Biomedical subjects

K W Rundell

Publications and source records attributed to K W Rundell.

At least 19 recordsLinked to original sources

PubMed2005

Dietary polyunsaturated fatty acids in asthma- and exercise-induced bronchoconstriction.

Despite progress that has been made in the treatment of asthma, the prevalence and burden of this disease has continued to increase. While pharmacological treatment of asthma is usually highly effective, medications may have significant side effects or exhibit tachyphylaxis. Alternative therapies for treatment that reduce the dose requirements of pharmacological interventions would be beneficial, and could potentially reduce the public health burden of this disease. Ecological and temporal data suggest that dietary factors may have a role in recent increases in the prevalence of asthma. A possible contributing factor to the increased incidence of asthma in Western societies may be the consumption of a proinflammatory diet. In the typical Western diet, 20- to 25-fold more omega (n)-6 polyunsaturated fatty acids (PUFA) than n-3 PUFA are consumed, which promotes the release of proinflammatory arachidonic acid metabolites (leukotrienes and prostanoids). This review will analyze the evidence for the health effects of n-3 PUFA in asthma- and exercise-induced bronchoconstriction (EIB). While clinical data evaluating the effect of omega-3 fatty acid supplementation in asthma has been equivocal, it has recently been shown that fish oil supplementation, rich in n-3 PUFA, reduces airway narrowing, medication use, and proinflammatory mediator generation in nonatopic elite athletes with EIB. These findings are provocative and suggest that dietary fish oil supplementation may be a viable treatment modality and/or adjunct therapy in asthma and EIB.

Airway Resistance↗

PubMed2005

Effects of montelukast on airway narrowing from eucapnic voluntary hyperventilation and cold air exercise.

BACKGROUND: Exercise induced bronchoconstriction (EIB) is common in elite athletes. Eucapnic voluntary hyperventilation (EVH) is a laboratory test recommended for the identification of EIB in athletes, secondary to a field exercise challenge. Montelukast attenuates EIB, but its protective effect against airway narrowing from EVH has not been investigated. OBJECTIVE: To examine the effectiveness of montelukast after exercise and after EVH. METHODS: A randomised, placebo controlled, double blind, crossover study was performed with 11 physically active EIB positive subjects (eight men, three women; mean (SD) age 22.8 (6.8) years). Six hours before each of the following challenges 10 mg montelukast or placebo was ingested: (a) a six minute, cold air (-3 degrees C) maximal effort work accumulation cycle ergometer exercise; (b) EVH, breathing 5% CO(2) compressed air at 85% maximal voluntary ventilation for six minutes. Spirometry was performed before and 5, 10, and 15 minutes after the challenge. At least 48 hours was observed between challenges. RESULTS: No differences in forced expiratory volume in one second (FEV(1)) were found after the two challenges. Exercise and EVH resulted in falls in FEV(1) of 22.4 (18.0) and 25.6 (16.8) respectively. Falls in FEV(1) after montelukast were less than after placebo (10.6 (10.6) and 14.3 (11.3) after exercise and EVH respectively; p<0.05). Montelukast provided protection against bronchoconstriction (59% and 53%; p<0.05) for eight exercising subjects and 10 EVH subjects; no protection was afforded for three exercising and one EVH challenged subject. CONCLUSIONS: Both exercise and EVH were potent stimuli of airway narrowing. A single dose of montelukast provided reasonable protection in attenuating bronchoconstriction from either exercise or EVH. The similar protection by montelukast suggests that EVH is a suitable laboratory surrogate for EIB evaluation.

Acetates↗

PubMed2001

Muscle oxygen desaturation is related to whole body VO2 during cross-country ski skating.

Previous research has demonstrated that blood flow and subsequent O2 desaturation (OD) in exercising muscle is related to the static component during exercise. In speed skating, increased OD is dissociated from whole body VO2 and heart rate (HR) when the skater increases the static component by 'sitting low'. This phenomenon was evaluated in cross-country skiers by manipulating speed and incline during treadmill roller skiing. Eight male cross-country skiers (22.4 +/- 3.2 yrs old) randomly performed constant incline- and constant speed-based protocols in which increased load was manipulated in five 4min stages by treadmill incline or speed change, respectively. A strong relationship (r = 0.83) was observed between VO2 and % OD while blood volume change (deltaBV) was minimal. Unexpectedly, no HR/ VO2 or HR/OD shifts were observed between protocols. The % OD response, in relation to blood lactate values, during submaximal exercise was very similar to that of VO2. The lack of an observed greater desaturation at higher inclines suggests that the expected static load may be attenuated by an increased contribution of poling. The strong relationship of % OD to whole body VO2 may be attributed to O2 dissociation in the capillary bed of the muscle to meet aerobic energy demand and is independent of blood flow dynamics during cross-country ski skating.

Adult↗

PubMed2001

Self-reported symptoms and exercise-induced asthma in the elite athlete.

PURPOSE: The purpose of this study was to compare self-reported symptoms for exercise-induced asthma (EIA) to postexercise challenge pulmonary function test results in elite athletes. METHODS: Elite athletes (N = 158; 83 men and 75 women; age: 22 +/- 4.4 yr) performed pre- and post-exercise spirometry and were grouped according to postexercise pulmonary function decrements (PFT-positive, PFT-borderline, and PFT-normal for EIA). Before the sport/environment specific exercise challenge, subjects completed an EIA symptoms-specific questionnaire. RESULTS: Resting FEV1 values were above predicted values (114--121%) and not different between groups. Twenty-six percent of the study population demonstrated >10% postexercise drop in FEV1 and 29% reported two or more symptoms. However, the proportion of PFT-positive and PFT-normal athletes reporting two or more symptoms was not different (39% vs. 41%). Postrace cough was the most reported symptom, reported significantly more frequently for PFT-positive athletes (P < 0.05). Sensitivity/specificity analysis demonstrated a lack of effectiveness of self-reported symptoms to identify PFT-positive or exclude PFT-normal athletes. Postexercise lower limit reference ranges (MN-2SDs) were determined from normal athletes for FEV1, FEF25--75% and PEF to be -7%, -12.5%, and -18%, respectively. CONCLUSION: Although questionnaires provide reasonable estimates of EIA prevalence among elite cold-weather athletes, the use of self-reported symptoms for EIA diagnosis in this population will likely yield high frequencies of both false positive and false negative results. Diagnosis should include spirometry using an exercise/environment specific challenge in combination with the athlete's history of asthma symptoms.

Adolescent↗

PubMed2001

Hemoglobin/myoglobin oxygen desaturation during Alpine skiing.

PURPOSE: To investigate muscle blood volume (BV) change and hemoglobin/myoglobin oxygen desaturation (OD) during simulated giant slalom (GS) and slalom (SL) Alpine ski racing. METHODS: Joint angle, BV, OD, and heart rate (HR) were evaluated during GS and SL events in 30 junior elite skiers ages 9--17 yr (13.5 +/- 2.3). Subjects were stratified by ski class and age: group I, J1 and J2, ages 15--18 yr (16.8 +/- 0.8); group II, J3, 13--14 yr (13.6 +/- 0.7); and group III, J4 and J5, 9--12 yr (11.5 +/- 1.2). Near-infrared spectrophotometry (NIRS) was used to measure BV and OD in the capillary bed of the vastus lateralis during trials. Maximal OD was determined during thigh cuff ischemia (CI). Quadriceps cross-sectional area (CSA) was estimated by skin-fold and thigh circumference. RESULTS: Joint angles were smaller (P < 0.05) during GS than SL for ankle (83.8 +/- 11.9 degrees; 98.6 +/- 15.7 degrees ), knee (107.4 +/- 14.9 degrees; 118.3 +/- 18.0 degrees ), and hip (98.8 +/- 14.3 degrees; 107.5 +/- 16.2 degrees ). BV reduction from rest to peak exercise (Delta BV) was 30% greater (P < 0.05) during the GS than SL, whereas Delta OD was 33% greater (P < 0.05) during GS. Delta OD, relative to CI OD, was greater for all subjects during GS (79.2 +/- 3.7%) than SL (65.7 +/- 4.4%). This pattern continued within groups; group II displayed the greatest relative desaturation (82.9 +/- 7.6%). CSA was larger in older skiers (92.5 +/- 21.6; 72.5 +/- 12.3; 65.3 +/- 21.2 cm(2)) and correlated with Delta OD (P < 0.05). CONCLUSION: The larger reduction in BV (Delta BV change) and greater OD when skiers assumed lower posture during GS than SL may be related to greater effective static load secondary to higher percent of maximal voluntary contraction and is consistent with compromised blood flow to working muscle.

Adolescent↗

PubMed2000

Exercise-induced asthma screening of elite athletes: field versus laboratory exercise challenge.

PURPOSE: The purpose of this study was to compare a laboratory based exercise challenge (LBC) to a field based exercise challenge (FBC) for pulmonary function test (PFT) exercise-induced asthma (EIA) screening of elite athletes. METHODS: Twenty-three elite cold weather athletes (14 men, 9 women) PFT positive for EIA (FBC screened) served as subjects. Twenty-three gender and sport matched controls (nonasthmatics) were randomly selected to establish PFT reference values for normal elite athletes. Before FBC, athletes completed a medical history questionnaire for EIA symptoms. FBC evaluations consisted of baseline spirometry, actual or simulated competition, and 5, 10, and 15 min postexercise spirometry. PFT positive athletes were evaluated in the laboratory using an exercise challenge simulating race intensity (ambient conditions: 21 degrees C, 60% relative humidity). PFT procedures were identical to FBC. RESULTS: 91% of PFT positive and 48% of PFT normal athletes reported at least one symptom of EIA, with postrace cough most frequent. Baseline spirometry was the same for PFT positives and normal controls. Lower limit reference range (MN - 2 SD) of FEV1 for controls suggests that postexercise decrements of greater than approximately -7% indicate abnormal airway response in this population. Exercise time duration did not effect bronchial reactivity; 78% of FBC PFT positives were PFT normal post-LBC. CONCLUSION: Self-reported symptoms by elite athletes are not reliable in identifying EIA. Reference range criterion for FEV1 decrement in the elite athlete postexercise contrasts current recommended guidelines. Moreover, a large number of false negatives may occur in this population if EIA screening is performed with inadequate exercise and environmental stress.

Adolescent↗

PubMed2000

Incidence of exercise-induced bronchospasm in Olympic winter sport athletes.

PURPOSE: The purpose of this project was to determine the incidence of exercise-induced bronchospasm (EIB) among U.S. Olympic winter sport athletes. METHODS: Subjects included female and male members of the 1998 U.S. Winter Olympic Team from the following sports: biathlon, cross-country ski, figure skating, ice hockey, Nordic combined, long-track speedskating, and short-track speedskating. Assessment of EIB was conducted in conjunction with an "actual competition" (Olympic Trials, World Team Trials, World Cup Event, U.S. National Championships) or a "simulated competition" (time trial, game), which served as the exercise challenge. Standard spirometry tests were performed preexercise and at 5, 10, and 15 min postexercise. An athlete was considered EIB-positive based on a postexercise decrement in FEV1 > or = 10%. RESULTS: For the seven sports evaluated on the 1998 U.S. Winter Olympic Team, the overall incidence of EIB across all sports and genders was 23%. The highest incidence of EIB was found in cross-country skiers, where 50% of the athletes (female = 57%; male = 43%) were diagnosed with EIB. Across the seven sports evaluated, the prevalence of EIB among the female and male athletes was 26% and 18%, respectively. Among those individuals found to be EIB-positive were athletes who won a team gold medal, one individual silver medal, and one individual bronze medal at the Nagano Winter Olympics. CONCLUSIONS: These data suggest that: 1) EIB is prevalent in several Olympic winter sports and affects nearly one of every four elite winter sport athletes; 2) the winter sport with the highest incidence of EIB is cross-country skiing; 3) in general, EIB is more prevalent in female versus male elite winter sport athletes; and 4) athletes may compete successfully at the international level despite having EIB.

Asthma, Exercise-Induced↗

PubMed1999

Upper body power comparison between groups of cross-country skiers and runners.

The purpose of this study was to evaluate relationships between upper body power (UBP) and cross-country ski skating race velocity (R) in a cross sectional representation of cross-country skiers. Additionally, cross-country skiers' UBP was compared to UBP of distance runners. Participants (n = 195) were tested on a Street Arm Ergometer for UBP using a ramped maximal UBP test simulating a double poling motion. A strong relationship (r = 0.89) between UBP and RV in skiers was determined. High school skiers were separated into slow and fast groups based on reported RV; significant differences (p < 0.05) in both UBP was found to be an effective partial predictor of RV, independent of gender. Mean UBP for the cross-country runners was 46% of mean UBP for the cross-country skiers. With UBP contributing so much to performance in cross-country ski racing, it is recommended that cross-country skiers focus a large portion of their training on the specific development of that fitness component.

Adolescent↗

PubMed1999

Evidence for restricted muscle blood flow during speed skating.

INTRODUCTION: We have previously hypothesized restricted muscle blood flow during speed skating, secondary to the high intramuscular forces intrinsic to the unique posture assumed by speed skaters and to the prolonged duty cycle of the skating stroke. METHODS: To test this hypothesis, we studied speed skaters (N = 10) during submaximal and maximal cycling and in-line skating, in both low (knee angle = 107 degrees) and high (knee angle = 112 degrees) skating positions (CE vs SkL vs SkH). Supportive experiments evaluated muscle desaturation and lactate accumulation during on-ice speed skating and muscle desaturation during static exercise at different joint positions. RESULTS: Consistent with the hypothesis were reductions during skating in VO2peak (4.28 vs 3.83 vs 4.26 L x min(-1)), the VO2 at 4 mmol x L(-1) blood lactate (3.38 vs 1.93 vs 3.31 L x min(-1)), and cardiac output during maximal exercise (33.2 vs 25.3 vs 25.6 L x min(-1)). The reduction in maximal cardiac output was not attributable to differences in HRmax (197 vs 192 vs 193 b x min(-1)) but to a reduction in SVmax (172 vs 135 vs 134 mL x beat(-1)). The reduction in SV appeared to be related to an increased calculated systemic vascular resistance (354 vs 483 vs 453 dynes x s(-1) x cm(-1)). During maximal skating there was also a greater % O2 desaturation of the vastus lateralis based on near infrared spectrophotometry (50.3 vs 74.9 vs 60.4% of maximal desaturation during cuff ischemia). The results were supported by greater desaturation with smaller knee angles during static exercise and by greater desaturation and accelerated blood lactate accumulation during on-ice speed skating in the low vs high position. The results of this study support the hypothesis that physiological responses during speed skating are dominated by restriction of blood flow, attributable either to high intramuscular forces, the long duty cycle of the skating stroke, or both.

Adult↗

PubMed1998

Energy cost of rifle carriage in biathlon skiing.

PURPOSE: Since biathlon racing involves cross-country skiing while carrying a minimum weight 3.5-kg rifle, energy cost for rifle carriage could be significant to race outcome. The purposes of this study were to: 1) compare physiological measurements of biathletes roller skiing with and without rifle carriage, 2) compare energy cost of rifle carriage between women and men, 3) examine the relationship of cycle length and cycle rate to energy cost of rifle carriage, and 4) compare physiological measurements to calculated estimates of power requirements of rifle carriage. METHODS: We examined metabolic cost of rifle carriage during inclined roller ski-skating. National Team Biathletes (7 W, 8 M) performed treadmill roller ski-skating (2.46, 2.68, and 2.91 m.s-1, 8% incline, 5-min stages) with and without a 3.65 kg rifle. RESULTS: For W, HR, VO2, and VE during carriage were higher at all speeds, LA was higher at the fastest speed (P < 0.05). For M, VO2 and VE were higher at all speeds, HR and LA were higher at 2.68 and 2.91 m.s-1 (P < 0.05). Rifle mass as percent of body mass was different between W and M (6.6 +/- 0.7% vs 5.0 +/- 0.3%, P < 0.05). Percent increase in VO2 (2.1% and 1.3% per kg load; for W and M, respectively) was not different than rifle mass as percent body wt. Cycle length was related to increased VO2 and LA during rifle carriage for W (r = -0.59 and -0.70 to -0.85), and to LA for M (r = -0.66 to -0.83). CONCLUSION: The large range in cost between individuals (0.2 +/- 0.08 and 0.19 +/- 0.17 L.min-1; for W & M, respectively) suggests that individual economies for load carriage can be improved.

Adolescent↗

PubMed1997

Hemoglobin/myoglobin desaturation during speed skating.

The characteristic low "sitting" position of competitive speed skating has been shown to result in a right shifted heart rate-VO2 curve and elevated submaximal blood lactate values compared with running or cycling. This is thought to be a consequence of reduced blood flow and subsequent oxygen delivery to the exercising muscle while speed skating. Duel wavelength spectrophotometry was used to measure oxygenated and deoxygenated hemoglobin/myoglobin (OD) in the capillary bed of five muscle groups during in-line skating in upright (US) and low (LS) positions. Eight U.S. speed skaters (4 category 1) performed US and LS at 2.68 and 3.13 m.s-1 (4% grade) on a wide (2.44 m) treadmill (4 trials, 5 min each, 20 min recovery between trials). Expired gas parameters and blood lactate (LA) concentrations were determined for each trial. Hip and knee angles were measured (PEAK Motion Analysis) and were significantly different in US and LS. For similar oxygen uptake during US and LS (44.9 +/- 2.79, 45.6 +/- 3.52), heart rate and LA were significantly higher during LS (172 +/- 11 vs 179 +/- 10, 4.35 +/- 2.19 vs 8.70 +/- 3.60). Deoxygenation was significantly greater during LS than during US at both speeds and was greater at 3.13 m.s-1 (P < 0.05). OD was highly related to LA (r > 0.95) but not to whole body VO2. Blood volume change was less for LS than for US (P < 0.05). Increased deoxygenation in the capillary bed of the exercising quadriceps during LS versus US is consistent with the hypothesis that blood flow and subsequent O2 delivery is compromised in the low speed skating position.

Adolescent↗

PubMed1996

Compromised oxygen uptake in speed skaters during treadmill in-line skating.

The "sitting" posture of speed skating may result in compromised blood flow to the working muscles, thus limiting oxygen uptake. To examine this metabolic problem, male (N = 7) short track speed skaters performed running (TR), in-line skating upright (US), and in-line skating in the "sitting" position (LS) on a motor driven treadmill on randomized days. Each test consisted of four 4-min stages at 2.24, 2.68, 3.13, and 3.58 m.s-1 (5, 6, 7, and 8 mph) at 5% incline. After a brief rest, athletes performed at 4.03 m.s-1 (9 mph) with elevation increasing 1% each minute to exhaustion. Two on-ice 1000-m time trials (TT) were performed to assess the relationship between performance and laboratory measurements. Peak VO2 was lower during LS (57.2 +/- 2.7, 62.3 +/- 4.0, and 64.3 +/- 1.6; for LS, US, and TR, respectively; P < 0.05). At equivalent speeds, submaximal O2 uptake was lower for LS and blood lactate was higher (P < 0.05). LS peak VO2 (ml.kg-1.min-1) was strongly related to TT (P < 0.05). The depressed VO2 and higher blood lactate during LS may be related to decreased knee or trunk angle. Peak VO2 values during skating did not approach values during running. Evaluation of speed skaters in a sports-specific test is congruent with performance and demonstrates potential in addressing the unique physiological demands of the sport.

Adolescent↗

PubMed1996

Kinematics of cross-country ski racing.

This study investigated the evolution of skiing velocity, cycle length, and cycle rate in elite and subelite skiers during cross-country ski races. Senior male cross-country skiers engaged respectively in a 30-km skating race (N = 34) or a 50-km classical race (N = 27) were videotaped as they skied two different sections of 30 m, a 7 degrees uphill, and a flat section. In the skating race, most skiers used the offset technique on uphill and the 2-skate on flat, while the preferred techniques during the classical race were the diagonal stride for uphill and double-poling on flat. Results demonstrated that faster skiers had longer cycle lengths than slower skiers except for the flat sections of the classical race. Cycle rate was not different between skiers of different performance levels in any circumstances or races. Decreased velocity observed during the second half of the skating race was almost entirely due to a decrease in cycle length. We conclude that slower athletes should emphasize extending cycle length during their technical training. Therefore, skiers should place an emphasis on strength and power training to increase their kick and pole pushes and enhance cycle length.

Biomechanical Phenomena↗

PubMed1996

Effects of drafting during short-track speed skating.

Short-track speed skating involves pack-style racing where five to seven skaters may be on the ice at once. Since average speed for a 3000-m event may exceed 35 km.h-1, drafting may be beneficial. However, the short (111 m) oval track could limit effective drafting space, and high forces required in cornering may compromise potential benefits. We evaluated heart rate (HR)-lactate (LA) responses and post-drafting 3-lap sprint performance using 18 National Team and developmental skaters. Two 4-min trials, one drafting and one leading at 8.8 m.s-1, were performed. In addition, six skaters performed three 3-lap sprints, rested, immediately after a 4-min drafting trial at 9.2 m.s-1, and immediately after an unaided 4-min trial at 9.2 m.s-1. Results demonstrated lower HR and LA responses during drafting (174.0 +/- 9.0 and 5.56 +/- 2.18 vs 180.4 +/- 8.7 and 7.75, P < 0.05) at 8.8 m.s-1. After 4-min trials at 9.2 m.s-1, HR deltas were 6 bpm, lactate values were 9.00 +/- 1.84 and 5.22 +/- 1.18 for unaided and drafting, respectively. Sprint performance was better following drafting (33.46 +/- 1.19 vs 34.03 s, P < 0.05). HR and LA deltas during the 8.8 m.s-1 trials ranged from 0.8 to 12.4 and -0.18 to 5.37, respectively, indicating that some skaters were more effective drafters than others. These results suggest that drafting could be an important strategy in short-track speed skating, and drafting technique should be emphasized in training.

Air Movements↗

PubMed1996

Effect of kinematic variables on performance in women during a cross-country ski race.

The purpose of this study was to investigate the relationship of uphill cycle velocity, cycle length, and cycle rate in top U.S. female skiers during a multiple lap cross-country ski skating race. Eighteen female cross-country skiers served as subjects at the United States Women's 10-km Freestyle 1995 National Championships. The course consisted of two laps of the same 5-km loop. The selected filming section was an 11-12% uphill grade approximately 400 m long located at the 2.5- and 7.5-km mark. The video sector was approximately 12 m long at the conclusion of the climb. During the climb, the skating technique used by all skiers was the V-1. The results demonstrated that cycle length is positively related to cycle velocity during uphill ski skating and ultimately translates to faster race times by female cross-country ski racers. Lap 2 cycle velocity and cycle length demonstrated the strongest relationship to lap time and total race time. Moreover, cycle rate was not related to cycle velocity or lap race times and was not different between successful and less successful skiers. The slower climbing velocity noted during the latter half of the 10-km race was a consequence of a decreased cycle length and not cycle rate. This suggests that the degree of physical conditioning could be a factor in the ability to maintain cycle length and thus uphill cycle velocity.

Adolescent↗

PubMed1996

Creatine analogue beta-guanidinopropionic acid alters skeletal muscle AMP deaminase activity.

Dietary supplementation of the creatine analogue beta-guanidinopropionic acid (beta-GPA) decreases in vitro skeletal muscle AMP deaminase (AMP-D) activity in rats. Downregulation of AMP-D activity was progressive and greater in fast-twitch muscles (70-80%) than in the slow-twitch soleus muscle (approximately 50%). The loss in AMP-D activity had little effect on inosine 5'-monophosphate accumulation in mixed-fiber muscle with intense tetanic contractions. In contrast, inosine 5'-monophosphate formation was evident earlier in fast-twitch red and white fiber sections of creatine-depleted animals during intense twitch contractions, indicating that fast-twitch muscle of beta-GPA-treated rats buffers decreases in the ATP/ADPfree ratio via deamination, even though AMP-D activity is less. Isoforms of skeletal muscle AMP-D mRNAs in mixed-fiber muscle were not altered by feeding beta-GPA for up to 9 wk. Creatine depletion did not alter total immunoreactivity; however, a redistribution of AMP-D immunoreactivity from primarily an approximately 80-kDa form toward lower apparent molecular mass species (approximately 60 and approximately 56 kDa) was observed. Posttranslational changes in AMP-D appear related to changes in activity.

AMP Deaminase↗

PubMed1996

IMP reamination to AMP in rat skeletal muscle fiber types.

Inosine 5'-monophosphate (IMP) reamination in skeletal muscle fiber sections of the rat hindlimb was studied. High IMP concentrations were established during ischemic contractions in each fiber section: 3.1, 2.8, or 0.6 mumol/g in the fast-twitch white (FTW), fast-twitch red (FTR), and slow-twitch red (STR) muscle sections, respectively. Thereafter blood flow was restored and stimulation was discontinued to allow reamination of IMP. After 0, 2, 5, 10, 15, or 20 min of recovery, muscle sections were freeze-clamped and analyzed for metabolite contents. IMP was nearly fully reaminated after 10 and 20 min of recovery in STR and FTR muscles, respectively. Reamination in TW fibers was delayed and slower, with only 50% of the IMP reaminated after 20 min of recovery. Significant recovery (approximately 75%) of phosphocreatine occurs in each fiber section before the onset of reamination. Reamination was also evaluated after high-speed treadmill running with or without inhibition of reamination by hadacidin. Running resulted in large accumulations of IMP in FTW and FTR fibers (3.5 and 1.4 mumul/g, respectively); IMP in FTR fibers was higher with hadacidin treatment. Reamination after running was much greater in FTR than in FTW fibers and was associated with recovery of phosphocreatine. After running, the purine degradation products inosine and hypoxanthine were increased in FTW and FTR fibers in normal and hadacidin-treated animals. Plasma inosine, hypoxanthine, and urate increased after exercise; concentrations continued to increase if reamination was inhibited by hadacidin. These results demonstrate that when muscle IMP is increased, subsequent degradation and loss of purines occur. Rapid reamination should minimize the quantity of purine lost from muscle and limit the metabolic cost of replenishing purines by the de novo synthesis or salvage pathways.

Adenosine Monophosphate↗

PubMed1995

Physiological responses of speed skaters to treadmill low walking and cycle ergometry.

Speed skaters have previously relied on cycle ergometry for physiological testing. Current evidence suggests skate-specific testing might be more appropriate. Unlike cycling, skating and off-ice low walk training involves a 'crouched' posture, placing the quadriceps in static contraction. This may compromise blood flow to working muscles and influence VO2. We compared physiological variables between skate-specific treadmill low walking (LW) and cycle ergometry (BK). Skaters (N = 8) performed LW and BK to fatigue in randomized order. No difference existed for peak HR. Peak VO2 was lower for LW (4.13 +/- 0.34 vs 4.43 +/- 0.35, p < 0.05). Peak VE was lower during LW (146 +/- 13 vs 180 +/- 31, p < 0.05). R was significantly lower for LW, although no difference in peak lactate (LA) was evident. At submaximal heart rates, VO2 was lower during LW (p < 0.05), and submaximal LA was higher when expressed as percent peak VO2 (p < 0.05). These results are consistent with the hypothesis that skating posture limits O2 delivery to the lower extremities, and thus accounts for a greater dependence upon anaerobic energy production.

Adult↗