Robin Callister

Age and gender influence muscle sympathetic nerve activity at rest in healthy humans.

Muscle sympathetic nerve activity at rest increases with age in humans. The respective influences of the aging process per se and gender on this increase and whether age and gender effects on muscle sympathetic nerve activity can be identified with plasma norepinephrine concentrations, however, have not been established. To examine these issues, nine young women (aged 24 +/- 1 years; mean +/- SEM), eight young men (aged 26 +/- 1 years), seven older women (aged 63 +/- 1 years), and eight older men (aged 66 +/- 1 years) were studied. All were healthy, normotensive (blood pressure < 140/90 mm Hg), nonobese (< 20% above ideal weight), unmedicated, nonsmokers engaged in minimal to recreational levels of chronic physical activity. Arterial blood pressure (manual sphygmomanometry, brachial artery), heart rate, muscle sympathetic nerve activity (peroneal microneurography), and antecubital venous plasma norepinephrine concentrations (radioenzymatic assay) were determined during quiet supine resting conditions. Body weight was higher in men, but there were no age-related differences, whereas estimated body fat (sum of skinfolds) was higher in women and in the older groups (p < 0.05). Estimated daily energy expenditure, arterial blood pressure, and heart rate were not different among the groups. Both muscle sympathetic nerve activity burst frequency and burst incidence at rest were progressively higher in the young women, young men, older women, and older men (10 +/- 1 versus 18 +/- 2 versus 25 +/- 3 versus 39 +/- 5 bursts/min and 16 +/- 1 versus 30 +/- 4 versus 40 +/- 3 versus 61 +/- 6 bursts/100 heartbeats, respectively; all p < 0.05 versus each other).(ABSTRACT TRUNCATED AT 250 WORDS)

Sympathetic activity is influenced by task difficulty and stress perception during mental challenge in humans.

1. Our aim was to determine the influence of the type of task, the absolute and relative difficulty of the task, and the perceived stress associated with performance of the task on sympathetic circulatory regulation during cognitive challenge in humans. 2. Sympathetic nerve activity to skeletal muscle (MSNA) determined from peroneal microneurography, heart rate and arterial blood pressure were recorded continuously in twelve subjects during a modified Stroop colour word test (CWT) and mental arithmetic (MA), each performed over six levels of increasing absolute task difficulty. Performance (percentage correct) on each task was assessed and ratings of perceived stress obtained. Responses to CWT and MA were compared at similar levels of performance and perceived stress. 3. MSNA decreased at task onset, remained below baseline levels at low levels of difficulty which were not perceived as stressful, increased above baseline levels at higher levels of difficulty which were perceived as stressful, and increased further during recovery. Thus, the regulation of MSNA was stress dependent. At similar levels of stress perception there were no differences in MSNA between CWT and MA. Although performance declined as task difficulty increased, there was no particular ‘threshold’ level of performance associated with the stimulation of MSNA. 4. Arterial pressure and heart rate were elevated above baseline levels throughout the mental tasks. Arterial pressure increased over the first 3‐4 levels of each task and then plateaued whereas heart rate did not vary across increasing levels of task difficulty. Heart rate and arterial pressure responses to CWT were higher than those to MA. 5. These data demonstrate that during cognitive challenge the stimulation of MSNA is governed primarily by perceived stress which is dependent, in part, on the absolute level of task difficulty. In contrast, neither performance nor the type of cognitive task appear to be important determinants of MSNA. Arterial pressure is influenced by the task and level of difficulty. Heart rate is independent of task difficulty but may be task dependent.

Is your prescription of distance running shoes evidence-based?

Objectives: To determine whether the current practice of prescribing distance running shoes featuring elevated cushioned heels and pronation control systems tailored to the individual’s foot type is evidence-based. Data sources: MEDLINE (1950–May 2007), CINAHL (1982–May 2007), EMBASE (1980–May 2007), PsychInfo (1806–May 2007), Cochrane Database of Systematic Reviews (2nd Quarter 2007), Cochrane Central Register of Controlled trials (2nd Quarter 2007), SPORTSDiscus (1985–May 2007) and AMED (1985–May 2007). Review methods: English language articles were identified via keyword and medical subject headings (MeSH) searches of the above electronic databases. With these searches and the subsequent review process, controlled trials or systematic reviews were sought in which the study population included adult recreational or competitive distance runners, the exposure was distance running, the intervention evaluated was a running shoe with an elevated cushioned heel and pronation control systems individualised to the wearer’s foot type, and the outcome measures included either running injury rates, distance running performance, osteoarthritis risk, physical activity levels, or overall health and wellbeing. The quality of these studies and their findings were then evaluated. Results: No original research that met the study criteria was identified either directly or via the findings of the six systematic reviews identified. Conclusion: The prescription of this shoe type to distance runners is not evidence-based.

12-month outcomes and process evaluation of the SHED-IT RCT: an Internet-based weight loss program targeting men

This article reports the 12‐month follow‐up results and process evaluation of the SHED‐IT (Self‐Help, Exercise, and Diet using Information Technology) trial, an Internet‐based weight loss program exclusively for men. Sixty‐five overweight/obese male staff and students at the University of Newcastle (Callaghan, Australia) (mean (s.d.) age = 35.9 (11.1) years; BMI = 30.6 (2.8)) were randomly assigned to either (i) Internet group (n = 34) or (ii) Information only control group (n = 31). Both received one face‐to‐face information session and a program booklet. Internet group participants were instructed to use the study website for 3 months. Participants were assessed at baseline, 3‐, 6‐, and 12‐month follow‐up for weight, waist circumference, BMI, blood pressure, and resting heart rate. Retention at 3‐ and 12‐months was 85% and 71%, respectively. Intention‐to‐treat (ITT) analysis using linear mixed models revealed significant and sustained weight loss of −5.3 kg (95% confidence interval (CI): −7.5, −3.0) at 12 months for the Internet group and −3.1 kg (95% CI: −5.4, −0.7) for the control group with no group difference. A significant time effect was found for all outcomes (P < 0.001). Per‐protocol analysis revealed a significant group‐by‐time interaction for weight, waist circumference, BMI, and systolic blood pressure. Internet group compliers (who self‐monitored as instructed) maintained greater weight loss at 12 months (−8.8 kg; 95% CI −11.8, −5.9) than noncompliers (−1.9 kg; 95% CI −4.8, 1.0) and controls (−3.0 kg; 95% CI −5.2, −0.9). Qualitative analysis by questionnaire and interview highlighted the acceptability and satisfaction with SHED‐IT. Low‐dose approaches to weight loss are feasible, acceptable, and can achieve clinically important weight loss in men after 1‐year follow‐up.

Efficacy of a workplace-based weight loss program for overweight male shift workers: the Workplace POWER (Preventing Obesity Without Eating like a Rabbit) randomized controlled trial

OBJECTIVE To evaluate the feasibility and efficacy of a workplace-based weight loss program (Workplace POWER-WP) for male shift workers. METHOD A prospective, two-armed randomized controlled trial of 110 overweight/obese (BMI 25-40) (mean [SD] age = 44.4 [8.6] years; BMI = 30.5 [3.6]) male employees at Tomago Aluminium aged 18-65. In October (2009) men were randomized to either (i) WP program (n=65) or (ii) a 14-week wait-list control group (n=45). The 3-month program involved one information session, program booklets, group-based financial incentives and an online component. Men were assessed at baseline and at 14-week follow-up for weight (primary outcome), waist circumference, BMI, blood pressure, resting heart rate, self-reported physical activity and dietary variables, and physical activity and dietary cognitions. RESULTS Intention-to-treat analysis using linear mixed models revealed significant between group differences for weight loss after 14 weeks (P < .001, Cohens d = 0.34). Significant intervention effects were also found for waist circumference (P < .001, d = 0.63), BMI (P < .001, d = 0.41), systolic blood pressure (P = .02, d = 0.48), resting heart rate (P < .001, d = 0.81), physical activity (P = .03, d = 0.77), sweetened beverages (P < .02, d = 0.5-0.6) and physical activity-related cognitions (P < .02, d=0.6). CONCLUSION The WP program was feasible and efficacious and resulted in significant weight loss and improved health-related outcomes and behaviours in overweight male shift workers.

Dietary restriction and exercise improve airway inflammation and clinical outcomes in overweight and obese asthma: a randomized trial

Obesity and asthma are associated conditions; however, the mechanisms linking the two remain unclear. Few studies have examined the effects of weight loss on inflammation and clinical outcomes in obese–asthma.

The 'Healthy Dads, Healthy Kids' randomized controlled trial: efficacy of a healthy lifestyle program for overweight fathers and their children.

Objective:To evaluate the feasibility and efficacy of the ‘Healthy Dads, Healthy Kids’ (HDHK) program, which was designed to help overweight fathers lose weight and be a role model of positive health behaviors for their children.Design:Randomized controlled trial.Participants:A total of 53 overweight/obese men (mean (s.d.) age=40.6 (7.1) years; body mass index (BMI)=33.2 (3.9)) and their primary school-aged children (n=71, 54% boys; mean (s.d.) age=8.2 (2.0) years) were randomly assigned (family unit) to either (i) the HDHK program (n=27 fathers, n=39 children) or (ii) a wait-list control group (n=26 fathers, n=32 children).Intervention:Fathers in the 3-month program attended eight face-to-face education sessions. Children attended three of these sessions.Outcomes:The primary outcome was fathers’ weight. Fathers and their children were assessed at baseline, and at 3- and 6-month follow-up, for weight, waist circumference, BMI, blood pressure, resting heart rate (RHR), objectively measured physical activity and self-reported dietary intake.Results:Intention-to-treat analysis revealed significant between-group differences at 6 months for weight loss (P<0.001), with HDHK fathers losing more weight (−7.6 kg; 95% confidence interval (CI) −9.2, −6.0; d=0.54) than control group fathers (0.0 kg; 95% CI −1.4, 1.6). Significant treatment effects (P<0.05) were also found for waist circumference (d=0.62), BMI (d=0.53), systolic blood pressure (d=0.92), RHR (d=0.66) and physical activity (d=0.91), but not for dietary intake. In children, significant treatment effects (P<0.05) were found for physical activity (d=0.74), RHR (d=0.51) and dietary intake (d=0.84).Conclusion:The HDHK program resulted in significant weight loss and improved health-related outcomes in fathers and improved eating and physical activity among children. Targeting fathers is a novel and efficacious approach to improving health behavior in their children.

Preventing Obesity Among Adolescent Girls: One-Year Outcomes of the Nutrition and Enjoyable Activity for Teen Girls (NEAT Girls) Cluster Randomized Controlled Trial

OBJECTIVE To evaluate the impact of a 12-month multicomponent school-based obesity prevention program, Nutrition and Enjoyable Activity for Teen Girls among adolescent girls. DESIGN Group randomized controlled trial with 12-month follow-up. SETTING Twelve secondary schools in low-income communities in the Hunter and Central Coast regions of New South Wales, Australia. PARTICIPANTS Three hundred fifty-seven adolescent girls aged 12 to 14 years. INTERVENTION A multicomponent school-based intervention program tailored for adolescent girls. The intervention was based on social cognitive theory and included teacher professional development, enhanced school sport sessions, interactive seminars, nutrition workshops, lunch-time physical activity sessions, handbooks and pedometers for self-monitoring, parent newsletters, and text messaging for social support. MAIN OUTCOME MEASURES Body mass index (BMI, calculated as weight in kilograms divided by height in meters squared), BMI z score, body fat percentage, physical activity, screen time, dietary intake, and self-esteem. RESULTS After 12 months, changes in BMI (adjusted mean difference, -0.19; 95% CI, -0.70 to 0.33), BMI z score (mean, -0.08; 95% CI, -0.20 to 0.04), and body fat percentage (mean, -1.09; 95% CI, -2.88 to 0.70) were in favor of the intervention, but they were not statistically different from those in the control group. Changes in screen time were statistically significant (mean, -30.67 min/d; 95% CI, -62.43 to -1.06), but there were no group by time effects for physical activity, dietary behavior, or self-esteem. CONCLUSIONS A school-based intervention tailored for adolescent girls from schools located in low-income communities did not significantly reduce BMI gain. However, changes in body composition were of a magnitude similar to previous studies and may be associated with clinically important health outcomes. TRIAL REGISTRATION anzctr.org.au Identifier: 12610000330044.

Sympathetic nervous system activity during skin cooling in humans: relationship to stimulus intensity and pain sensation.

1. Our aim was to determine the relationship between efferent sympathetic nervous system activity to skeletal muscle (MSNA) and both the dynamics of the stimulus and pain sensation during localized skin cooling in humans. MSNA in the lower leg (peroneal microneurography), heart rate, arterial blood pressure, hand skin and muscle temperatures and perceptions of pain were recorded in ten healthy subjects before, during and after immersion (3 min) of a hand in water of different temperatures ranging from non‐noxious to extremely noxious (28, 21, 14, 7 and 0 degrees C). 2. Immersion produced an abrupt, water temperature‐dependent fall in hand skin temperature (initial 30 s) followed by a more gradual decline. In contrast, the fall in hand muscle temperature was almost linear during immersion. Throughout immersions at the 28, 21, and 14 degrees C water temperatures and during the initial phase of the 7 degrees C level, sensations ranged from not painful to somewhat painful; however, the latter phase of the 7 degrees C immersion and the entire 0 degrees C level were perceived as intensely painful. 3. During the initial 15‐30 s of immersion at the 21‐7 degrees C water temperatures, MSNA decreased from control levels in all subjects (47‐58% on average, P < 0.05), whereas mean arterial blood pressure did not change. MSNA then returned to and remained at control levels throughout the 28‐14 degrees C immersions, although arterial pressure, primarily systolic, rose slightly. 4. After some delay, MSNA increased during immersion at both the 7 degrees C (P < 0.05 at 90 s) and 0 degrees C (P < 0.05 at 60 s) levels in a progressive, water temperature‐dependent manner, achieving peak values of approximately 200 and 300% of control, respectively, by 2.0‐2.5 min. These elevations in MSNA were associated with parallel increases in arterial pressure. 5. Heart rate rose during the onset of immersion at all water temperatures (P < 0.05), but fell rapidly to control levels after 60‐90 s. The increases were small (approximately 5 beats/min) and similar at the 28‐7 degrees C levels, but were twice as great at the coldest water temperature.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of integrating pedometers, parental materials, and E-mail support within an extracurricular school sport intervention.

PURPOSE The objective of this study was to evaluate the impact of a school-based intervention (Program X) incorporating pedometers and e-mail support on physical activity, sedentary behavior, and healthy eating in adolescents. METHODS A randomized control trial was used to evaluate the impact of the Program X intervention. Six schools (N = 124 participants; mean age 14.1 +/- .8 years) were randomized to intervention or control conditions for the 6-month study period. Objectively recorded physical activity (mean steps/day), self-reported sedentary behavior, and dietary habits were measured at baseline and at 6-month follow-up and intervention effects were assessed using repeated-measures analysis of variance and chi(2) tests. RESULTS Participants in the intervention group increased their step counts by 956 +/- 4107 steps/day (boys) and 999 +/- 1999 (girls). Repeated-measures analysis of variance revealed significant group-by-time interactions for boys (F = 7.4, p = .01, d = .80) and girls (F = 29.6, p <.001, d = 1.27) for mean steps/day. The intervention significantly decreased the number of energy-dense/low-nutrient snacks consumed by boys (chi(2) = 4.0, p = .043) and increased the number of fruit serves among girls (chi(2) = 4.8, p = .028). The intervention did not have a statistically significant effect on sedentary behavior. CONCLUSION A school-based intervention incorporating physical activity monitoring using pedometers and e-mail support was successful in promoting physical activity and selected healthy eating behaviors in adolescent boys and girls.