Thomas B. Walker

Lessons from the War on Dietary Fat

Conventional dietary guidelines put forth by health care institutions and providers for the past 40 years have stressed the importance of reducing the amount of dietary fat consumed. Such a diet is purported to mitigate metabolic risk factors and optimize the ability to achieve or maintain a healthy body weight. However, over the past 35 years obesity rates in the United States have risen dramatically though the level of dietary fat consumed by U.S. adults has fallen. This review examines the potential reasons for this paradox. Various meta-analyses, controlled trials, and cohort studies have demonstrated that reducing dietary fat intake provides for very little weight loss unless accompanied by equal or greater reductions in total energy intake. Due to both psychological (e.g., the tendency for people to eat more of what they consider low fat) and physiological (e.g., the low satiety that accompanies carbohydrate intake) factors, reducing total caloric intake while simultaneously reducing fat intake is a difficult challenge. Further, reductions in total carbohydrate intake, increases in protein intake, and adoption of a Mediterranean diet seem to be more effective in inducing weight loss than reductions in fat intake. Traditional claims that simply reducing dietary fat will improve metabolic risk factors are also not borne out by research. There is some evidence that replacing dietary saturated fat with unsaturated fat may improve metabolic risk factors, but that research is not conclusive. Teaching Points: • Over the past 40 years, Americans have decreased the percentage of calories they get from dietary fat while rates of overweight and obesity have risen dramatically. • It appears that a decrease in total dietary fat in ad libitum diets may induce a very small decrease in body weight. • Evidence suggests that reductions in total dietary fat intake often occur in conjunction with an increase in total caloric intake. • It seems reasonable to conclude that guiding the public to simply reduce dietary fat intake is an ineffective method to mitigate the rise in obesity and improve public health.

The Influence of Agility Training on Physiological and Cognitive Performance

Abstract Lennemann, LM, Sidrow, KM, Johnson, EM, Harrison, CR, Vojta, CN, and Walker, TB. The influence of agility training on physiological and cognitive performance. J Strength Cond Res 27(12): 3300–3309, 2013—Agility training (AT) has recently been instituted in several military communities in hopes of improving combat performance and general fitness. The purpose of this study was to determine how substituting AT for traditional military physical training (PT) influences physical and cognitive performance. Forty-one subjects undergoing military technical training were divided randomly into 2 groups for 6 weeks of training. One group participated in standard military PT consisting of calisthenics and running. A second group duplicated the amount of exercise of the first group but used AT as their primary mode of training. Before and after training, subjects completed a physical and cognitive battery of tests including V[Combining Dot Above]O2max, reaction time, Illinois Agility Test, body composition, visual vigilance, dichotic listening, and working memory tests. There were significant improvements within the AT group in V[Combining Dot Above]O2max, Illinois Agility Test, visual vigilance, and continuous memory. There was a significant increase in time-to-exhaustion for the traditional group. We conclude that AT is as effective or more effective as PT in enhancing physical fitness. Further, it is potentially more effective than PT in enhancing specific measures of physical and cognitive performance, such as physical agility, memory, and vigilance. Consequently, we suggest that AT be incorporated into existing military PT programs as a way to improve war-fighter performance. Further, it seems likely that the benefits of AT observed here occur in various other populations.

Acceleration tolerance after ingestion of a commercial energy drink.

BACKGROUND Caffeine ingestion has been demonstrated to increase physical performance in some situations. This study examined the ability of a commercial energy drink containing caffeine to enhance acceleration tolerance and strength under G load. METHODS Eight experienced centrifuge subjects completed three separate experimental acceleration exposures following ingestion of 11.5 ml x kg(-1) bodyweight of (1) a commercial energy drink, providing 5.0 mg caffeine/kg bodyweight; (2) a commercial energy drink without caffeine; or 3) a placebo. The acceleration exposures consisted of a relaxed gradual onset run to peripheral light loss, a rapid onset run to 6 G for 15 s, and a simulated air combat maneuver (SACM) run of repeated alternations between 4.5 G for 15 s and 7 G for 15 s until volitional exhaustion. RESULTS Relaxed G tolerance was 13% higher under the caffeinated energy drink session, whereas SACM duration did not differ among the drink conditions. Hip adductor muscle strength was 37% lower during the placebo session than during the other two sessions. CONCLUSION Consumption of a caffeine-based energy drink may enhance relaxed G tolerance and may increase strength, but does not impact acceleration tolerance duration.

Is performance of intermittent intense exercise enhanced by use of a commercial palm cooling device

Walker, TB, Zupan, MF, McGregor, JN, Cantwell, AR, and Norris, TD. Performance of intermittent intense exercise enhanced by use of a commercial palm cooling device? J Strength Cond Res 23(9): 2666-2672, 2009-The purpose of this study was to determine if using the CoreControl Rapid Thermal Exchange (RTX), a commercial palm cooling device, during active rest periods of multiple set training is an effective means to increase performance. Ten volunteers (5 men, 5 women) completed a &OV0312;o2max test on a motorized treadmill and 3 interval running tests on a human powered treadmill. This treadmill allowed the subjects to quickly reach their running speed while allowing for measurement of distance, speed, and force. During the interval running tests the subjects completed eight 30-second intervals at a hard/fast pace followed by a 90-second walking or light jogging recovery period. During the recovery period, the subjects placed their left hand on 1 of 3 media: the RTX held at 15°C (R), a 15°C standard refrigerant gel pack (P), or nothing at all (C). Although there were differences in core temperature (Tc), subjective heat stress ratings, distance, and power generated between intervals, there were no significant differences (p < 0.05) found between treatments for any of these variables, nor was the interaction effect of interval*treatment found to be significant. Mean distance completed per trial was 717.1 m ± 124.4 m (R), 724.8 m ± 130.3 m (P), and 728.6 m ± 110.6 m (C). Change in Tc from baseline to end-test averaged 1.41°C ± 0.37°C (R), 1.41°C ± 0.39°C (P), and 1.41°C ± 0.59°C (C). There were no significant differences (p < 0.05) in Tc, heart rate (HR), or &OV0312;o2 between intervals or treatments. We conclude that the RTX, in its current iteration, is ineffective at improving performance and/or mitigating thermal stress during high-intensity intermittent exercise.

Acceleration endurance with pressure breathing during G with and without a counterpressure vest.

INTRODUCTION The purpose of this study was to test whether pressure breathing during G (PBC) without a counterpressure vest negatively influences G endurance or increases breathing fatigue during extended duration high-G exposures. METHODS While using PBG, 10 subjects underwent 2 trials of +3 Gz exposures: once when wearing a counterpressure vest and once without. The exposures consisted of a relaxed, gradual G onset run until peripheral or central light loss, a straining rapid onset GC run to +6 Gz for 15 s, and a simulated aerial combat maneuver (SACM) G profile consisting of 10-s periods varying between +5 Gz and +9 Gz, during which subjects executed a hand-eye tracking task. The SACM endpoint was light loss or exhaustion. Subjects provided ratings of subjective effort and discomfort after the SACM. RESULTS Significant differences were found between the vest and no-vest conditions for only 3 of 19 measures: heart rate under G and two measures of tracking ability. The vast majority of data indicated no difference between the vest and no-vest conditions for performance under G. DISCUSSION This experiment supports previous studies and expands those previous results by increasing the duration of PBG exposure shown to not be influenced by wearing of the vest. We conclude that there is likely no practical advantage to wearing a counterpressure vest during PBG.