Type 1 Diabetes Duration Decreases Pulmonary Diffusing Capacity during Exercise.

BACKGROUND: Diabetes damages peripheral tissues; however, its effects on the lung are less known. Lung diffusing capacity (DLCO) is influenced by alveolar-capillary membrane conductance (DM) and pulmonary capillary blood volume (VC), both of which are reduced in adults with type 1 diabetes (T1D). OBJECTIVE: We sought to determine if diabetes duration affects DLCO, DM, VC, and cardiac output (Q). METHODS: 24 T1D patients (10.7-52.8 years) and 24 non-diabetic controls were recruited and had DLCO, DM, VC, and Q measured at rest and during exercise (40, 70 and 90% VO2max). RESULTS: When stratified into two groups based on age (young, <20.6 years old), there were no significant differences in DLCO, DM, VC, or Q (all of which were normalized to body surface area [BSA]) in the young group or in the old group. When stratified by diabetes duration (short duration, 0.33-8.9 years vs. long duration, 9.6-28 years), the T1D patients in the long duration group had lower DLCO/BSA and DM/BSA compared to the controls (p < 0.05). There were no differences in any of the variables in the short duration group. CONCLUSIONS: This study has shown that duration of diabetes is associated with decrements in diffusing capacity and its components.

Oxygen consumption of elite distance runners on an anti-gravity treadmill®.

Lower body positive pressure (LBPP), or 'anti-gravity' treadmills® have become increasingly popular among elite distance runners. However, to date, few studies have assessed the effect of body weight support (BWS) on the metabolic cost of running among elite runners. This study evaluated how BWS influenced the relationship between velocity and metabolic cost among 6 elite male distance runners. Participants ran three- 16 minute tests consisting of 4 stages of 4 minutes at 8, 7, 6 and 5 min·mile(-1) pace (3.35, 3.84, 4.47 and 5.36 m·s(-1)), while maintaining an aerobic effort (Respiratory Exchange Ratio ≤1.00). One test was run on a regular treadmill, one on an anti-gravity treadmill with 40% BWS and one with 20% BWS being provided. Expired gas data were collected and regression equations used to determine and compare slopes. Significant decreases in oxygen uptake (V̇O2) were found with each increase in BWS (p < 0.001). At 20% BWS, the average decrease in net VO2 was greater than proportional (34%), while at 40% BWS, the average net reduction in VO2 was close to proportional (38%). Across velocities, the slope of the relationship between VO2 and velocity (ΔV̇O2/Δv) was steeper with less support. The slopes at both the 20% and 40% BWS conditions were similar, especially when compared to the regular treadmill. Variability in VO2 between athletes was much greater on the LBPP treadmill and was greater with increased levels of BWS. In this study we evaluated the effect of body weight support on V̇O2 among elite distance runners. We have shown that oxygen uptake decreased with support, but not in direct proportion to that support. Further, because of the high variability in oxygen uptake between athletes on the LBPP treadmill, prediction equations may not be reliable and other indicators (heart rate, perceived exertion or directly measured oxygen uptake) should be used to guide training intensity when training on the LBPP treadmill. Key pointsWith increasing amounts of body weight-support (BWS), the slope of the relationship between velocity and oxygen consumption (ΔVO2/Δv) decreases significantly. This means the change in oxygen consumption (VO2) is significantly smaller over a given change in velocity at higher amounts of BWS.There is a non-linear decrease in VO2 with increasing BWS. As such, with each increment in the amount of BWS provided, the reduction in VO2 becomes increasingly smaller.This paper provides first of its kind data on the effects of BWS on the cost of running among highly trained, elite runners. The outcomes of this study are in line with previous findings among non-elite runners.

Accuracy of unloading with the anti-gravity treadmill.

Body weight (BW)-supported treadmill training has become increasingly popular in professional sports and rehabilitation. To date, little is known about the accuracy of the lower-body positive pressure treadmill. This study evaluated the accuracy of the BW support reported on the AlterG "Anti-Gravity" Treadmill across the spectrum of unloading, from full BW (100%) to 20% BW. Thirty-one adults (15 men and 16 women) with a mean age of 29.3 years (SD = 10.9), and a mean weight of 66.55 kg (SD = 12.68) were recruited. Participants were weighed outside the machine and then inside at 100-20% BW in 10% increments. Predicted BW, as presented by the AlterG equipment, was compared with measured BW. Significant differences between predicted and measured BW were found at all but 90% through 70% of BW. Differences were small (<5%), except at the extreme ends of the unloading spectrum. At 100% BW, the measured weight was lower than predicted (mean = 93.15%, SD = 1.21, p < 0.001 vs. predicted). At 30 and 20% BW, the measured weight was higher than predicted at 35.75% (SD = 2.89, p < 0.001), and 27.67% (SD = 3.76, p < 0.001), respectively. These findings suggest that there are significant differences between reported and measured BW support on the AlterG Anti-Gravity Treadmill®, with the largest differences (>5%) found at 100% BW and the greatest BW support (30 and 20% BW). These differences may be associated with changes in metabolic demand and maximum speed during walking or running and should be taken into consideration when using these devices for training and research purposes.

Is lung diffusing capacity lower in expiratory flow limited women compared to non-flow limited women during exercise?

PURPOSE: Women tend to have smaller lungs than men of the same size as well as narrower airways compared to men when matched for the same lung size. Additionally, women with smaller airways relative to lung size are more likely to experience expiratory flow limitation (EFL) as well as exercise-induced arterial hypoxemia (EIAH). One of the possible causes of EIAH includes excessive widening in the alveolar-to-arterial oxygen pressure difference (A-aDO2) due to diffusion limitation. This study investigated if lung diffusing capacity (D LCO) is lower in women with EFL compared to non-flow limited (NEFL) women during exercise. METHODS: D LCO was measured using the rebreathing technique at rest and at 40, 60, and 80 % of [Formula: see text] on a treadmill in healthy women with EFL (n = 7; 21.6 ± 2.3) and without EFL (NEFL, n = 9; 21.2 ± 2.3). Arterial oxygen saturation was measured using pulse oximetry (SpO2). RESULTS: There was no difference (p > 0.05) in D LCO between groups at rest or during exercise; however, SpO2 was significantly lower in the EFL females compared to NEFL females during exercise. CONCLUSION: Due to the lack of differences in D LCO between women with EFL and without EFL, our results suggest that this is not a possible cause for the significant differences in SpO2 between the two groups.

Metabolic accommodation to running on a body weight-supported treadmill.

PURPOSE: Body weight-supported treadmill training using positive air pressure has become increasingly popular, but little is known about the metabolic adaptations to these treadmills. This study aimed to evaluate the existence and length of a metabolic accommodation period to running on a lower body positive pressure (LBPP) treadmill. METHODS: A total of eight recreational runners (5 males and 3 females) ran 15 min trials (5 min at 50, 70, and 90 % body weight) on the AlterG Anti-gravity(®) P200 treadmill. No verbal instruction was given on how to run on the device. Their trial pace corresponded to 70-80 % of their velocity measured at [Formula: see text]O2max on a standard treadmill. Trials were continued until no significant metabolic change was observed. Two-way repeated measures analysis of variance was used to analyze changes in [Formula: see text]O2 across trials and levels of unloading. RESULTS: Participants completed 7 trials. Comparing trial 1 to the average of trials 5, 6, and 7, [Formula: see text]O2 decreased from 29.6 ± 3.8 to 23.6 ± 4.4 ml/kg/min at 50 % body weight (~20 % reduction), from 33.7 ± 4.5 to 29.2 ± 5.1 ml/kg/min at 70 % body weight (~13 % reduction), and from 41.0 ± 7.7 to 36.6 ± 5.6 ml/kg/min at 90 % body weight (~11 % reduction). No significant reduction occurred after trial 4 at any level of support. CONCLUSIONS: An accommodation effect of running on a treadmill with LBPP was observed and reached after 60 min of running (4 trials of 15 min). The accommodation effect was the largest at the greatest level of body weight support. These data suggest the importance of an accommodation period for reliable measures of metabolic cost to be made.

Conversion table for running on lower body positive pressure treadmills.

Lower body positive pressure (LBPP) or antigravity treadmills are becoming increasingly popular in sports and rehabilitation settings. Running at a decreased body weight (BW) reduces metabolic cost, which can be offset by running at faster speeds. To date, however, little is known about how much faster someone must run to offset the reduced metabolic cost. This study aimed to develop a user-friendly conversion table showing the speeds required on an LBPP treadmill to match the equivalent metabolic output on a regular, non-LBPP, treadmill across a range of body weight supports. A total of 20 recreational runners (11 males, 9 females) ran multiple 3-minute intervals on a regular treadmill and then on an LBPP treadmill at 6 different BWs (50-100%, 10% increments). Metabolic outputs were recorded and matched between the regular and LBPP treadmill sessions. Using regression analyses, a conversion table was successfully created for the speeds from 6.4 to 16.1 km·h (4 to 10 mph) in 0.8 km·h (0.5 mph) increments on the regular treadmill and BW proportions of 50, 60, 70, 80, 90, and 100% on an LBPP treadmill. The table showed that a greater increase in speed on the LBPP treadmill was needed with more support (p < 0.001) but that the proportion increase was smaller at higher speeds (p < 0.001). This research has implications for coaches or practitioners using or prescribing training on an LBPP treadmill.

Comparison of force exerted on the sternum during a sneeze versus during low-, moderate-, and high-intensity bench press resistance exercise with and without the valsalva maneuver in healthy volunteers.

Sternal precautions are intended to prevent complications after median sternotomy, but little data exist to support the consensus recommendations. To better characterize the forces on the sternum that can occur during everyday events, we conducted a prospective nonrandomized study of 41 healthy volunteers that evaluated the force exerted during bench press resistance exercise and while sneezing. A balloon-tipped esophageal catheter, inserted through the subject's nose and advanced into the thoracic cavity, was used to measure the intrathoracic pressure differential during the study activities. After the 1 repetition maximum (1-RM) was assessed, the subject performed the bench press at the following intensities, first with controlled breathing and then with the Valsalva maneuver: 40% of 1-RM (low), 70% of 1-RM (moderate), and 1-RM (high). Next, various nasal irritants were used to induce a sneeze. The forces on the sternum were calculated according to a cylindrical model, and a 2-tailed paired t test was used to compare the mean force exerted during a sneeze with the mean force exerted during each of the 6 bench press exercises. No statistically significant difference was found between the mean force from a sneeze (41.0 kg) and the mean total force exerted during moderate-intensity bench press exercise with breathing (41.4 kg). In conclusion, current guidelines and recommendations limit patient activity after a median sternotomy. Because these patients can repeatedly withstand a sneeze, our study indicates that they can withstand the forces from more strenuous activities than are currently allowed.

Maximal respiratory pressure reference values for Navajo children ages 6-14.

BACKGROUND: Since anthropometric variables are critical to the creation of pulmonary nomograms for FVC, FEV1, and other volumes and capacities, it is logical that anthropometric variables also influence the values of the maximal respiratory pressures (MRPs). Since nomograms are race-specific, it is important that tribe-specific tables of normal maximal inspiratory pressure (MIP) and maximal expiratory pressure (MEP) be developed. To date normal tables for MRPs do not exist for Navajo children. OBJECTIVE: Therefore the purpose of this study was to derive MRP normative reference values for Navajo children in the age range of 6-14 years. METHODS-PARTICIPANTS AND MEASUREMENTS: A cross-sectional study was undertaken with a representative sample of 534 healthy children, ages 6-14 years, attending Navajo Nation elementary schools in Arizona. MIP and MEP were measured. RESULTS: Test results from 275 girls and 259 boys met American Thoracic Society quality control standards and showed that MRPs all increased with height. Mean MIP in cm H2 O was 77 for boys and 67 for girls with lower limits of 44 and 40, respectively. Mean MEP in cm H2 O was 75 for boys and 66 for girls with the lower limits of 42 and 38, respectively. CONCLUSION: Since the data were collected from the population of interest, the resulting MIP and MEP reference equations should be used when testing Navajo children ages 6-14 years.

The effect of core exercises on transdiaphragmatic pressure.

Abdominal exercises, such as sit ups and leg lifts, are used to enhance strength of the core muscles. An overlooked aspect of abdominal exercises is the compression the abdomen, leading to increased diaphragmatic work. We hypothesized that core exercises would produce a variety of transdiaphragmatic pressures. We also sought to determine if some of the easy exercises would produce pressures sufficient for a training stimulus to the diaphragm. We evaluated the effect of 13 different abdominal exercises, ranging in difficulty, on transdiaphragmatic pressure (Pdi), an index of diaphragmatic activity. Six healthy subjects, aged 22 to 53, participated. Each subject was instrumented with two balloon-tipped catheters to obtain gastric and esophageal pressures, from which Pdi was calculated. Prior to initiating the exercises, each subject performed a maximal inspiratory pressure (MIP) maneuver. Resting Pdi was also measured. The exercises were performed from least to most difficult, with five repetitions each. There was a significant difference between the exercises and the MIP Pdi, as well as between the exercises and resting Pdi (p < 0.001). The exercises stratified into three Pdi levels. Seven of the exercises yielded Pdi ≥ 50% of the Pdi during the MIP maneuver, which may provide a training stimulus to the diaphragm if used as a regular exercise. The Pdi measurements also provide insight into diaphragm recruitment during different core exercises, and may aid in the design of exercises to improve diaphragm strength and endurance. Key pointsPlease provide 3-5 bullet points of the study.The study examined the effect of different core exercises of varying difficulty on activation of the diaphragm.We found that the exercises yielded different pressures, some of which were greater than 50% of the pressures generated during a maximal inspiratory maneuver.The difficulty of the exercise was not always correlated with the magnitude of the pressure.Some of these exercises should be easy enough for subjects in rehabilitation programs to perform and still generate high enough pressures to help strengthen the diaphragm.

Spirometry reference values for Navajo children ages 6-14 years.

Spirometry is the most important tool in diagnosing pulmonary disease and is the most frequently performed pulmonary function test. Since respiratory disease is the single greatest cause for morbidity and mortality on the Navajo Nation, the purpose of this study was to create new age and race-specific pulmonary nomograms for Navajo children. Five hundred fifty-eight healthy children, ages 6-14 years, attending Navajo Nation elementary schools in Arizona, were asked to perform spirometry to develop population-specific and tribe-specific nomograms for forced vital capacity (FVC), forced expiratory volume in 1 sec (FEV1), and FEV1 Ratio (FEV1/FVC). Spirometry tests from 284 girls and 274 boys met American Thoracic Society quality control standards. Lung function values, except for FEV1/FVC, all increased with height. The lower limit of the normal range for FEV1/FVC was 80%. The spirometry reference equations from the healthy boys and girls were developed. Height and the natural log of height were significant predictors of FEV1, FVC, and FEF(25-75%) in the gender-specific models. The resulting population-specific spirometry reference equations should be used when testing Navajo children ages 6-14 years. However, the use of the NHANES III spirometry reference equations for Caucasian children may not result in significant misclassification in clinical settings providing that a maximal effort is given by the Navajo child being tested.

Repeated abdominal exercise induces respiratory muscle fatigue.

Prolonged bouts of hyperpnea or resisted breathing are known to result in respiratory muscle fatigue, as are primarily non respiratory exercises such as maximal running and cycling. These exercises have a large ventilatory component, though, and can still be argued to be respiratory activities. Sit-up training has been used to increase respiratory muscle strength, but no studies have been done to determine whether this type of non-respiratory activity can lead to respiratory fatigue. The purpose of the study was to test the effect of sit-ups on various respiratory muscle strength and endurance parameters. Eight subjects performed pulmonary function, maximum inspiratory pressure (MIP) and maximum expiratory pressure (MEP) measurements, and an incremental breathing test before and after completing a one-time fatiguing exercise bout of sit-ups. Each subject acted as their own control performing the same measurements 3-5 days following the exercise bout, substituting rest for exercise. Following sit-up induced fatigue, significant decreases were measured in MIP [121.6 ± 26 to 113.8 ± 23 cmH2O (P <0.025)], and incremental breathing test duration [9.6 ± 1.5 to 8.5 ± 0.7 minutes (P <0.05)]. No significant decreases were observed from control pre-test to control post-test measurements. We conclude that after a one-time fatiguing sit-up exercise bout there is a reduction in respiratory muscle strength (MIP, MEP) and endurance (incremental breathing test duration) but not spirometric pulmonary function. Key pointsExercise that is primarily abdominal in nature can lead to inspiratory muscle fatigue.This exercise also can cause expiratory muscle fatigue, which would be expected.This study shows a link between a predominantly non-respiratory exercise and decreases in both respiratory muscle strength and endurance.

Obesity and pulmonary function in Navajo and Hopi children.

BACKGROUND: Although several reports have shown an adverse cardiovascular and metabolic risk profile associated with childhood obesity, few reports have examined the effects of childhood obesity on pulmonary function. OBJECTIVE: The purpose of this study was to examine the influence of obesity on pulmonary function in Navajo and Hopi children. METHODS: Subjects included 256 (110 males, 146 females) Hopi children 6-12 years of age and 557 (274 males, 283 females) Navajo children 6-12 years of age (N = 813). The body mass index was used to classify subjects as normal weight, overweight, or obese on the basis of international reference values. Forced vital capacity (FVC), forced expired volume in one second (FEV1), FEV1% (FEV1 to FVC ratio; FEV1/FVC), and forced expiratory flow between 25%-75% of vital capacity (FEF25-75) were determined according to the American Thoracic Society recommendations. RESULTS: Approximately 26% of Navajo and Hopi children were defined as overweight additional 16% (14.6% of boys and 17.7% of girls) were defined as obese. In general, the patterns showed an increase in pulmonary function between normal weight and overweight children and a decrease in pulmonary function of obese children. Significant differences among groups existed for FEV1% and FEF25-75 in boys and FVC and FEV1 in girls. CONCLUSIONS: The results indicate the pulmonary consequences of obesity in children and provide further evidence of the adverse consequences of pediatric obesity among Native Americans.

Zidovudine-induced diaphragmatic contractile dysfunction: impact of an antioxidant diet.

OBJECTIVE: Zidovudine (AZT) is a primary drug therapy used to treat HIV-infected individuals. While AZT inhibits replication of HIV, it also induces a drug-specific myopathy resulting in altered muscle mitochondria, increased oxidative stress and muscle contractile dysfunction. The purpose of this study was to assess the impact of an antioxidant diet (high in vitamins C and E) on AZT-mediated diaphragmatic contractile dysfunction in rodents. METHODOLOGY: Adult, Sprague-Dawley rats were assigned to feeding groups: control (CON, n = 9), AZT-treatment (AZT, n = 8), antioxidant diet only (Anti-Ox, n = 6), and AZT + antioxidant diet (AZT + Anti, n = 9). Two costal diaphragm strips were removed from each animal (under surgical anaesthesia) and evaluated for force-frequency relationship, maximal specific tension, and fatigue resistance using an in vitro preparation. RESULTS: Results indicate significant reductions in normalized force production (20-200 Hz), including maximal specific tension, between AZT animals and all other groups. While AZT reduced diaphragm contractility, the addition of an antioxidant diet eliminated this decrease. CONCLUSION: These data suggest that an increase in oxidative stress mediated by AZT may contribute to AZT-induced muscle contractile dysfunction, and that antioxidant vitamin supplementation may help ameliorate this effect.

Spinal cord injury and contractile properties of the human tibialis anterior.

The purpose of this study was to evaluate contractile properties of the tibialis anterior of paralyzed and non-paralyzed subjects. The contractile properties and the fatigability of the tibialis anterior muscle (TA) were tested in 8 spinal cord injured (SCI) and 8 control individuals. The TA was stimulated at frequencies from 10 to 100 Hz to determine a force-frequency curve. A fatigue bout was also performed by stimulating the muscle at 40 Hz every two seconds for three minutes. The SCI muscles produced lower forces overall, but higher forces relative to maximal force at lower frequencies, shifting the force-frequency curve of the SCI group to the left. The half-relaxation time and rate of relaxation at 40 Hz was slower in the SCI muscles than in the control muscles (127 ± 18.4 ms vs. 78 ± 8.7 ms, 6 ± 1.5 kg·s(-1) 20 ± 4.1 kg·s(-1) respectively). In addition, force loss and slowing of relaxation during the fatigue protocol were not significantly different between the two groups due to high variability in the SCI group. The TA of the SCI group had slower contractile properties than the control group and fatigability was not significantly different between the SCI and control group. The protocol may be useful to assess training effects during rehabilitation of paralyzed muscle. Key PointsStimulated contractions were tested on controls and spinal cord injured subjects to determine differences in contractile characteristics of the tibialis anterior (ta) muscle.Forces were lower in the ta of the spinal cord injured subjects compared to the controls.All indices of contractile speed were slower in the spinal cord injured subjects than in the controls.The reason for possible differences in contractile capabilities and other biochemical indices of contractile speed in disused muscle need to be further evaluated.

The effect of football shoulder pads on pulmonary function.

Restriction of expansion of the lungs or chest wall impedes inflation of the lungs during inhalation. Functional changes occurring during such restriction include reduced pulmonary and/or chest wall compliance, decreases in pulmonary function, and ultimately a decrease in exercise performance. Such restriction can be seen in several pathologic conditions such as scoliosis or obesity, as well as occupational situations such as the wearing of bullet-proof vests. This study investigated the hypothesis that tightened football shoulder pads produce decrements in pulmonary function similar to those shown in previous studies involving other external chest-wall restricting devices. In this study, 24 subjects, all members of a collegiate division IAA football team and used to wearing the pads, performed standard pulmonary function tests while wearing no pads (control, CTRL), wearing pads that were not secured (pads loose, PL) and while wearing pads secured "game-tight" (pads tight, PT). The data showed that both forced vital capacity (FVC) and forced expiratory volume in one second (FEV1.0) were significantly decreased in the PT condition compared to either the CTRL or PL condition, with no changes in the FEV1.0/FVC ratio or peak expiratory flow rate. These results are consistent with a restrictive condition and support our hypothesis that tightened shoulder pads reduce pulmonary function. Further studies remain to be performed to determine whether these changes lead to decreased exercise performance and whether equipment modifications can be made to limit alterations in pulmonary function without decreasing the protective value of the pads. Key PointsThe shoulder pads used in American football extend to the xyphoid process and may provide a restriction to breathing. This was tested in the present study in 24 college-level football players with normal resting pulmonary function.The results showed that there was a decrease in FVC of approximately 150 ml and a similar decrease in FEV1.0.Similar decreases in pulmonary function have been shown to provide a limitation to exercise capacity in otherwise healthy adults.Further study is needed to determine whether these changes lead to decrements in performance.

The effect of chest wall restriction on exercise capacity.

OBJECTIVE: Subjects with restrictive pulmonary disease exhibit a decreased exercise capacity compared to non-diseased subjects, as do subjects in certain workplace situations, for example when wearing bullet-proof vests. The purpose of this study was to examine the effects of varying degrees of chest wall restrictive loading on exercise performance. We have designed and validated a chest wall restrictor that mimics the elastic loading occurring in some disease states and some occupational situations. METHODOLOGY: In this study, 18 subjects performed five graded maximal cycling tests while wearing the device at four different inflation pressures (0, 20, 40, and 60 mmHg). RESULTS: Maximal values of oxygen uptake (VO2max), minute ventilation (VImax), tidal volume (VT at max) and breathing frequency (fB at max) were monitored, as was the time to maximal exercise (TTM). VO2, VI, VT, and fB were also measured at three submaximal loads. The results showed that VO2max, VImax, TTM, and VT at max were significantly decreased, while fB at max was maintained. At submaximal loads, the ventilatory parameters VT, and fB were altered with load, but VI and VO2 were not affected by load. CONCLUSIONS: These results indicate that the wearing of this device decreases variables associated with maximal exercise, and that the decreases are related to the degree of chest wall restriction. Furthermore, submaximal exercise ventilation was minimally altered, with an increase in fB and a decrease in VT associated with increasing restrictive loads. Submaximal oxygen uptake was not affected by breathing restriction.

Do gender differences in running performance disappear with distance?

It has been suggested that gender differences in running should disappear as distances increase, particularly past the marathon. This suggestion is primarily based on differences in fuel utilization, muscle damage following exercise, relative improvements in performance over the past decades, and on the analysis of marathon vs. ultramarathon performances of men and women. We reasoned that the best comparison of the potential of a human is by the use of world best times, which should be reasonable indicators of the effect of distance on relative performance of women and men. We compared current world best running performances at distances from 100 m to 200 km. Records as of December 2002 were obtained. T-tests analyzed speed differences between genders, and regression analysis tested the percent differences between men and women across distance. Speeds were different, with the average difference being 12.4% faster for men. There was a significant slope to the speed difference across distances in that longer distances were associated with greater differences. These results may be confounded by the reduced number of women in longer distance events. Furthermore, the proposed metabolic advantage for women because of increased fat metabolism may be masked by regular feeding during endurance races.

Effect of ammonia on in vitro diaphragmatic contractility, fatigue and recovery.

BACKGROUND: Following strenuous exercise, in vivo diaphragmatic strength has been reported to decrease. This decrease has been suggested to result from an increase in metabolic by-products of intense exercise. OBJECTIVE: We tested the hypothesis that physiological NH(3) concentrations adversely affect diaphragmatic contractility, fatigability, and recovery. METHODS: Rat diaphragm strips were exposed to one of six experimental conditions (n = 6 per condition): Krebs-Ringer control solution, or the control solution with NH(3) added (in mM): 0.11, 2.5, 5.0, 10.0, or 14.0. Initial diaphragmatic contractility was assessed with the force-frequency response in the control solution. Following the first force-frequency response, the solution was replaced with one of the six solutions and a second force-frequency response was measured. Strips were then subjected to a short fatigue protocol and contractility was reassessed with a third force-frequency response. A longer fatigue protocol was then administered, followed by a 20-min recovery assessment period. RESULTS: Ammonia significantly (p < 0.05) reduced diaphragmatic contractility, but only at concentrations of 5 mM or greater. Additionally, ammonia did not alter the rate of fatigue. CONCLUSIONS: This study suggests that physiological NH(3) concentrations do not adversely affect in vitro diaphragmatic contractility, fatigue, or recovery. These data are not consistent with diaphragmatic fatigue associated with exercise induced by arterial concentrations of NH(3) seen in humans, although further testing in situ or in vivo is needed.

Effect of recovery interval on multiple-bout sprint cycling performance after acute creatine supplementation.

The purpose of this study was to examine the effect of varying recovery intervals on multiple-bout, short-duration, high-intensity cycling efforts of adult men supplemented with creatine (Cr) or a placebo (Pl). Thirty subjects underwent 3 trials of a maximal cycling protocol (T(0), T(1), T(2)). T(0) included V(O)2 max testing and familiarization with the sprint cycling protocol. T(1) consisted of 8 15-second bouts of sprint cycling exercise. Subjects were randomly assigned to recovery interval groups (1 minute, 3 minutes, 6 minutes), and Cr or Pl groups (0.3 g x kg(-1) x d(-1)). Posttesting (T(2)) took place 7 days after T(1) and consisted of an identical protocol as during T(1). Changes in mean power (MP), peak power (PP), and fatigue index (FI) were compared between trials. MP was significantly increased in Cr 1-minute, Cr 3-minute, and Pl 6-minute groups (p < 0.05). Significant PP increases were demonstrated in Cr 1-minute and Pl 6-minute groups (p < 0.05), and FI significantly increased in Pl 1-minute group (p < 0.05). Results indicate that Cr supplementation is effective in improving recovery from repeated sprint cycling performances when the recovery interval is of a short (<6 minutes) duration.