Carbon dioxide alters the Hoffmann reflex independent of hydrogen ions.

The purpose of this study was to examine the effect of changes in capillary blood pH on the resting soleus Hoffmann (H) reflex in the intact human. H-max size, H-wave at 20% of H-max, M-max and H-reflex latency were recorded in 10 subjects (apparently healthy, ages 19-36) before and after exposure to 3 hours of NaHCO(3), CaCO(3), NH(4)Cl (all at 0.3 g/kg) or 10 minutes 7% Carbon dioxide (CO(2)) administration. NaHCO(3) increased capillary blood pH, CaCO(3) did not change capillary blood pH, and NH(4)Cl and 7% CO(2) decreased capillary blood pH. H-max and H-wave at 20% of M-max size were significantly decreased with no change in M-max, and H-reflex latency significantly increased during 7% CO(2) administration only. No other changes in H-maximum size or H-reflex latency in response to dry chemical administration were observed. Seven percent CO(2) administration reduces the size and increases the latency of the H-maximum size as previously found, but other chemicals which alter capillary blood pH do not. CO(2) modulates afferent nerve function, and does so, it appears, independent of changes in capillary blood pH.

A neuromuscular intervention for exercise-related medial leg pain.

CONTEXT: Exercise-related medial leg pain (ERMLP) is a common complaint among athletes, and efforts toward rehabilitation are often unsuccessful. OBJECTIVE: To evaluate the efficacy of a therapeutic intervention in ERMLP localized to soft tissue. DESIGN: A quasi-experimental, nonequivalent control-group study. SETTING: Athletic training facility. PATIENTS: 20 volunteer male and female athletes (18-22 y old) with ERMLP. Complete data were available for 13 participants. INTERVENTION: Treatment group (TRE, n = 7) received therapeutic intervention focused on relieving muscle hypertonicity in the deep compartment of the lower leg and restoring balance of the toe flexors and extensors. Control group (CON, n = 6) received no intervention. MAIN OUTCOME MEASURES: Self-reported pain intensity, pain threshold, and extensor hallucis longus to extensor digitorum brevis (EHL:EDB) electromyography ratio. RESULTS: There were no significant differences in age, duration of symptoms, or pain measures between the 2 groups at baseline. CON demonstrated no significant changes in any of the outcome measures in posttreatment testing, but significant between-groups differences were identified for pain during activity (CON mean = 6.5, 95% CI 5.05, 7.95; TRE mean = 3.5, 95% CI 1.67, 5.33; P = .01), change scores for pain during activity (CON mean = 0.33, 95% CI -1.25, 1.91; TRE mean = -3.43, 95% CI:-4.6, -2.25; P < .001), change scores in pressure threshold (CON mean = -0.25, 95% CI -0.74, 0.23; TRE mean = 0.72, 95% CI 0.22, 1.37; P = .006), and change in EHL:EDB ratios (CON mean = 0.05, 95% CI -0.22, 0.33; TRE mean = 1.07, 95% CI 0.75, 2.07; P < .046). CONCLUSION: Therapeutic interventions focused on restoring muscle balance appear to be effective in resolving ERMLP.

Increase in maximal oxygen uptake following 2-week walk training with blood flow occlusion in athletes.

Walk training with blood flow occlusion (OCC-walk) leads to muscle hypertrophy; however, cardiorespiratory endurance in response to OCC-walk is unknown. Ischemia enhances the adaptation to endurance training such as increased maximal oxygen uptake (VO2(max)) and muscle glycogen content. Thus, we investigated the effects of an OCC-walk on cardiorespiratory endurance, anaerobic power, and muscle strength in elite athletes. College basketball players participated in walk training with (n = 7) and without (n = 5) blood flow occlusion. Five sets of a 3-min walk (4-6 km/h at 5% grade) and a 1-min rest between the walks were performed twice a day, 6 days a week for 2 weeks. Two-way ANOVA with repeated measures (groups x time) was utilized (P < 0.05). Interactions were found in VO2(max) (P = 0.011) and maximal minute ventilation (VE(max); P = 0.019). VO2(max) (11.6%) and VE(max) (10.6%) were increased following the OCC-walk. For the cardiovascular adaptations of the OCC-walk, hemodynamic parameters such as stroke volume (SV) and heart rate (HR) at rest and during OCC-walk were compared between the first and the last OCC-walk sessions. Although no change in hemodynamics was found at rest, during the last OCC-walk session SV was increased in all five sets (21.4%) and HR was decreased in the third (12.3%) and fifth (15.0%) sets. With anaerobic power an interaction was found in anaerobic capacity (P = 0.038) but not in peak power. Anaerobic capacity (2.5%) was increased following the OCC-walk. No interaction was found in muscle strength. In conclusion, the 2-week OCC-walk significantly increases VO2(max) and VE(max) in athletes. The OCC-walk training might be used in the rehabilitation for athletes who intend to maintain or improve endurance.

Incidence, prevalence, and risk of eating disorder behaviors in military academy cadets.

Eating disorders are a particular problem for college students, as well as college athletes and military personnel. We examined the incidence, prevalence, and risk of eating disorders at the United States Military Academy (USMA) over a 7-year period (total population 12,731 cadets). The incidence per year for females was 0.02% for anorexia, 0.17% for bulimia, and 0.17% for eating disorders not otherwise specified (EDNOS) and for males was 0.0% for anorexia, 0.003% for bulimia, and 0.02% for eating disorders not otherwise specified. The total prevalence of diagnosed eating disorders for females was 5% and for males was 0.1%. For females over the 7-year period, we found a prevalence of 0.2% for anorexia, 1.2% for bulimia, 1.2% for eating disorders not otherwise specified, and for males we found a prevalence of 0.0% for anorexia, 0.02% for bulimia, and 0.03% for eating disorders not otherwise specified. Nineteen percent of females and 2% of males scored a 20 or higher on the Eating Attitudes Test (EAT)-26 survey indicating they were at risk for developing an eating disorder. We conclude that the prevalence of eating disorders at USMA is comparable to civilian colleges.

High REE in Sumo wrestlers attributed to large organ-tissue mass.

PURPOSE: It is unknown whether high resting energy expenditure (REE) in athletes is attributable to changes in organ-tissue mass and/or metabolic rate. The purpose of this study was to examine the contribution of organ-tissue mass of fat-free mass (FFM) components to REE for Sumo wrestlers who have large FFM and REE. We investigated the relationship between the REE measured by indirect calorimetry and the REE calculated from organ-tissue mass using a previously published approach. METHODS: Ten Sumo wrestlers and 11 male untrained college students (controls) were recruited to participate in this study. FFM was estimated by two-component densitometry. Contiguous magnetic resonance imaging (MRI) images with a 1-cm slice thickness were obtained from the top of head to the ankle joints, and the cross-sectional area and volume were determined for skeletal muscle (SM), liver, kidney, and brain. The volume of adipose tissue, heart, and residual was calculated from each equation. The volume units were converted into mass by an assumed constant density. The measured REE was determined by indirect calorimetry. The calculated REE was estimated as the sum of individual organ-tissue masses (seven body compartments) multiplied by their metabolic rate constants. RESULTS: The measured REE for Sumo wrestlers (2286 kcal x d(-1)) was higher (P<0.01) than for controls (1545 kcal x d(-1)). Sumo wrestlers had a greater amount of FFM and FFM components (e.g., SM, liver, and kidney), except for brain. The ratio of measured REE to FFM and the measured REE adjusted by FFM were similar between the two groups. The measured REE values for Sumo wrestlers were not significantly different from the calculated REE values. CONCLUSIONS: The high REE for Sumo wrestlers can be attributed not to an elevation of the organ-tissue metabolic rate, but to a larger absolute amount of low and high metabolically active tissue including SM, liver, and kidney.

Effects of heavy load carriage during constant-speed, simulated, road marching.

Load carriage is a key element in dismounted military operations. Load carriage requirements in the field regularly exceed 50% of lean body mass (LBM) and have only rarely been studied. Therefore, our purpose was to determine the metabolic and motivational effects of heavy loads (30-70% LBM) during constant-rate "road" marching on a treadmill. Ten healthy male Army officers carried loads of 30%, 50%, and 70% LBM in an all-purpose, lightweight, individual, carrying equipment pack for 30 minutes, at a speed of 6 km/h. Oxygen consumption (VO2), ventilation, heart rate (HR), respiratory exchange ratio, rating of perceived exertion (RPE), and Self-Motivation Inventory scores were recorded at each trial. Significant increases were observed for VO2, ventilation, and HR between the trials. RPE significantly increased for the 70% LBM trial, compared with the 30% and 50% trials. No significant differences were seen in respiratory exchange ratio or Self-Motivation Inventory scores. Increasingly heavy loads carried in a rucksack resulted in increased VO2, RPE, and HR; therefore, increasing the load that a soldier is required to carry may negatively affect road march performance.

Metabolic effects of soldier performance on a simulated graded road march while wearing two functionally equivalent military ensembles.

OBJECTIVES: The purpose of this study was to examine metabolic effects of soldier performance on a simulated road march, comparing two functionally equivalent military ensembles (FEMEs) with changing gradation of marching, and to create prediction equations addressing workload with different loads and treadmill grades. METHODS: Fourteen male military subjects were tested while wearing two different FEMEs on a graded (0%, 5%, or 10%), 3.5 miles/h, road march for 30 minutes. Data collected included oxygen uptake (VO2), carbon dioxide output, ventilation, respiratory exchange ratio, and heart rate (HR). RESULTS: No significant differences were found between the two FEMEs in each graded condition. Combining ensemble data, significant differences occurred in all conditions, comparing all grades. A 10% graded road march (3.5 miles/h, approximately 27-kg load) represented 61% to 90% of maximal values. For treadmill grades of <10%, VO2 and HR were modeled as follows (adjusted R2 = 0.89 [VO2] and 0.82 [HR]): VO2 (mL/kg per minute) = 10 + [2 - grade (%)] + [0.2 - load (% of body mass)]; HR (beats per minute) = 90 + [6 . grade (%)] + [0.7 - load (% of body mass)]. CONCLUSIONS: Three factors, namely, elevation grade, equipment weight (load), and overall subject physical abilities, were significant for overall metabolic demand during a simulated graded road march and might affect field performance.

Comparison of normalized maximum aerobic capacity and body composition of sumo wrestlers to athletes in combat and other sports.

Sumo wrestling is unique in combat sport, and in all of sport. We examined the maximum aerobic capacity and body composition of sumo wrestlers and compared them to untrained controls. We also compared "aerobic muscle quality", meaning VO2max normalized to predicted skeletal muscle mass (SMM) (VO2max /SMM), between sumo wrestlers and controls and among previously published data for male athletes from combat, aerobic, and power sports. Sumo wrestlers, compared to untrained controls, had greater (p < 0.05) body mass (mean ± SD; 117.0 ± 4.9 vs. 56.1 ± 9.8 kg), percent fat (24.0 ± 1.4 vs. 13.3 ± 4.5), fat-free mass (88.9 ± 4.2 vs. 48.4 ± 6.8 kg), predicted SMM (48.2 ± 2.9 vs. 20.6 ± 4.7 kg) and absolute VO2max (3.6 ± 1.3 vs. 2.5 ± 0.7 L·min(-1)). Mean VO2max /SMM (ml·kg SMM(-1)·min(-1)) was significantly different (p < 0.05) among aerobic athletes (164.8 ± 18.3), combat athletes (which was not different from untrained controls; 131.4 ± 9.3 and 128.6 ± 13.6, respectively), power athletes (96.5 ± 5.3), and sumo wrestlers (71.4 ± 5.3). There was a strong negative correlation (r = - 0.75) between percent body fat and VO2max /SMM (p < 0.05). We conclude that sumo wrestlers have some of the largest percent body fat and fat-free mass and the lowest "aerobic muscle quality "(VO2max /SMM), both in combat sport and compared to aerobic and power sport athletes. Additionally, it appears from analysis of the relationship between SMM and absolute VO2max for all sports that there is a "ceiling "at which increases in SMM do not result in additional increases in absolute VO2max. Key PointsSumo wrestlers have a high absolute VO2max compared to untrained controls.However, sumo wrestlers have a low VO2max /kg of skeletal muscle mass compared to other combat sports, other strength/power sports, and untrained controls.The reason for this is unknown, but is probably related to alterations in sumo skeletal muscle compared to other sports.Based on the present and previous data, there appears to be a "ceiling "at which increases in skeletal muscle mass do not result in additional increases in absolute VO2max.

Myosin heavy chain profiles and body composition are different in old versus young Standardbred mares.

There are limited data on age-related changes in body composition or skeletal muscle in the horse. Therefore, the purpose of this study was to investigate any differences in muscle myosin heavy chain (MHC) and body composition associated with aging. Twenty-three young (4-8 years) and eight old (20+ years) unfit Standardbred mares were evaluated. Rump fat thickness was measured using B-mode ultrasound and per cent body fat (% fat) was calculated. Needle muscle biopsies were obtained from right gluteus medius muscle. MHC composition was determined via sodium dodecyl sulphate-polyacrylamide gel electrophoresis. Three MHC isoforms were subsequently identified as type I, type IIA, and type IIX and quantified using a scanning and densometric system. There were no significant differences (p>0.05) between old and young mares in fat (%) (19.0+/-6.4 vs 20.5+/-5.4), fat mass (kg) (102.3+/-39.9 vs 106.9+/-37.1), or body weight (kg) (529.4+/-34.9 vs 512.7+/-57.7). However, the old mares had significantly (p<0.05) greater lean body mass than the young mares (427.1+/-24.5 vs 405.7+/-37.9). Aged mares had significantly (p<0.05) less type I (7.8+/-2.9% vs 12.1+/-4.4%) and IIA (27.8+/-7.1% vs 36.1+/-9.5%) fibres than the young group but more type IIX (64.6+/-4.7% vs 51.8+/-11.1%). The MHC data are consistent with the age-related changes seen in other species.

Modified Kaatsu training: adaptations and subject perceptions.

PURPOSE: Although Kaatsu training involves low training loads, high perceived exertion and pain scores suggest that potential benefits may be offset by poor adherence or tolerance, particularly if applied in untrained or clinical populations. The purpose of this study was to investigate muscle adaptations, perceived exertion ratings, perceived sensations, and exercise adherence to a modified Kaatsu training protocol involving upper arm exercise. METHODS: Forty subjects ages 18-30 yr were assigned to exercise (EX) or nonexercise control (CON) groups. The EX group performed three sets of 15 repetitions of unilateral biceps and triceps exercises, three times per week for 8 wk while wearing a pneumatic cuff to restrict blood flow on one arm (CUFF) and nothing on the other (NCUFF). The CON group did not exercise but wore the cuff on one arm for a comparable amount of time. Strength, girth, tomography scans along with RPE, and sensations during workouts were assessed. Perceived exertion and sensations were assessed during workouts using visual analog scales. RESULTS: Biceps curl and triceps extension strength along with arm size increased during the 8-wk period when compared with the CON group. Compliance was 85.4% and 97% for the EX and CON groups, respectively. EX subjects completed 85.4% of their workouts, whereas controls attended 90.4% of their sessions. The prominent sensations reported in the CUFF arm were pressure and aching. CONCLUSIONS: The Kaatsu training used in this study yielded moderate exertion ratings and low-pressure sensations, increased muscle size and strength, and was well tolerated, thereby lending support to Kaatsu training's potential as a training modality for untrained or clinical populations.

Effect of breathing 7% carbon dioxide on the human soleus Hoffmann-reflex recruitment curve.

OBJECTIVE: To examine the effect of inhaling 7% carbon dioxide on the recruitment curve of the soleus H-reflex. METHODS: Five males and five females (apparently healthy; 21-40 yr) with surface EMG electrodes over the soleus muscle randomly breathed room air or a 7% CO2, 21% O2, balance N2 mix for 10 min. The tibial nerve was stimulated to elicit the H-reflex recruitment curve. H-reflex threshold, motor threshold, slope of ascending H-reflex curve, Hmax:Mmax ratio, and latency of Hmax were compared. RESULTS: Breathing 7% carbon dioxide increased the H-reflex threshold (as a percent of motor threshold) from 73% (SD 0.09) to 84% (SD 0.12; p<0.05), decreased the Hmax:Mmax ratio from 0.504 (SD 0.290) to 0.403 (SD 0.253; p<0.05), and increased the H wave latency (in msec) from 32.8 (SD 1.6) to 34.6 (SD 2.6; p<0.05). Slope of ascending H-reflex curve (room air: 125 (SD 89); CO2: 135 (SD 92); p>0.05), Mmax (room air: 3.70 mV (SD 1.57); CO2: 3.69 mV (SD 1.53); p>0.05), and motor threshold (p>0.05) remained unchanged. CONCLUSIONS: Breathing 7% carbon dioxide reduces afferent synaptic transmission in the soleus muscle by slowing transmission, increasing threshold stimulus, and reducing H wave size. SIGNIFICANCE: Clinicians and scientists should consider the possibility that carbon dioxide can reduce afferent synaptic transmission.

Contractile properties of skeletal muscle fibre bundles from mice deficient in carbonic anhydrase II.

The function of cytosolic carbonic anhydrase (CA) isozyme II is largely unknown in skeletal muscle. Because of this, we compared the in vitro contractile properties of extensor digitorum longus (EDL) and soleus (SOL) fibre bundles from mice deficient in CA II (CAD) to litter mate controls (LM). Twitch rise, 1/2 relaxation time and peak twitch force at 22 degrees C of fibre bundles from CAD EDL [28.4+/-1.4 ms, 31.2+/-2.3 ms, 6.2+/-1.0 Newton/cm(2) (N/cm(2)), respectively] and CAD SOL (54.2+/-7.5 ms, 75.7+/-13.8 ms, 2.9+/-0.5 N/cm(2), respectively) were significantly higher compared to LM EDL (20.5+/-2.2 ms, 21.9+/-3.7 ms, 4.5+/-0.2 N/cm(2)) and LM SOL (42.8+/-3.5 ms, 51.4+/-2.4 ms, 2.1+/-0.4 N/cm(2)). However, in acidic Krebs-Henseleit solution, mimicking the pH, PCO(2), and HCO(3) (-) of arterial blood from CAD mice, twitch rise, 1/2 relaxation time, and peak twitch force of fibre bundles from CAD EDL (19.3+/-0.7 ms, 19.7+/-2.3 ms, 4.8+/-0.8 N/cm(2)) and CAD SOL (41.4+/-3.6 ms, 51.9+/-5.5 ms, 2.2+/-0.7 N/cm(2)) were not significantly different from LM fibre bundles in normal Krebs-Henseleit solution (EDL: 19.7+/-1.1 ms, 21.6+/-0.6 ms, 4.7+/-0.2 N/cm(2); SOL: 42.5+/-3.1 ms, 51.8+/-2.6 ms, 1.8+/-0.3 N/cm(2)). A higher pH(i) during exposure to acidic bathing solution was maintained by CAD EDL (7.37+/-0.02) and CAD SOL (7.33+/-0.05) compared to LM EDL (7.28+/-0.04) and LM SOL (7.22+/-0.02). This suggests that the skeletal muscle of CAD mice possesses an improved defense of pH(i) against elevated pCO(2). In support of this, apparent non-bicarbonate buffer capacity (in mequiv H(+) (pH unit)(-1) (kg cell H(2)O)(-1)) as determined by pH microelectrode was markedly increased in CAD EDL (75.7+/-4.1) and CAD SOL (85.9+/-3.3) compared to LM EDL (39.3+/-4.7) and LM SOL (37.5+/-3.8). Both latter phenomena may be related to the slowed rate of intracellular acidification seen in CAD SOL in comparison with LM SOL upon an increase in PCO(2) of the bath. In conclusion, skeletal muscle from mice deficient in CA II exhibits altered handling of acid-base challenges and shows normal contractile behavior at normal intracellular pH.

Depression of h-reflex following carbonic anhydrase inhibition appears unrelated to changes in synaptic effectiveness.

Presynaptic inhibition (PI) of Ia afferents was examined as a possible contributor to the depression of the soleus H-reflex following carbonic anhydrase (CA) inhibition with Acetazolamide (ACZ). Ten males (aged 22-32) were studied in two randomized conditions, control and ACZ administration (250 mg 14, 8, and 2 h before testing) separated by at least one week. PI of soleus Ia afferents was indirectly assessed two ways: a conditioning stimulus of Ia afferents in the common peroneal nerve (N = 6), and heteronymous Ia facilitation from the quadriceps to soleus muscle (N = 4). Conditioning (C) of the soleus H-reflex (common peroneal nerve stimulation protocol) resulted in depression of the H-reflex in the supine and standing position compared to the test (T, unconditioned) H-reflex in the same position. This result was unaltered following ACZ treatment. C (heteronymous facilitation protocol) resulted in facilitation of the H-reflex in the supine, but not the standing position. This result was unaltered following ACZ treatment. It was concluded that the depression of the H-reflex following CA inhibition (present study; Brechue et al., 1997) appears to be unrelated to changes in the tonic level of PI of Ia afferents. The best hypothesis for the reduction in the H-reflex appears to be conduction block of the primary afferent fibers secondary to local increases in PCO2.

Hypercapnic impairment of neuromuscular function is related to afferent depression.

Acetazolamide (ACZ), a carbonic anhydrase inhibitor, results in altered neuromuscular function secondary to depressed afferent transmission in intact humans. One effect of ACZ is hypercapnia. Thus, to test if the neuromuscular depression observed following ACZ treatment is related to elevated CO(2), human subjects ( n=10) were exposed to 15 min of room air (0% CO(2)) or hypercapnia (7% inspired CO(2)), and neuromuscular function was evaluated. Isometric force (36.8 to 31.1 N) and peak-to-peak electromyographic amplitude (EMG, 1.5 to 1.0 mV) associated with an Achilles tendon tap, and soleus H(max):M(max) ratio (69.0 to 62.2%) were depressed, while EMG latency (34.8 to 39.8 ms) was increased by hypercapnia. Reflex recovery profiles (following a conditioning tap to the contralateral Achilles tendon), motor nerve conduction velocity, amplitude of the maximum M-wave, and peak twitch tension at M(max) were unaltered by hypercapnia. We conclude that elevated CO(2) impairs neuromuscular function through effects on afferent transmission or synaptic integrity between type Ia fibers of the muscle spindle and the alpha motor neuron, without affecting the muscle spindle, efferent conduction or skeletal muscle force-generating capacity.