primarily in skeletal muscle....

Dietary creatine (Cr) supplementation is currently a common practice among athletes and U.S. Naval Special Warfare personnel. The ergogenic effect of supplemental Or has been demonstrated under certain well-controlled laboratory conditions, but the evidence supporting Cr use to augment performance under operational or field conditions is equivocal....

The ingestion of a combination of caffeine and ephedrine has an ergogenic effect on physical performance. Before recommending tactical applications of such a treatment the health risks must be determined. Therefore, it was the purpose of this study to clarify the effects of an acute ingestion of caffeine, ephedrine and their combination on heart ra...

Ingesting a combination of caffeine and ephedrine (C+E) has been shown to raise metabolic heat production and body temperature. This side effect of C+E ingestion may be positive during a cold stress scenario, however, during heat stress it could prove to be detrimental. Thus, the purpose of this study was to clarify the effect of C+E ingestion on b...

The ingestion of a combination of caffeine (C) and ephedrine (E) has been reported to prolong exercise time to exhaustion during cycle ergometry at 85% VO2max. The present study was undertaken to investigate whether this enhancement would occur in a field setting and if drug ingestion on 1 d would affect performance 1 d later. Two hours after inges...

Thirteen healthy and fit men [age = 27 +/- 8 (SD) yr, height = 177 +/- 5 cm, mass = 75 +/- 7 kg, body fat = 14 +/- 5%, maximal O2 consumption = 51 +/- 4 ml. kg-1. min-1] participated in an experiment designed to test their thermoregulatory response to a challenging cold exposure after 5 h of demanding mixed exercise during which only water was cons...

To characterize the important changes in the selection and mobilization of metabolic fuel during cold stress, six males rested for 3 h at 29 degrees C and at 5 degrees C dressed only in shorts while 2H5 glycerol, 1-13C palmitate and 6,6 2H2 glucose were continuously infused for 3 h in each condition to determine their rate of turnover (Ra). Metabol...

This study investigated the effects of acute ingestion of caffeine (C), ephedrine (E) and their combination (C+E) on time to exhaustion during high-intensity exercise. Using a repeated-measures, double-blind design, eight male subjects exercised on a cycle ergometer at a power output that led to exhaustion after about 12.6 min during a placebo (P)...

This document is a progress report which describes the results from the first of a series of studies carried out to clarify the extent 6f gender-related differences in physiological responses to cold stress, and to evaluate the potential implications for survival time in the cold. Specifically, this study was designed to clarify the quantity and qu...

The purpose of this study was to test the hypothesis that ingestion of creatine monohydrate increases anaerobic exercise capacity, as reflected by the maximal accumulated oxygen deficit (MAOD). Subjects were assigned, double-blind, to placebo (PL, n = 12) or creatine (CR, n = 14) groups and ingested 5-g doses 4 times daily of artificial sweetener o...

This study tested the hypothesis that respiratory muscle fatigue occurs during a simulated air combat maneuver (SACM) centrifuge profile. Six subjects (four males, two females) were exposed to a SACM consisting of alternating +4 Gz to +7 Gz plateaus until volitional fatigue. Electrical activities of the diaphragm, scalene, intercostal and external...

The purpose of this study was to examine the effects of ginseng extract ingestion on physiological responses to intense exercise. Subjects performed a control ride (CN) on a cycle ergometer, followed by placebo (PL) and ginseng (GS) treatments. Ginseng was ingested as 8 or 16 mg/kg body weight daily for 7 days prior to trial GS. Venous blood was sa...

The effects of carbohydrate (CHO) loading on physical characteristics including muscle fiber distribution, muscle glycogen concentration, and physical performance were studied in two top Swedish ice hockey teams. Players were randomly allocated to two groups: those consuming a CHO-enriched diet (CHO group) and those consuming a mixed diet (controls...

Managing alertness of soldiers during sustained operations is a source of serious concern for military unit commanders. A frequently employed strategy is to induce sleep before an operation, especially operations requiring prolonged travel. Sleep-inducing drugs could have an action on thermoregulation through their effect on alertness and a possibl...

To clarify the source of increased carbohydrate oxidation during cold stress, six males rested for 3 h at 29 and 10 degrees C dressed only in shorts. After priming the blood glucose and bicarbonate pools, [U-13C6]glucose was infused for 3 h in each condition to determine the plasma glucose rate of appearance (Ra) or turnover under relative steady-s...

Exercise time to exhaustion (TE) is commonly used to evaluate the success or failure of such treatments as endurance training programs or nutritional supplements. The present study determined the variability of TE during submaximal exercise at 80% VO2max. Fifteen males performed cycle exercise to exhaustion on five occasions at the same time of day...

This study tested the hypothesis that repeated exposure to high levels of +Gz acceleration, in conjunction with repeated execution of an Anti-G Straining Maneuver (AGSM), causes central fatigue, presumably by impairing central nervous system (CNS) function. We speculated that central fatigue would impair the ability to recruit sufficient musculatur...

Military personnel often undergo sustained operations that affect vigilance and alertness. Pharmacological agents may be used to enhance vigilance. Most such agents also have thermogenic properties. Whether a new promising stimulant, modafinil (Lyons and French, Aviat. Space Environ. Med. 1991; 62:432-435), has a beneficial effect on cold tolerance...

SEALS must optimize physical training "efficiency" i.e., adaptation per unit training time. This study was designed to determine if a single training program could simultaneously elicit aerobic and anaerobic adaptations. SEALs were assigned to groups matched for initial aerobic and anaerobic fitness. Each group trained on cycle ergometers for 30 mi...

Military personnel can be exposed to emergency survival conditions in cold environments which could result in lethal levels of hypothermia if appropriate insulation or protective shelters are not available. Hypothermia can be delayed in humans if metabolic heat production is increased, and we have previously demonstrated that pretreatment with cert...

Pilots exposed to high levels of headward (+Gz) acceleration must perform voluntary muscle contractions in order to maintain head-level arterial pressure. To study the possibility that muscular fatigue can limit human +Gz duration tolerance, electromyographic (EMG) activity and EMG indices of muscular fatigue were measured during a simulated air co...

It is hypothesized that our inability to confirm that energy substrate mobilization is a limiting factor for cold-induced thermogenesis (M) in humans (1, 2) is due to a sub-optimal dose of ingested substrates. This hypothesis was tested in healthy males exposed twice to the cold (3h at 7°C, 1 m.s−1 wind, nude, fasting) following the ingestion of ei...

To investigate the adequacy of food rations to supply energy needs in cold-temperature environments, caloric expenditure and intake and body composition changes were measured in a group of infantrymen during a 10-day field exercise in the Canadian Arctic. Energy expenditure was measured by the doubly labeled water method (n = 10), and caloric intak...

The individual anaerobic threshold (IAT) has received attention recently in the field of exercise physiology. The IAT is defined as the point during progressive exercise when lactate elimination from the blood is both maximal and equal to the diffusion from the working muscles. It has been theorized that an individual can maintain exercise for rela...

This study examined the effects of environmental temperature and metabolic rate on soldiers' work tolerance time (WTT) while wearing various levels of nuclear, biological, and chemical (NBC) defence protective clothing. There were 23 unacclimatized males (23 +/- 3 years, 76 +/- 8 kg, 1.77 +/- 0.08 m) assigned to exercise at either a light (walking...

This study examined the benefits of work and rest schedules on soldiers' work tolerance (WTT) while wearing various levels of nuclear, biological and chemical (NBC) defence protective clothing in a warm environment (30 degrees C and 50% R.H.). Eight unacclimatized males were assigned to exercise at either a light (walking 1.11 m.s-1 0% grade, alter...

Previous studies linked muscular fatigue with a decrease in blood pH. This study investigated if the means of altering pH affected the extent of muscular fatigue. Drug-induced and exercise-induced acidosis were compared to test the hypothesis that exercise-induced acidosis impairs subsequent muscular performance more than chemically induced acidosi...

In previous studies, we have not been able to confirm the theory that energy substrate mobilization is a limiting factor for cold-induced thermogenesis (M) in humans. One possible explanation for the conflicting results is that the dose of energy substrates may not have been optimal. The goal of this study was to determine whether the ingestion of...

Energy substrate mobilization has been suggested as being a limiting factor for the rate of cold-induced thermogenesis (M), and consequently in delaying hypothermia. The evidence supporting this hypothesis in humans, however, is not convincing and the hypothesis has yet to be tested in a rigorous manner using a full heat balance analysis (partition...

The individual anaerobic threshold (IAT) has been defined as the highest metabolic rate at which blood lactate (La) concentrations are maintained at a steady state during prolonged exercise. The validity of this definition, however, has not been substantiated. Eleven men [maximum oxygen uptake (VO2max), mean (SD), 57.8 (6.9) ml.kg-1 x min-1) did tw...

In a recent study, we have shown that the commercially available Cold Buster(TM) Sports bar, purported to improve cold resistance, did not do so in our subjects exposed to a relatively severe cold test. (Vallerand, Tikuisis, Ducharme and Jacobs, In Review). One possible explanation for our conflicting results is that our metabolic rate (M) was too...

Recent advances on the influence of cold exposure on energy metabolism in animals and humans are summarized. Although the cold-induced enhancements in carbohydrate metabolism have been the focus of numerous studies, it was only recently that pieces of evidence from animal studies have suggested that cold exposure exerts an insulin-like effect on pe...

The intensity of cold-induced shivering, quantified by surface electromyography (EMG) and then expressed as a function of the maximal myoelectrical activity (integrated EMG) obtained during a maximum voluntary contraction (MVC), was examined in this study in individuals classified by body fat. In addition, the relationship between shivering and met...

Muscle glycogen and muscle and blood lactate were evaluated before and after a +4.0/7.0 Gz simulated air combat maneuvering (SACM) protocol in the human centrifuge. The subjects were eight healthy males, ages 25-43 years. Muscle glycogen and lactate were determined from biopsies of m. vastus lateralis in six subjects and whole blood lactate was ana...

The individual anaerobic threshold (Th(an)) is the highest metabolic rate at which blood lactate concentrations can be maintained at a steady-state during prolonged exercise. The purpose of this study was to test the hypothesis that training at the Th(an) would cause a greater change in indicators of training adaptation than would training "around"...

This study evaluated the blood lactate concentration ([LA-]) response to the Canadian Aerobic Fitness Test (CAFT) in female subjects and compared the strength of prediction of VO2max determined by [LA-] and heart rate (HR). The sample was composed of 98 Canadian Forces females between the ages of 18 and 45 years. The [LA-] after each stage of the s...

Thirty-eight Navy SEALs performed aerobic fitness and maximal anaerobic capacity tests on a cycle ergometer. Lactic acid concentration was measured in blood samples taken during the aerobic fitness test. After recording prior dietary intake and physical activity, thirty-six subjects had biopsies taken from the vastus lateralis muscle. Biopsy result...

This study evaluated the blood lactate (LA) response to stepping exercise, specifically the Canadian Aerobic Fitness Test (CAFT). It also compared the correlation between either LA or heart rate (HR) at a given stage of the CAFT and directly measured maximal aerobic power (VO2max). A total of 137 male Canadian Forces (CF) personnel between the ages...

This study investigated the effects of many years of bodybuilding on muscular strength and endurance. Eight bodybuilders (BB), 4 males and 4 females, and 8 controls (C), 4 males and 4 females, performed a muscle fatigue test (MFT) consisting of 25 maximal leg extensions at angular velocities of 180 and 300 degrees/s. The results for strength showed...

The purpose of this study was to investigate whether simultaneous alterations in the availability of plasma free fatty acids and muscle glycogen would impair the maintenance of thermal balance during cold water immersion in humans. Eight seminude subjects were immersed on two occasions in 18 degrees C water for 90 min or until rectal temperature (T...

The Canadian Forces (CF) personnel have their fitness measured by the EXPRESS test. This test includes measures of strength, muscular endurance, aerobic power and body composition. Of the performance measures i.e., strength, muscular endurance and aerobic power, the first two are measured directly while the last is predicted or estimated from heart...

The onset and intensity of shivering of various muscles during cold air exposure are quantified and related to increases in metabolic rate and convective heat loss. Thirteen male subjects resting in a supine position and wearing only shorts were exposed to 10 degrees C air (42% relative humidity and less than 0.4 m/s airflow) for 2 h. Measurements...

The individual anaerobic threshold (IAT) is defined as the highest metabolic rate at which blood lactate (LA) concentrations are maintained at a steady-state during prolonged exercise. The purpose of this study was to compare the effects of active and passive recovery on the determination of IAT following both a submaximal or maximal incremental ex...

Previous research has shown that the rate of muscle glycogen utilization is related to exercise intensity expressed relative to maximal aerobic power (%VO2max). The purpose of this study was to compare the relationship between glycogen utilization and %VO2max to that between glycogen utilization and intensity expressed relative to the onset of bloo...

Recent human studies have shown that cold exposure increases lipid oxidation, even when the oxidation of circulating free fatty acid (FFA) is markedly reduced by the ingestion of nicotinic acid, thus seriously questioning the importance of FFA for lipid oxidation in the cold-exposed humans. It was therefore hypothesized that similarly to prolonged...

Fifteen male physical education students were studied. The subjects trained for 4-6 weeks, 2-3 days per week, on a mechanically braked bicycle ergometer. A training session consisted of repeated 30-s 'all-out' sprints on a Wingate bicycle ergometer, on which the brake band of the flywheel was loaded with 75 g kg-1 body wt, with rest periods of 15-2...

Endurance capacity of human vastus lateralis muscles was observed 24 h after hard exercise followed by either a carbohydrate-restricted or a carbohydrate-loaded diet (depletion and repletion conditions). In a control condition the subjects did no previous exercise and ate their normal diet. Each of these conditions was followed by an experimental p...

Canadian Forces personnel must be able to sustain operations in an environment contaminated with nuclear, biological and/or chemical (NBC) agents. Clothing has been designed that protects the individual from a hostile NBC environment. This clothing, however, impairs body heat loss. The degree of impairment is magnified if metabolic heat production...

The effects of long-term strength training on skeletal muscle fibre characteristics were evaluated in nine body builders (BB) (five males and four females) and ten control subjects (six females and four males). Muscle fibre area, percentage fibre type, and capillary supply were compared between the BB and controls as well as between the males and f...

To compare the responses to doing strength (S) training on alternate days with endurance (E) training vs doing both types of training on the same days per week, seven young men (group A-2 d) did S and E training together in single sessions 2 d.wk-1 for 20 wk. A second group (B-4 d, N = 8) did the S training on 2 d.wk-1 and E training on 2 other d.w...