Passive limb movement intervals results in repeated hyperemic responses in those with paraplegia.

STUDY DESIGN: Repeated measures. OBJECTIVES: Reports suggest passive limb movement (PLM) could be used as a therapy to increase blood flow and tissue perfusion in the paralyzed lower limbs of those with spinal cord injuries. However, the hyperemic response to PLM appears to be transient, lasting only 30-45 s despite continued limb movement. The purpose of this investigation was to determine whether the hyperemic response is repeatable across multiple short bouts of passive limb movement. SETTING: Cleveland Veterans Affairs Medical Center. METHODS: Nine individuals with paraplegia 46 ± 6 years of age, 17 ± 12 years post injury (range: 3-33 years) with complete T3-T11 injuries were subject to 5 × 1 min bouts of passive knee extension/flexion at 1 Hz with a 1 min recovery period between each bout. Heart rate (HR), mean arterial pressure (MAP), femoral artery blood flow (FABF), skin blood flow (SBF), and tissue perfusion in the lower limb were recorded during baseline and throughout each bout of PLM. RESULTS: Despite no increase in HR (p ≥ 0.8) or MAP (p ≥ 0.40) across all four bouts of PLM, the average increase in FABF during each bout ranged from 71 ± 87% to 88 ± 93% greater than baseline (p ≤ 0.043). SBF also increased between 465 ± 302% and 582 ± 309% across the five bouts of PLM (p ≤ 0.005). CONCLUSIONS: Repeated bouts of PLM in those with SCI while in an upright position resulted in a robust and steady increase in FABF and SBF which could have implications for improving vascular health and tissue perfusion in the lower limbs of those with paraplegia.

Pilot physiology, cognition and flight performance during flight simulation exposed to a 3810-m hypoxic condition.

BACKGROUND: Hypoxia is a physiological state defined as a reduction in the distribution of oxygen to the tissues of the body. It has been considered a major factor in aviation safety worldwide because of its potential for pilot disorientation. Pilots are able to operate aircrafts up to 3810 m without the use of supplemental oxygen and may exhibit symptoms associated with hypoxia. OBJECTIVE: To determine the effects of 3810 m on physiology, cognition and performance in pilots during a flight simulation. METHODS: Ten healthy male pilots engaged in a counterbalanced experimental protocol comparing a 0-m normoxic condition (NORM) with a 3810-m hypoxic condition (HYP) on pilot physiology, cognition and flight performance. RESULTS: Repeated-measures analysis of variance demonstrated a significant (p ≤ 0.05) time by condition interaction for physiological and cognitive alterations during HYP. A paired-samples t test demonstrated no differences in pilot performance (p ≥ 0.05) between conditions. CONCLUSION: Pilots exhibited physiological and cognitive impairments; however, pilot performance was not affected by HYP.

The cardiovascular response to passive movement is joint dependent.

The cardiovascular responses to passive limb movement (PLM) at the knee are well established, however, responses to PLM at other joints involving smaller muscle volume are unknown. To compare the cardiovascular responses to passive movement at other joints, 10 participants underwent a PLM protocol in which the wrist, elbow, ankle, and knee joints were passively extended and flexed at 1 Hz for 1 min. Heart rate (HR), mean arterial blood pressure (MAP), and arterial blood flow to that limb segment (BF) were measured and vascular conductance (VC) was calculated for a 30-sec baseline period and for 3-sec intervals throughout PLM protocols. PLM of the knee and elbow resulted in significant increases in BF and VC from baseline values with peak values 180% (P < 0.001) greater than baseline. PLM of the elbow resulted in significant increases in BF and VC from baseline values with peak values 109% and 115% (P < 0.001) greater than baseline, respectively. No changes in BF and VC were observed in the ankle and wrist. Furthermore, the greater increase in blood flow per limb segment volume in the thigh and upper arm (62.8 ± 36.5 and 55.5 ± 30.3 mL min(-1) L(-1), respectively) compared to the forearm and lower leg (23.6 ± 16.7 and 19.1 ± 10.3 mL min(-1) L(-1), respectively) indicates the limb volume is not solely responsible for the differences in the hyperemic responses. These data indicate that the use of PLM to assess vascular function or as a rehabilitation modality to maintain vascular health may be most appropriate for the muscles that span the elbow and knee.

Response to Letter to the Editor: a counterweight is not necessary to implement simple, natural and comfortable single-leg cycle training.

Dr. Dolmage and colleagues commented on a recent publication titled, "Cardiovascular responses to counterweighted single-leg cycling: implications for rehabilitation." They assert that a counterweight is not required to facilitate natural single-leg cycling, rather a fixed gear ergometer can also accomplish the same goal. We agree with Dolmage and colleagues that a fixed gear ergometer can facilitate natural single-leg cycling with minimal deviation in the angular velocity of the crank if the kinetic energy of the flywheel is large. We also present some simple comparisons between the two modalities.

Do glucose containing beverages play a role in thermoregulation, thermal sensation, and mood state?

INTRODUCTION: Dehydration limits the appropriate delivery of oxygen and substrates to the working muscle. Further, the brain's ability to function may also be compromised whereby thermal sensation and mood state may be altered. PURPOSE: The purpose of the present investigation was to compare the thermoregulatory, perceptual, and negative mood state profile in glucose (GLU) vs. non-glucose beverage (NON-GLU) condition. METHODS: Ten healthy men volunteered and were counterbalanced either a GLU or NON-GLU containing beverage on separate mornings. In each condition, they were exposed to 37°C, 50% relative humidity (RH) for baseline, exercise, rehydration, and recovery periods. The exercise period elicited the desired level of dehydration (mean of 2.6 ± 0.3% body weight losses). Upon completion of the protracted exercise, participants were administered either a GLU or NON-GLU containing electrolyte based sports drink ad libitum for 30 min, followed by a recovery period of 15 min in 37°C, 50% RH. Rectal (Tre) and mean skin temperatures (Tsk) were continuously monitored. Gagge (TS) and heated thermal sensation (HTS), profile of mood state (POMS) were measure at the end of each period. RESULTS: During recovery after rehydration, Tre was not significantly different between conditions (GLU vs. NON-GLU) (37.4 ± 0.8 vs. 37.0 ± 1.2°C); Tsk was also not affected by rehydration in both conditions (36.0 ± 0.5 vs. 36.0 ± 0.6°C) and, TS and HTS did not differ between conditions (0.9 ± 1.3 vs.1.3 ± 0.7) and (1.0 ± 0.8 vs.0.8 ± 0.3). Total mood disturbance (TMD) score for the POMS was utilized for overall negative mood state and demonstrated a main effect for time (p < 0.05). TMD during recovery was decreased compared to before hydration in both conditions. CONCLUSION: The non-glucose containing beverage maintained plasma volume and was effective at maintaining body temperature homeostasis in a similar fashion compared to the glucose containing beverage. Furthermore, negative mood state was not different between the two conditions. The non-glucose beverages can serve a valuable role in the exercise environment depending upon the sport, the ambient temperature, the individual, duration of the exercise, the age and training states of the individual.

Cardiovascular responses to counterweighted single-leg cycling: implications for rehabilitation.

PURPOSE: Although difficult to coordinate, single-leg cycling allows for greater muscle-specific exercise capacity and subsequently greater stimulus for metabolic and vascular adaptations compared to typical double-leg cycling. The purpose of this investigation was to compare metabolic, cardiovascular and perceptual responses of double-leg cycling to single-leg cycling with and without the use of a counterweight. METHODS: Ten healthy individuals (age 22 ± 2 years; body mass 78.0 ± 11.2 kg; height 1.8 ± 0.1 m) performed three cycling conditions consisting of double-leg cycling (DL), non-counterweighted single-leg cycling (SLNCW) and single-leg cycling with a 97 N counterweight attached to the unoccupied crank arm (SLCW). For each condition, participants performed cycling trials (80 rpm) at three different work rates (40, 80 and 120 W). Oxygen consumption (VO2), respiratory exchange ratio (RER), heart rate (HR), femoral blood flow, rating of perceived exertion (RPE) and liking score were measured. RESULTS: VO2 and HR were similar for DL and SLCW conditions. However, during SLNCW, VO2 was at least 23 ± 13 % greater and HR was at least 15 ± 11 % greater compared to SLCW across all three intensities. Femoral blood flow was at least 65.5 ± 43.8 % greater during SLCW compared to DL cycling across all three intensities. RPE was lower and liking scores were greater for SLCW compared to SLNCW condition. CONCLUSION: Counterweighted single-leg cycling provides an exercise modality that is more tolerable than typical single-leg cycling while inducing greater peripheral stress for the same cardiovascular demand as double-leg cycling.

Cold habituation does not improve manual dexterity during rest and exercise in 5 °C.

When exposed to a cold environment, a barehanded person experiences pain, cold sensation, and reduced manual dexterity. Both acute (e.g. exercise) and chronic (e.g. cold acclimatization or habituation) processes might lessen these negative effects. The purpose of this experiment was to determine the effect of cold habituation on physiology, perception, and manual dexterity during rest, exercise, and recovery in 5 °C. Six cold weather athletes (CWA) and eight non habituated men (NON) volunteered to participate in a repeated measures cross-over design. The protocol was conducted in 5 °C and was 90 min of resting cold exposure, 30 min of cycle ergometry exercise (50 % VO2 peak), and 60 min of seated recovery. Core and finger skin temperature, metabolic rate, Purdue Pegboard dexterity performance, hand pain, thermal sensation, and mood were quantified. Exercise-induced finger rewarming (EIFRW) was calculated for each hand. During 90 min of resting exposure to 5 °C, the CWA had a smaller reduction in finger temperature, a lower metabolic rate, less hand pain, and less negative mood. Despite this cold habituation, dexterity performance was not different between groups. In response to cycle ergometry, EIFRW was greater in CWA (~12 versus 7 °C) and occurred at lower core temperatures (37.02 versus 37.31 °C) relative to NON but dexterity was not greater during post-exercise recovery. The current data indicate that cold habituated men (i.e., CWA) do not perform better on the Purdue Pegboard during acute cold exposure. Furthermore, despite augmented EIFRW in CWA, dexterity during post-exercise recovery was similar between groups.