Counter-balanced Trials Research Articles

Does the Workload Change When Using an Impact Wrench in Different Postures?—A Counter-Balanced Trial

Awkward hand-arm posture and overhead work increase the risk of musculoskeletal symptoms. These adverse health effects can also be caused by additional workloads such as hand-arm vibration exposure while carrying or holding a power tool. This pilot trial investigated posture and muscle activity of 11 subjects while using an impact wrench for three working directions: upwards, forwards and downwards. Although the vibration exposure did not show notable differences in the magnitude (4.8 m/s2 upwards, 4.4 m/s2 forwards and 4.7 m/s2 downwards), postural behavior and the muscle activity showed significantly higher workloads for working upwards compared to forwards direction. The muscle activity results for working downwards also showed elevated levels of muscle activity due to the awkward wrist posture. The results demonstrate that not only the working direction but also more importantly the arm, wrist and head posture need to be considered while investigating hand-arm vibration exposure.

Sustained impact of energy-dense TV and online food advertising on children\u2019s dietary intake: a within-subject, randomised, crossover, counter-balanced trial

BackgroundPolicies restricting children’s exposure to unhealthy food marketing have been impeded by the lack of evidence showing a direct link between food advertising exposure and children’s energy intake and body weight. Food advertising exposure increases children’s immediate food consumption, but whether this increased intake is compensated for at later eating occasions is not known; consequently the sustained effect on diets remains unclear.MethodsWe conducted a within-subject, randomised, crossover, counterbalanced study across four, six-day holiday camps in New South Wales, Australia between April 2016 and January 2017. Children (7–12 years, n = 160) were recruited via local schools, email networks and social media. Two gender- and age-balanced groups were formed for each camp (n = 20), randomised to either a multiple- or single- media condition and exposed to food and non-food advertising in an online game and/or a television cartoon. Children’s food consumption (kilojoules) was measured at a snack immediately after exposure and then at lunch later in the day. Linear mixed models were conducted to examine relationships between food advertising exposure and dietary intake, taking into account gender, age and weight status.ResultsAll children in the multiple-media condition ate more at a snack after exposure to food advertising compared with non-food advertising; this was not compensated for at lunch, leading to additional daily food intake of 194 kJ (95% CI 80–308, p = 0.001, d = 0.2). Exposure to multiple-media food advertising compared with a single-media source increased the effect on snack intake by a difference of 182 kJ (95% CI 46–317, p = 0.009, d = 0.4). Food advertising had an increased effect among children with heavier weight status in both media groups.ConclusionOnline (‘advergame’) advertising combined with TV advertising exerted a stronger influence on children’s food consumption than TV advertising alone. The lack of compensation at lunch for children’s increased snack intake after food advertising exposure suggests that unhealthy food advertising exposure contributes to a positive energy-gap, which could cumulatively lead to the development of overweight.Trial registrationAustralian New Zealand Clinical Trials Registry, number ACTRN12617001230347 (Retrospectively registered).

Deep Ocean Mineral Supplementation Enhances the Cerebral Hemodynamic Response during Exercise and Decreases Inflammation Postexercise in Men at Two Age Levels.

Background: Previous studies have consistently shown that oral supplementation of deep ocean minerals (DOM) improves vascular function in animals and enhances muscle power output in exercising humans.Purpose: To examine the effects of DOM supplementation on the cerebral hemodynamic response during physical exertion in young and middle-aged men.Design: Double-blind placebo-controlled crossover studies were conducted in young (N = 12, aged 21.2 ± 0.4 years) and middle-aged men (N = 9, aged 46.8 ± 1.4 years). The counter-balanced trials of DOM and Placebo were separated by a 2-week washout period. DOM and Placebo were orally supplemented in drinks before, during, and after cycling exercise. DOM comprises desalinated minerals and trace elements from seawater collected ~618 m below the earth's surface.Methods: Cerebral hemodynamic response (tissue hemoglobin) was measured during cycling at 75% VO2max using near infrared spectroscopy (NIRS).Results: Cycling time to exhaustion at 75% VO2max and the associated plasma lactate response were similar between the Placebo and DOM trials for both age groups. In contrast, DOM significantly elevated cerebral hemoglobin levels in young men and, to a greater extent, in middle-aged men compared with Placebo. An increased neutrophil to lymphocyte ratio (NLR) was observed in middle-aged men, 2 h after exhaustive cycling, but was attenuated by DOM.Conclusion: Our data suggest that minerals and trace elements from deep oceans possess great promise in developing supplements to increase the cerebral hemodynamic response against a physical challenge and during post-exercise recovery for middle-aged men.

Localized and systemic variations in central motor drive at different local skin and muscle temperatures.

This study investigated the ability to sustain quadriceps central motor drive while subjected to localized heat and metaboreceptive feedback from the contralateral leg. Eight active males each completed two counter-balanced trials, in which muscle temperature (Tm) of a single-leg (TEMP-LEG) was altered to 29.4°C (COOL) or 37.6°C (WARM), while the contralateral leg (CL-LEG) remained thermoneutral: 35.3°C and 35.2°C Tm in COOL and WARM, respectively. To activate metaboreceptive feedback, participants first performed one 120-s isometric maximal voluntary contraction (MVC) of the knee extensors in the TEMP-LEG, immediately followed by postexercise muscle ischemia (PEMI) via femoral blood flow occlusion. To assess central motor drive of a remote muscle group immediately following PEMI, another 120-s MVC was subsequently performed in the CL-LEG. Voluntary muscle activation (VA) was assessed using the twitch interpolation method. Perceived mental effort and limb discomfort were also recorded. In a cooled muscle, a significant increase in mean force output and mean VA (force, P < 0.001; VA, P < 0.05), as well as a significant decrease in limb discomfort (P < 0.05) occurred during the sustained MVC in the TEMP-LEG. However, no differences between Tm were observed in mean force output, mean VA, or limb discomfort during the sustained MVC in the CL-LEG (force, P = 0.33; VA, P > 0.68; and limb discomfort, P = 0.73). The present findings suggest that elevated local skin temperature and Tm can increase limb discomfort and decrease central motor drive, but this does not limit systemic motor activation of a thermoneutral muscle group.

Effect of Standing or Walking at a Workstation on Cognitive Function: A Randomized Counterbalanced Trial.

In the present study, we examined the effect of working while seated, while standing, or while walking on measures of short-term memory, working memory, selective and sustained attention, and information-processing speed. The advent of computer-based technology has revolutionized the adult workplace, such that average adult full-time employees spend the majority of their working day seated. Prolonged sitting is associated with increasing obesity and chronic health conditions in children and adults. One possible intervention to reduce the negative health impacts of the modern office environment involves modifying the workplace to increase incidental activity and exercise during the workday. Although modifications, such as sit-stand desks, have been shown to improve physiological function, there is mixed information regarding the impact of such office modification on individual cognitive performance and thereby the efficiency of the work environment. In a fully counterbalanced randomized control trial, we assessed the cognitive performance of 45 undergraduate students for up to a 1-hr period in each condition. The results indicate that there is no significant change in the measures used to assess cognitive performance associated with working while seated, while standing, or while walking at low intensity. These results indicate that cognitive performance is not degraded with short-term use of alternate workstations.

Aspirin Ingestion Does Not Influence Local Sweat Responses during Exercise or Recovery in the Heat

Low-dose aspirin (ASA) therapy has been shown to alter skin blood flow responses and body temperature during heat stress in middle-aged participants. However, limited research has investigated the influence of aspirin on local sweat responses during continuous exercise and during passive recovery in the heat. PURPOSE: To investigate if, during exercise and/or recovery in the heat, acute ingestion of standard U.S. full-dose (325 mg) or low-dose (81 mg) ASA would alter indices of local sweat rate (SR). METHODS: Seven, healthy male participants (mean ± SD; 27 ± 5 years) completed counter-balanced trials to compare ASA treatments (325 mg ASA and 81 mg ASA) to a control trial (no ASA). A 10 day washout period was used to ensure normal blood platelet restoration between ASA treatments. Participants performed recumbent cycling in the heat (35 °C; 30-40% rH) for 45 min at an intensity initially corresponding to 50% heart rate reserve, followed by a 15 min passive recovery. A capacitance hygrometry capsule was placed on the dorsal aspect of participants forearm and used to continuously measure changes in local SR. RESULTS: ASA did not affect the onset of sweating with respect to core temperature (325 mg, 36.8 ± 0.3 °C; 81 mg, 36.8 ± 0.3 °C; control, 36.8 ± 0.4 °C; P = 0.82), SR sensitivity [(mg·cm−2·min−1)/°C] (325 mg, 0.69 ± 0.20; 81 mg, 0.67 ± 0.22; control, 0.69 ± 0.28; P = 0.94), or peak SR (mg·cm−2·min−1) (325 mg, 0.95 ± 0.24; 81 mg, 0.89 ± 0.18; control, 0.93 ± 0.26; P = 0.42) during exercise. Additionally, ASA did not appear to alter local SR among trials when expressed as percent change (%[INCREMENT]) from the cessation of exercise until the end of passive recovery (325 mg, −45 ± 21%; 81 mg, −53 ± 19%; control, −48 ± 26%; P = 0.70). CONCLUSION: Acute ASA ingestion did not affect thermoregulatory responses during submaximal exercise or passive recovery under the conditions of this investigation. Given the relatively youthful age and health status of present cohort, future research should seek to evaluate the influence of ASA on populations known to be at risk for heat-related illness (e.g., type 2 diabetes, spinal cord injury).

Acetylsalicylic acid does not alter thermo-effector responses during mild whole-body passive heat stress in young men

Acetylsalicylic acid (ASA), aspirin, exerts potent systemic effects that may interfere with normal thermo-effector responses. We investigated the influence of commonly ingested ASA doses on measures of skin blood flow (SkBF) and local sweat rate (SR) during whole-body, passive heat stress. Seven male participants completed counter-balanced trials to compare ASA treatments (single dose 325 mg or 4 consecutive days 81 mg (4-d 81 mg)) to control (no ASA). Laser-Doppler flowmetry provided an index of SkBF. A ventilated capsule measured local sweat rate via capacitance hygrometry. Mean body temperature () was increased by 1 °C above baseline using a water-perfused suit. was similar at the onset of cutaneous vasodilation among trials. Cutaneous vascular conductance, expressed as a percentage change from baseline, was not different among trials. Additionally, at the onset of local SR and SR sensitivity did not differ among trials. While ASA has previously been shown to influence SkBF during heat stress, it is possible our cohort’s relatively young age may have contributed to our dissimilar results.

Hand-Rim Forces and Gross Mechanical Efficiency in Asynchronous and Synchronous Wheelchair Propulsion: A Comparison

To compare the force application characteristics at various push frequencies of asynchronous (ASY) and synchronous (SYN) hand-rim propulsion, 8 able-bodied participants performed a separate sub-maximal exercise test on a wheelchair roller ergometer for each propulsion mode. Each test consisted of a series of 5, 4-min exercise blocks at 1.8 m · s-1 - initially at their freely chosen frequency (FCF), followed by four counter-balanced trials at 60, 80, 120 and 140% FCF. Kinetic data was obtained using a SMARTWheel, measuring forces and moments. The gross efficiency (GE) was determined as the ratio of external work done and the total energy expended. The ASY propulsion produced higher force measures for FRES, FTAN, rate of force development & FEF (P<0.05), while there was no difference in GE values (P=0.518). In pair-matched push frequencies (ASY80:SYN60, ASY100:SYN80, ASY120:SYN100 and ASY140:SYN120), ASY propulsion forces remained significantly higher (FRES, FTAN, rate of force development & FEF P<0.05), and there was no significant effect on GE (P=0.456). Both ASY and SYN propulsion demonstrate similar trends: changes in push frequency are accompanied by changes in absolute force even without changes in the gross pattern/trend of force application, FEF or GE. Matched push frequencies continue to produce significant differences in force measures but not GE. This suggests ASY propulsion is the predominant factor in force application differences. The ASY would appear to offer a kinetic disadvantage to SYN propulsion and no physiological advantage under current testing conditions.

Effect of Tolcapone on Brain Activity During a Variable Attentional Control Task: A Double-Blind, Placebo-Controlled, Counter-Balanced Trial in Healthy Volunteers

Attention is the capacity to flexibly orient behaviors and thoughts towards a goal by selecting and integrating relevant contextual information. The dorsal cingulate (dCC) and prefrontal (PFC) cortices play critical roles in attention. Evidence indicates that catechol-O-methyltransferase (COMT) modulates dopaminergic tone in the PFC and dCC. In this study, we explored the effect of tolcapone, a CNS penetrant COMT inhibitor that increases cortical dopamine levels, on brain activity during a Variable Attentional Control (VAC) task. We performed a double-blinded, placebo-controlled, counter-balanced trial with tolcapone (Tasmar, tablets, 100 mg three times a day for 1 day and then 200 mg three times a day for 6 days; ClinicalTrials.gov identifier: NCT00044083). The study was conducted in the Clinical Center of the National Institute of Mental Health from 2005 to 2009. Twenty healthy volunteers (11 males; mean age = 32.7 years) with good imaging and performance data on both arms of the study were investigated. Participants underwent 3T blood-oxygen-level-dependent (BOLD) functional magnetic resonance imaging (fMRI) while performing the event-related VAC task, which varies attention over three levels of load: LOW, INT (intermediate), and HIGH. Changes in behavioral data and individual contrast images were analyzed using ANOVA with drug and task load as co-factors. There was a significant main effect of increasing task load, with resulting decreased accuracy and increased reaction time. While there was no significant effect of tolcapone on these behavioral measures, the neuroimaging data showed a significant effect on load-related changes in dCC, with significantly lower dCC activation on tolcapone compared with placebo. Further, neural activity in dCC correlated positively with COMT enzyme activity (i.e., lower COMT activity and presumably more dopamine was associated with lower activation in dCC, i.e., more efficient information processing). Our results show that pharmacological reduction of COMT activity modulates the engagement of attentional mechanisms, selectively enhancing the efficiency of dCC processing in healthy volunteers, reflected as decreased activity for the same level of performance.

Hand-rim Forces and Gross Mechanical Efficiency at Various Frequencies of Wheelchair Propulsion

To determine the effects of push frequency changes on force application, fraction of effective force (FEF) and gross efficiency (GE) during hand-rim propulsion. 8 male able-bodied participants performed five 4-min sub-maximal exercise bouts at 1.8 ms(-1); the freely chosen frequency (FCF), followed by 4 counter-balanced trials at 60, 80, 120 and 140% FCF. Kinetic data was obtained using a SMART(Wheel), measuring forces and moments. The GE was determined as the ratio of external work done and the total energy expended. Increased push frequency led to reductions in peak resultant force (P<0.05), ranging from 167 to 117 N and peak tangential force (P<0.05), ranging from 117 to 77 N. However, FEF only demonstrated a significant difference between 60% and 140% FCF (69 ± 9% and 63 ± 7, respectively; P<0.05). Work per cycle decreased significantly (P<0.05) and rate of force development increased significantly (P<0.05) with increased push frequency. GE values were significantly lower at 60%, 120% and 140% FCF than 80% and 100% FCF (P<0.05). No meaningful associations were present between FEF and GE. Under the current testing conditions, changes in push frequency are accompanied with changes in the absolute force values, albeit without changes in either the gross pattern/trend of force application or FEF. Changes in GE are not explained by different levels of force effectiveness.

Presence of Observers Increases One Repetition Maximum in College-age Males and Females

Purpose: To determine if the presence of observers affects muscular strength performance in college-age males and females. Methods: Twenty-five women and 24 men participated in the study. Two counter-balanced trials were performed in which participants completed 1-RM tests in bench press and leg press. During one trial, two members of the opposite gender observed the 1-RM tests. During the other trial there were no observers, other than the tester. Results: 1-RM for females increased 3.4±0.8 lbs on bench press (p&lt;.001) and increased 9.2±3.8 lbs on leg press (p=.025) when observers were present. 1-RM for males increased 4.2±1.1 lbs on bench press (p=.001) and increased 18.8±5.2 lbs on leg press (p=.002) with observers present. There was no difference in the percent increase in 1-RM between males and females for either leg press (p=.71) or bench press (p=.08). Conclusion: College-age males and females lifted more weight during a 1-RM test when observers were present.

Effects of Arm Frequency during Synchronous and Asynchronous Wheelchair Propulsion on Efficiency

To further understand the possible underlying mechanisms of the low efficiencies in hand rim wheelchair propulsion, this study examined efficiency indices at different arm frequencies during two propulsion modes (synchronous and asynchronous). Fourteen male able-bodied participants performed VO2PEAK tests for both propulsion modes. Subsequently two sub-maximal exercise tests examining synchronous and asynchronous propulsion were completed at an individualised velocity (60% of VO2PEAK). The freely chosen arm frequency (FCF), followed by four counter-balanced trials at 60, 80, 120, and 140% of FCF were performed. Gross, net, and work efficiency were determined. Gross efficiency was significantly lower (p<0.05) at arm frequencies >100%, and participants were more efficient between 60 to 100% FCF. These arm frequencies corresponded to 76+/-22 to 126+/-36 and 70+/-18 to 116+/-30 pushes x min(-1) (synchronous and asynchronous respectively). Trends in VO2, gross and work efficiency suggest that 80% of FCF produced the best economy and efficiency during both propulsion modes (non-significant). Gross and work efficiency at 80% FCF were 6.8+/-0.7% and 13.0+/-4.6% for synchronous and 7.0+/-0.8% and 11.5+/-1.6% for asynchronous respectively. The results suggest that during both modes of propulsion the FCF is not necessarily the most efficient.

The Role of Dehydration and Electrolyte Loss on Exercise-Associated Muscle Cramps

1241 Dehydration, electrolyte imbalance, environmental stress, and neuromuscular fatigue have all been implicated as potential causes of exercise-associated muscle cramps (EAMC). Additionally, maintenance of fluid and electrolyte balance is often prescribed in the prevention of EAMC. However, there is little scientific data to support these assertions. PURPOSE: To determine the role of hydration and electrolyte balance in the prevention of EAMC. METHODS: Thirteen, college-aged males each completed two counter-balanced trials in a repeated-measures design. In each trial, participants performed a calf-fatiguing protocol known to induce EAMC in the calf muscle group. Each trial was performed in the same hot environment (dry bulb = 37 C, relative humidity = 60%). Participants consumed a carbohydrate-electrolyte beverage two hours and 30 minutes prior to each trial in order to optimize hydration and electrolyte levels. In one trial (euhydrated), participants consumed a carbohydrate-electrolyte beverage (with 3.0g NaCl added per liter of fluid) at a rate similar to sweat loss. In a second trial (hypohydrated), subjects were not allowed to consume any fluids. RESULTS: Cramps were induced in nine of the participants, while seven participants cramped in both trials. For those who cramped in both trials exercise duration prior to the onset of EAMC was significantly longer in the euhydrated trial (36.8 ± 17.3 minutes) compared to the hypohydrated trial (14.6 ± 5.0 minutes; p < .01). Mean weight loss for the hypohydrated trial was 1.0% ± 0.4% of body mass. No weight loss occurred during the euhydrated trial. CONCLUSIONS: The results suggest that dehydration and electrolyte loss are not the singular cause(s) of EAMC, since subjects cramped when they were euhydrated and in electrolyte balance. However, it appears that consumption of a carbohydrate-electrolyte beverage prior to and during exercise in a hot environment may delay the onset of EAMC.