Respiratory Responses during Exercise in Self-contained Breathing Apparatus among Firefighters and Nonfirefighters.

BACKGROUND: Firefighters are required to use self-contained breathing apparatus (SCBA), which impairs ventilatory mechanics. We hypothesized that firefighters have elevated arterial CO2 when using SCBA. METHODS: Firefighters and controls performed a maximal exercise test on a cycle ergometer and two graded exercise tests (GXTs) at 25%, 50%, and 70% of their maximal aerobic power, once with a SCBA facemask and once with protective clothing and full SCBA. RESULTS: Respiratory rate increased more in controls than firefighters. Heart rate increased as a function of oxygen consumption ( V . O 2 ) more in controls than firefighters. End-tidal CO2 (ETCO2) during the GXTs was not affected by work rate in either group for either condition but was higher in firefighters at all work rates in both GXTs. SCBA increased ETCO2 in controls but not firefighters. CONCLUSIONS: The present study showed that when compared to controls, firefighters' hypoventilate during a maximal test and GXT. The hypoventilation resulted in increased ETCO2, and presumably increased arterial CO2, during exertion. It is proposed that firefighters have altered CO2 sensitivity due to voluntary hypoventilation during training and work. Confirmation of low CO2 sensitivity and the consequence of this on performance and long-term health remain to be determined.

Effect of rehydration schedule after four-hour head-out water immersion on running performance and recovery.

Introduction: Head-out water immersion (HOWI) results in diuresis, which could potentially limit performance after egress to land. We examined the effect of rehydration on endurance, cardiovascular stability, and overnight recovery following a four-hour thermoneutral HOWI on 12 subjects. Methods: Twelve males completed a crossover design consisting of no hydration, replacement of fluid loss during immersion (RD), and replacement of fluid after the immersion period (RA). Sixty minutes following immersion, subjects ran to exhaustion at ~80% maximum heart rate. After completing the run, each subject submitted to a head-up tilt test (HUTT). Vital signs and ECG were monitored overnight. Results: HOWI resulted in a transient diuresis in NH and RA, while it was sustained throughout immersion in the RD protocol, resulting in greater urine [l] output (1.27 ± 0.48 (NH), 1.18 ± 0.43 (RA), 2.32 ± 0.77 (RD) (p ⟨ 0.001). Body mass change (%) was greater in NH than RD, but not RA (-1.58 ± 0.56 (NH), -0.66 ± 0.47 (RD), and -0.92 ± 0.76 (RA)). Run times were 17% versus 20% in NH compared to RD and RA, respectively, but were not statistically different. Time to orthostasis during the HUTT did not differ by condition. Overnight heart rate variability and blood pressures were not different. Conclusion: Rehydration during water immersion resulted in a large, sustained diuresis without improving performance or recovery after exiting the water. Loss of body water during thermoneutral HOWI was modest, and both rehydration strategies minimally affected aerobic performance and overnight recovery in young, healthy males.

Effect of wetted surface area on friction, pressure, wave and total drag of a kayak.

Using theoretical principles, the components of drag (friction D F, pressure D PR and wave D W) of a single-seat kayak were analysed. The purpose was to examine the effect of changes in wetted surface area due to changes in kayaker's weight and the relative contribution of D F, D PR and D W to the total passive drag as function of velocity. The total passive drag values were based on experimental data collected in a single-seat kayak. Three different kayaker simulated weights were tested - 65, 75 and 85 kg. D F was the drag component that contributed the greatest percentage (between 60 and 68% at 5.56 m/s the top velocity tested) to the total passive drag for all the velocities tested and simulated weights. D W was the most affected by the increase in kayaker's simulated weight, mainly when comparing 65/75 to 85 kg. Results support the importance of a kayak design selection that minimises the kayak's drag for the individual weight of the kayaker. Also, the results suggest that the path for better hydrodynamic kayak performance should seek changes that can reduce D F, D PR and D W with D F offering the most potential to reduce passive drag.

Comparison of Classical Kinematics, Entropy, and Fractal Properties As Measures of Complexity of the Motor System in Swimming.

The aim of this study was to compare the non-linear properties of the four competitive swim strokes. Sixty-eight swimmers performed a set of maximal 4 × 25 m using the four competitive swim strokes. The hip's speed-data as a function of time was collected with a speedo-meter. The speed fluctuation (dv), approximate entropy (ApEn) and the fractal dimension by Higuchi's method (D) were computed. Swimming data exhibited non-linear properties that were different among the four strokes (14.048 ≤ dv ≤ 39.722; 0.682 ≤ ApEn ≤ 1.025; 1.823 ≤ D ≤ 1.919). The ApEn showed the lowest value for front-crawl, followed by breaststroke, butterfly, and backstroke (P < 0.001). Fractal dimension and dv had the lowest values for front-crawl and backstroke, followed by butterfly and breaststroke (P < 0.001). It can be concluded that swimming data exhibits non-linear properties, which are different among the four competitive swimming strokes.

Respiratory Muscle Training and Exercise Endurance at Altitude.

BACKGROUND: Climbing and trekking at altitude are common recreational and military activities. Physiological effects of altitude are hypoxia and hyperventilation. The hyperventilatory response to altitude may cause respiratory muscle fatigue and reduce sustained submaximal exercise. Voluntary isocapnic hyperpnea respiratory muscle training (VIHT) improves exercise endurance at sea level and at depth. The purpose of this study was to test the hypothesis that VIHT would improve exercise time at altitude [3600 m (11,811 ft)] compared to control and placebo groups. METHODS: Subjects pedaled an ergometer until exhaustion at simulated altitude in a hypobaric chamber while noninvasive arterial saturation (Sao2), ventilation (VE), and oxygen consumption (Vo2) were measured. RESULTS: As expected, Sao2 decreased to 88 ± 4% saturation at rest and to 81 ± 2% during exercise, and was not affected by VIHT. VIHT resulted in a 40% increase in maximal training VE compared to pre-VIHT. Exercise endurance significantly increased 44% after VIHT (P = <0.001). Vo2 (30 ± 3 ml · kg(-1) · min(-1)) and heart rate (177 ± 10 bpm) did not change during exercise and were not affected by VIHT (P = 0.531). Pre-VIHT VE increased 21-27% during the initial 12 min of exercise, after which it decreased 17% at 17.7 ± 6.0 min. VE at altitude post-VIHT increased more (49%) for longer (21 min) and decreased less (11% at 25.4 ± 6.7 min). DISCUSSION: VIHT improved exercise time at altitude and sustained VE. This suggests that VIHT reduced respiratory muscle fatigue and would be useful to trekkers and military personnel working at altitude. Helfer S, Quackenbush J, Fletcher M, Pendergast DR. Respiratory muscle training and exercise endurance at altitutde. Aerosp Med Hum Perform. 2016; 87(8):704-711.

Do 5% changes around maximal lactate steady state lead to swimming biophysical modifications?

Our purpose was to examine the swimming biophysical responses at velocities (v) of 97.5, 100 and 102.5% of the maximal lactate steady state (MLSS). Ten elite female swimmers performed three-to-five 30-min constant tests at imposed paces to determine 97.5, 100 and 102.5%MLSS v. Gas exchange, blood lactate concentration ([La-]), stroke rate (SR) and v were determined during each test. The v values at 97.5, 100 and 102.5%MLSS were 1.21±0.07, 1.24±0.07 and 1.27±0.07m.s(-1), respectively. Oxygen uptake (V̇O2) and Pulmonary ventilation (V̇E) increased as function of v. SR and stroke length (v/SR=SL) increased as a function of v. All measured variables were constant as a function of time at 97.5%MLSS and 100%MLSS. At 102.5%MLSS SR increased (3.5%) and stroke length (SL) decreased (3.5%) as a function of time. While V̇O2 was constant at 102.5%MLSS, [La-] and V̇E increased as a function of time, suggesting hyperventilation, at v's of 97.5%MLSS and 100%MLSS swimmers completed the 30min swim in spite of decreased SL and increased SR. However, the decrease in SL and increased SF were accompanied by increased [La-] and V̇E and resulted in the inability of most swimmers to complete the 30min swim presumably due to fatigue at 102.5%MLSS.

Respiratory Muscle Training and Cognitive Function Exercising at Altitude.

BACKGROUND: Hiking and trekking often occur at altitudes up to 12,000 ft altitude. The hypoxia-induced hyperventilation at altitude paradoxically reduces arterial CO2 (Paco2). A reduction in Paco2 results in vasoconstriction of the blood vessels of the brain and thus in local hypoxia. The local hypoxia likely affects cognitive function, which may result in reduced performance and altitude accidents. Recent publications have demonstrated that voluntary isocapnic hyperventilatory training of the respiratory muscles (VIHT) can markedly enhance exercise endurance as it is associated with reduced ventilation and its energy cost. VIHT may be useful in blunting the altitude-induced hyperventilation leading to higher Paco2 and improved cognitive function. METHODS: This study examined the effects of VIHT, compared to control (C) and placebo (PVIHT) groups, on selected measures of executive functioning, including working memory and processing speed (i.e., Stroop Test, Symbol Digit Modalities Test, and Digit Span Forward) at simulated altitude up to 12,000 ft. Associated physiological parameters were also measured. RESULTS: The Digit Span Forward Test did not show improvements after VIHT in any group. The VIHT group, but not C or PVIHT groups, improved significantly (17-30%) on the Stroop Test. Similarly the VIHT group, but not the C and PVIHT groups, improved correct responses (26%) and number of attempts (24%) on the Symbol Digit Modalities Test. In addition, reaction time was also improved (16%). CONCLUSION: VIHT improved processing speed and working memory during exercise at altitude.

Cerebral Blood Flow During Treadmill Exercise Is a Marker of Physiological Postconcussion Syndrome in Female Athletes.

OBJECTIVE: Some patients with postconcussion syndrome (PCS) have reduced exercise capacity that may reflect altered central cardiorespiratory control. The purpose of this study was to evaluate control of cerebral blood flow (CBF) during exercise in females with PCS. SETTING: University Concussion Clinic. PARTICIPANTS: Nine female Division 1 collegiate team athletes with PCS (23 ± 6 years) and a reference group of 13 healthy female recreational aerobic athletes (21 ± 3 years). DESIGN: A prospective experimental study. All PCS athletes were compared with the reference group at the beginning of the study. Six of the PCS athletes were subsequently measured before and after a subsymptom threshold aerobic exercise treatment program. MAIN MEASURES: Exercise treadmill test during which blood pressure (BP), minute ventilation ((Equation is included in full-text article.)E), end-tidal CO2 (PETCO2), and CBF velocity (CBFV, by transcranial Doppler) were measured. RESULTS: Participants with PCS had significantly lower (Equation is included in full-text article.)E (by 18%) and greater PETCO2 (5%) and CBFV (14%) versus the reference group at similar workloads in association with appearance of symptoms and premature exercise cessation. Subthreshold exercise normalized (Equation is included in full-text article.)E, PETCO2, CBFV and exercise tolerance. Before treatment, PCS had low CO2 sensitivity that blunted their exercise ventilation. CO2 sensitivity and ventilation improved after exercise treatment. CONCLUSION: Some PCS patients have exercise intolerance due to abnormal CBF regulation that may be the result of concussion-induced altered sensitivity to CO2. Return of normal CBF control and exercise tolerance may be physiological markers of recovery from concussion.

Is passive drag dependent on the interaction of kayak design and paddler weight in flat-water kayaking?

Drag is one of the major factors that influences kayaking performance. To focus on the drag of the kayak's hull shape and the paddlers' weight per se, the passive drag (Dp) was measured on a flat-water sprint course for one paddler with added weights. Dp was measured by an electromechanical towing device using a load cell, at incremental and constant velocities from 2.78 to 5.56 m/s. Three kayaks of different sizes and shapes (Nelo® K1 Quattro-M, ML, and L) were used and the paddlers' body weight was adjusted with weights so the total paddler weight in the kayak was 65, 75, and 85 kg. The mean Dp increased by the power function of D = kv(n) (mean R(2) = .990; SD .006). The Dp went from 21.37 ± 1.29 N at 2.78 m/s to 89.32 ± 6.43 N at 5.56 m/s. For the two lighter weighted kayaks (65 and 75 kg), the lowest Dp was observed with different kayak sizes (M, ML, or L) depending on the target velocity. The manufacturers suggest that paddlers should select a kayak size according to their body weight to minimise drag; however, the results of this study suggest that target velocities, and thus competition distance should also be factored into kayak selection.

Human Physiology in an Aquatic Environment.

Water covers over 70% of the earth, has varying depths and temperatures and contains much of the earth's resources. Head-out water immersion (HOWI) or submersion at various depths (diving) in water of thermoneutral (TN) temperature elicits profound cardiorespiratory, endocrine, and renal responses. The translocation of blood into the thorax and elevation of plasma volume by autotransfusion of fluid from cells to the vascular compartment lead to increased cardiac stroke volume and output and there is a hyperperfusion of some tissues. Pulmonary artery and capillary hydrostatic pressures increase causing a decline in vital capacity with the potential for pulmonary edema. Atrial stretch and increased arterial pressure cause reflex autonomic responses which result in endocrine changes that return plasma volume and arterial pressure to preimmersion levels. Plasma volume is regulated via a reflex diuresis and natriuresis. Hydrostatic pressure also leads to elastic loading of the chest, increasing work of breathing, energy cost, and thus blood flow to respiratory muscles. Decreases in water temperature in HOWI do not affect the cardiac output compared to TN; however, they influence heart rate and the distribution of muscle and fat blood flow. The reduced muscle blood flow results in a reduced maximal oxygen consumption. The properties of water determine the mechanical load and the physiological responses during exercise in water (e.g. swimming and water based activities). Increased hydrostatic pressure caused by submersion does not affect stroke volume; however, progressive bradycardia decreases cardiac output. During submersion, compressed gas must be breathed which introduces the potential for oxygen toxicity, narcosis due to nitrogen, and tissue and vascular gas bubbles during decompression and after may cause pain in joints and the nervous system.

Effects of ambient temperature on nitrogen uptake and elimination in humans.

Tissue nitrogen (N2) exchange is primarily dependent on circulation, which may be modified by body thermal status. Thermal effects on uptake and washout of N2 have not been systematically investigated earlier. In the present study of eight subjects, N2 was washed out in thermally neutral ambient conditions (TN; skin temperature (Ts) = 33.69 ± 0.84 degrees C), then washed in during either TN, cool (Ts 30.25 ± 4.15 degrees C) or warm (Ts = 35.81 ± 0.82 degrees C) conditions. It was then washed out during various combinations of those conditions. N2 exchange was monitored during 125 minutes of breathing a normoxic oxygen/argon mixture (Phase I) followed by room air for 125 minutes of N2 reloading (Phase II; no N2 recording) and then 125 minutes N2 washout (Phase III) in order to determine the amount of N2 taken up during Phase II. Cool conditions reduced cardiac output, while warm conditions increased it compared to TN. Among the five Phase I TN recordings in the eight subjects (i.e., 40 control experiments) the N2 yield averaged 857.2 ± 15.3 mL. The reloaded N2 volume in Phase II was significantly smaller during the cool condition (8%, p ≤ 0.05) and significantly larger (22%, p ≤ 0.05) during the warm. The N2 washed out in 125 minutes was significantly less during cold (6%, p ≤ 0.05) and greater during warm conditions (18%, p ≤ 0.05). These observations are consistent with previously reported circulatory changes in cool and warm conditions and effects of thermal status on venous gas bubble dynamics and incidents of decompression sickness.

Electrocardiogram at an altitude of 3600 m with reference to T wave depression.

INTRODUCTION: Exposure to high altitude decreases arterial oxygen saturation (Sa(O2)). Previous studies have shown decreased voltage of the T wave of the electrocardiogram (ECG) at altitudes up to 7000 m (22,966 ft) secondary to hypoxia. This pilot study explored changes in the ECG at the maximum altitude pilots can fly without supplemental oxygen. In addition, this is a common altitude for recreational trekkers. METHODS: There were 13 subjects who rested at sea level (1ATA) for 30 min and then were taken to an altitude of 3000 m or 3600 m (10,000 or 12,000 ft; at altitude) where they rested for 30 min. ECG was collected continuously as was Sa(O2) and heart rate (HR). A series of 10 ECG complexes were analyzed for 7 time periods over the 30-min collection periods. RESULTS: The P wave, PR, QRS, and QT interval duration did not show a significant difference between 1 ATA and at altitude for the group of subjects analyzed (N = 11 ). The T wave amplitude showed a significant decrease (delta = -19.3%) for seven subjects at altitude; however, the other six subjects did not show a significant change (delta = 1.6%). The T wave amplitude observations described above were consistent for average HRs and selected HRs that were equal between 1 ATA and at altitude. CONCLUSION: This study confirmed that some subjects showed decreased T wave amplitude at altitude which was not associated with pulmonary function, HR, ventilation, end-tidal CO2, or Sa(O2).

The effects of respiratory muscle training on respiratory mechanics and energy cost.

Resistance respiratory muscle training (RRMT) increases respiratory muscle strength and can increase swimming endurance time by as much as 85%. The purpose of this study was to examine potential mechanisms by which RRMT improves exercise endurance. Eight healthy adult male scuba divers underwent experiments in a hyperbaric chamber at sea level (1 atmosphere absolute (ATA)), 2.7 ATA and 4.6 ATA, both dry and fully submersed. Subjects rested, exercised, and rested while mimicking their own exercise breathing (ISEV). Airway resistance (R(aw)), exhaled nitric oxide output (V˙(NO)), and respiratory duty cycle (T(I)/T(Tot)) were determined before and after four weeks of RRMT. RRMT decreased T(I)/T(Tot) (-10% at rest at 1 ATA), V˙(O2) (-17% at 2.7 ATA during submersed exercise), V˙(E) (-6% at 2.7 ATA during submersed exercise), and R(aw) (-34% inspiratory at 4.6 ATA submersed, -38% expiratory at 2.7 ATA dry), independent of changes in V˙(NO). Most importantly, respiratory muscle efficiency increased (+83% at 2.7 ATA submersed).

Critical evaluation of oxygen-uptake assessment in swimming.

Swimming has become an important area of sport science research since the 1970s, with the bioenergetic factors assuming a fundamental performance-influencing role. The purpose of this study was to conduct a critical evaluation of the literature concerning oxygen-uptake (VO2) assessment in swimming, by describing the equipment and methods used and emphasizing the recent works conducted in ecological conditions. Particularly in swimming, due to the inherent technical constraints imposed by swimming in a water environment, assessment of VO2max was not accomplished until the 1960s. Later, the development of automated portable measurement devices allowed VO2max to be assessed more easily, even in ecological swimming conditions, but few studies have been conducted in swimming-pool conditions with portable breath-by-breath telemetric systems. An inverse relationship exists between the velocity corresponding to VO2max and the time a swimmer can sustain it at this velocity. The energy cost of swimming varies according to its association with velocity variability. As, in the end, the supply of oxygen (whose limitation may be due to central-O2 delivery and transportation to the working muscles-or peripheral factors-O2 diffusion and utilization in the muscles) is one of the critical factors that determine swimming performance, VO2 kinetics and its maximal values are critical in understanding swimmers' behavior in competition and to develop efficient training programs.

Negative pressure breathing increases cardiac output and nitrogen elimination in seated subjects.

During denitrogenation for rescue, crew members of an internally pressurized disabled submarine (DISSUB) must sit upright, which may hamper venous return, cardiac output and peripheral circulation. Since negative pressure breathing (NPB) might counteract this problem, denitrogenation was measured in sitting subjects performing NPB. Seven male subjects completed 125-minute nitrogen (N2) washouts breathing either 100% oxygen (O2) or a normoxic gas (21% O2 in argon) in control conditions and intermittent (I: inspirations only) or continuous (C) NPB at -10 or -15 cmH2O. N2 elimination was measured using a closed rebreathing system. INPB (intermittent) (-15cmH2O) and CNPB (continous breathing) (-10 and -15cmH2O) increased cardiac output (CO) 9% during both O2 and normoxic breathing. Systolic and diastolic blood pressures were unaffected by the CO increase, suggesting a peripheral vasodilatation and enhanced tissue perfusion leading to increased N2 elimination. With the CO boost, N2 washout increased 6% breathing O2 at -15 cmH2O CNPB and INPB, while during normoxic breathing there were 6% and 12% increases due to CNBP, -10 and -15 respectively and 6% with -15cmH2O INPB; breathing 100% O2 yielding 5% to 15% less N2 washout than normoxic breathing. Negative pressure breathing during denitrogenation may facilitate decompression in divers and in crew members being rescued from a DISSUB.

Interplay of biomechanical, energetic, coordinative, and muscular factors in a 200 m front crawl swim.

This study aimed to determine the relative contribution of selected biomechanical, energetic, coordinative, and muscular factors for the 200 m front crawl and each of its four laps. Ten swimmers performed a 200 m front crawl swim, as well as 50, 100, and 150 m at the 200 m pace. Biomechanical, energetic, coordinative, and muscular factors were assessed during the 200 m swim. Multiple linear regression analysis was used to identify the weight of the factors to the performance. For each lap, the contributions to the 200 m performance were 17.6, 21.1, 18.4, and 7.6% for stroke length, 16.1, 18.7, 32.1, and 3.2% for stroke rate, 11.2, 13.2, 6.8, and 5.7% for intracycle velocity variation in x, 9.7, 7.5, 1.3, and 5.4% for intracycle velocity variation in y, 17.8, 10.5, 2.0, and 6.4% for propelling efficiency, 4.5, 5.8, 10.9, and 23.7% for total energy expenditure, 10.1, 5.1, 8.3, and 23.7% for interarm coordination, 9.0, 6.2, 8.5, and 5.5% for muscular activity amplitude, and 3.9, 11.9, 11.8, and 18.7% for muscular frequency). The relative contribution of the factors was closely related to the task constraints, especially fatigue, as the major changes occurred from the first to the last lap.

Relative effects of submersion and increased pressure on respiratory mechanics, work, and energy cost of breathing.

Submersion and increased pressure (depth) characterize the diving environment and may independently increase demand on the respiratory system. To quantify changes in respiratory mechanics, this study employed a unique protocol and techniques to measure, in a hyperbaric chamber, inspiratory and expiratory alveolar pressures (interrupter technique), inspiratory and expiratory resistance in the airways (RawI and RawE, esophageal balloon technique), nitric oxide elimination (thought to correlate with Raw), inspiratory and expiratory mechanical power of breathing, and the total energy cost of ventilation. Eight healthy adult men underwent experiments at 1, 2.7, and 4.6 atmospheres absolute (ATA) in dry and fully submersed conditions. Subjects rested, cycled on an ergometer at 100 W, and rested while voluntarily matching their ventilation to their own exercise hyperpnea (isocapnic simulated exercise ventilation). During isocapnic simulated exercise ventilation, increased O2 uptake (above rest values) resulted from increased expired ventilation. RawI decreased with submersion (mean 43% during rest and 20% during exercise) but increased from 1 to 4.6 ATA (19% during rest and 75% during exercise), as did RawE (53% decrease with submersion during rest and 10% during exercise; 9% increase from 1 to 4.6 ATA during rest and 66% during exercise). Nitric oxide elimination did not correlate with Raw. Depth increased inspiratory mechanical power of breathing during rest (40%) and exercise (20%). Expiratory mechanical power of breathing was largely unchanged. These results suggest that the diving environment affects ventilatory mechanics primarily by increasing Raw, secondary to increased gas density. This necessitates increased alveolar pressure and increases the work and energy cost of breathing as the diver descends. These findings can inform physician assessment of diver fitness and the pulmonary risks of hyperbaric O2 therapy.

Exercise treatment for postconcussion syndrome: a pilot study of changes in functional magnetic resonance imaging activation, physiology, and symptoms.

PURPOSE: To compare functional magnetic resonance imaging (fMRI) activation patterns during a cognitive task, exercise capacity, and symptoms in postconcussion syndrome (PCS) patients who received exercise treatment (n = 4) with a PCS placebo stretching group (n = 4) and a healthy control group (n = 4). METHODS: Subjects completed a math processing task during fMRI and an exercise treadmill test before (time 1) and after approximately 12 weeks (time 2). Exercise subjects performed aerobic exercise at 80% of the heart rate (HR) attained on the treadmill test, 20 minutes per day with an HR monitor at home, 6 days per week. The program was modified as the HR for symptom exacerbation increased. RESULTS: At time 1, there was no difference in fMRI activation between the 2 PCS groups but healthy controls had significantly greater activation in the posterior cingulate gyrus, lingual gyrus, and cerebellum versus all PCS subjects (P < .05, corrected for multiple comparisons). At time 2, exercise PCS did not differ from healthy controls whereas placebo stretching PCS had significantly less activity in the cerebellum (P < .05 corrected) and in the anterior cingulate gyrus and thalamus (P < .001, uncorrected) versus healthy controls. At time 2, exercise PCS achieved a significantly greater exercise HR (P < .001) and had fewer symptoms (P < .0004) than placebo stretching PCS. Cognitive performance did not differ by group or time. CONCLUSIONS: Controlled aerobic exercise rehabilitation may help restore normal cerebral blood flow regulation, as indicated by fMRI activation, in PCS patients. The PCS symptoms may be related to abnormal cerebral blood flow regulation.

Effects of different types of respiratory muscle training on exercise performance in runners.

To compare two different types of respiratory muscle training on exercise performance, a protocol was devised consisting of a combination of a 4-week, 12-session resistive respiratory muscle training (RRMT) followed by a 4-week, 12-session voluntary isocapnic hyperpnea training (VIHT) and conducted in experienced runners (4 men, 4 women). Measurements before and 5 days after training included: pulmonary function (spirometry), maximal inspiratory and expiratory mouth pressures, respiratory endurance time, maximal oxygen uptake (V(o2)max), running time to voluntary exhaustion at 80% V(o2)max, blood lactate concentration, and minute ventilation. There were no statistically significant differences in pulmonary functions and V(o2)max post-RRMT and post-VIHT compared to pre-RMT. Following RRMT the inspiratory muscle strength had improved by 23.8 +/- 30% and 18.7 +/- 21.4% at rest and immediately after the running test, respectively. RRMT did not increase the time intense voluntary isocapnic ventilation could be maintained during rest while VIHT increased it (237 +/- 207.8%). The duration of the endurance run was extended 17.7 +/- 6.5% after RRMT and 45.5 +/- 14.3% after VIHT.