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  • 1
    Online Resource
    Online Resource
    A metabolic basis for impaired muscle force production and neuromuscular compensation during sprint cycling
    American Physiological Society ; 2006
    In:  American Journal of Physiology-Regulatory, Integrative and Comparative Physiology Vol. 291, No. 5 ( 2006-11), p. R1457-R1464
    Details
    In: American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, American Physiological Society, Vol. 291, No. 5 ( 2006-11), p. R1457-R1464
    Abstract: For both different individuals and modes of locomotion, the external forces determining all-out sprinting performances fall predictably with effort duration from the burst maximums attained for 3 s to those that can be supported aerobically as trial durations extend to roughly 300 s. The common time course of this relationship suggests a metabolic basis for the decrements in the force applied to the environment. However, the mechanical and neuromuscular responses to impaired force production (i.e., muscle fatigue) are generally considered in relation to fractions of the maximum force available, or the maximum voluntary contraction (MVC). We hypothesized that these duration-dependent decrements in external force application result from a reliance on anaerobic metabolism for force production rather than the absolute force produced. We tested this idea by examining neuromuscular activity during two modes of sprint cycling with similar external force requirements but differing aerobic and anaerobic contributions to force production: one- and two-legged cycling. In agreement with previous studies, we found greater peak per leg aerobic metabolic rates [59% (±6 SD)] and pedal forces at V̇o 2 peak [30% (±9)] during one- vs. two-legged cycling. We also determined downstroke pedal forces and neuromuscular activity by surface electromyography during 15 to 19 all-out constant load sprints lasting from 12 to 400 s for both modes of cycling. In support of our hypothesis, we found that the greater reliance on anaerobic metabolism for force production induced compensatory muscle recruitment at lower pedal forces during two- vs. one-legged sprint cyc ling. We conclude that impaired muscle force production and compensatory neuromuscular activity during sprinting are triggered by a reliance on anaerobic metabolism for force production.
    Type of Medium: Online Resource
    ISSN: 0363-6119 , 1522-1490
    URL: Article
    DOI: 10.1152/ajpregu.00108.2006
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2006
    detail.hit.zdb_id: 1477297-8
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  • 2
    Online Resource
    Online Resource
    High-speed running performance is largely unaffected by hypoxic reductions in aerobic power
    American Physiological Society ; 1999
    In:  Journal of Applied Physiology Vol. 86, No. 6 ( 1999-06-01), p. 2059-2064
    Details
    In: Journal of Applied Physiology, American Physiological Society, Vol. 86, No. 6 ( 1999-06-01), p. 2059-2064
    Abstract: We tested the importance of aerobic metabolism to human running speed directly by altering inspired oxygen concentrations and comparing the maximal speeds attained at different rates of oxygen uptake. Under both normoxic (20.93% O 2 ) and hypoxic (13.00% O 2 ) conditions, four fit adult men completed 15 all-out sprints lasting from 15 to 180 s as well as progressive, discontinuous treadmill tests to determine maximal oxygen uptake and the metabolic cost of steady-state running. Maximal aerobic power was lower by 30% (1.00 ± 0.15 vs. 0.77 ± 0.12 ml O 2 ⋅ kg −1 ⋅ s −1 ) and sprinting rates of oxygen uptake by 12–25% under hypoxic vs. normoxic conditions while the metabolic cost of submaximal running was the same. Despite reductions in the aerobic energy available for sprinting under hypoxic conditions, our subjects were able to run just as fast for sprints of up to 60 s and nearly as fast for sprints of up to 120 s. This was possible because rates of anaerobic energy release, estimated from oxygen deficits, increased by as much as 18%, and thus compensated for the reductions in aerobic power. We conclude that maximal metabolic power outputs during sprinting are not limited by rates of anaerobic metabolism and that human speed is largely independent of aerobic power during all-out runs of 60 s or less.
    Type of Medium: Online Resource
    ISSN: 8750-7587 , 1522-1601
    URL: Article
    DOI: 10.1152/jappl.1999.86.6.2059
    RVK:
    WA 15000
    RVK:
    XA 52094
    Language: English
    Publisher: American Physiological Society
    Publication Date: 1999
    detail.hit.zdb_id: 1404365-8
    SSG: 12
    SSG: 31
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  • 3
    Online Resource
    Online Resource
    Influence of duty cycle on the time course of muscle fatigue and the onset of neuromuscular compensation during exhaustive dynamic isolated limb exercise
    American Physiological Society ; 2015
    In:  American Journal of Physiology-Regulatory, Integrative and Comparative Physiology Vol. 309, No. 1 ( 2015-07-01), p. R51-R61
    Details
    In: American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, American Physiological Society, Vol. 309, No. 1 ( 2015-07-01), p. R51-R61
    Abstract: We investigated the influence of altered muscle duty cycle on the performance decrements and neuromuscular responses occurring during constant-load, fatiguing bouts of knee extension exercise. We experimentally altered the durations of the muscularly inactive portion of the limb movement cycle and hypothesized that greater relative durations of inactivity within the same movement task would 1) reduce the rates and extent of muscle performance loss and 2) increase the forces necessary to trigger muscle fatigue. In each condition (duty cycle = 0.6 and 0.3), male subjects [age = 25.9 ± 2.0 yr (SE); mass = 85.4 ± 2.6 kg], completed 9–11 exhaustive bouts of two-legged knee extension exercise, at force outputs that elicited failure between 4 and 290 s. The novel duty cycle manipulation produced two primary results; first, we observed twofold differences in both the extent of muscle performance lost (DC 0.6 = 761 ± 35 N vs. DC 0.3 = 366 ± 49 N) and the time course of performance loss. For example, exhaustive trials at the midpoint of these force ranges differed in duration by more than 30 s ( t 0.6 = 36 ± 2.6 vs. t 0.3 = 67 ± 4.3 s). Second, both the minimum forces necessary to exceed the peak aerobic capacity and initiate a reliance on anaerobic metabolism, and the forces necessary to elicit compensatory increases in electromyogram activity were 300% greater in the lower vs. higher duty cycle condition. These results indicate that the fatigue-induced compensatory behavior to recruit additional motor units is triggered by a reliance on anaerobic metabolism for ATP resynthesis and is independent of the absolute level or fraction of the maximum force produced by the muscle.
    Type of Medium: Online Resource
    ISSN: 0363-6119 , 1522-1490
    URL: Article
    DOI: 10.1152/ajpregu.00356.2014
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2015
    detail.hit.zdb_id: 1477297-8
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  • 4
    Online Resource
    Online Resource
    High-speed running performance: a new approach to assessment and prediction
    American Physiological Society ; 2003
    In:  Journal of Applied Physiology Vol. 95, No. 5 ( 2003-11), p. 1955-1962
    Details
    In: Journal of Applied Physiology, American Physiological Society, Vol. 95, No. 5 ( 2003-11), p. 1955-1962
    Abstract: We hypothesized that allout running speeds for efforts lasting from a few seconds to several minutes could be accurately predicted from two measurements: the maximum respective speeds supported by the anaerobic and aerobic powers of the runner. To evaluate our hypothesis, we recruited seven competitive runners of different event specialties and tested them during treadmill and overground running on level surfaces. The maximum speed supported by anaerobic power was determined from the fastest speed that subjects could attain for a burst of eight steps (∼3 s or less). The maximum speed supported by aerobic power, or the velocity at maximal oxygen uptake, was determined from a progressive, discontinuous treadmill test to failure. All-out running speeds for trials of 3-240 s were measured during 10-13 constant-speed treadmill runs to failure and 4 track runs at specified distances. Measured values of the maximum speeds supported by anaerobic and aerobic power, in conjunction with an exponential constant, allowed us to predict the speeds of all-out treadmill trials to within an average of 2.5% ( R 2 = 0.94; n = 84) and track trials to within 3.4% ( R 2 = 0.86; n = 28). An algorithm using this exponent and only two of the all-out treadmill runs to predict the remaining treadmill trials was nearly as accurate (average = 3.7%; R 2 = 0.93; n = 77). We conclude that our technique 1) provides accurate predictions of high-speed running performance in trained runners and 2) offers a performance assessment alternative to existing tests of anaerobic power and capacity.
    Type of Medium: Online Resource
    ISSN: 8750-7587 , 1522-1601
    URL: Article
    DOI: 10.1152/japplphysiol.00921.2002
    RVK:
    WA 15000
    RVK:
    XA 52094
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2003
    detail.hit.zdb_id: 1404365-8
    SSG: 12
    SSG: 31
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  • 5
    Online Resource
    Online Resource
    Rates of performance loss and neuromuscular activity in men and women during cycling: evidence for a common metabolic basis of muscle fatigue
    American Physiological Society ; 2017
    In:  Journal of Applied Physiology Vol. 122, No. 1 ( 2017-01-01), p. 130-141
    Details
    In: Journal of Applied Physiology, American Physiological Society, Vol. 122, No. 1 ( 2017-01-01), p. 130-141
    Abstract: The durations that muscular force and power outputs can be sustained until failure fall predictably on an exponential decline between an individual’s 3-s burst maximum to the maximum performance they can sustain aerobically. The exponential time constants describing these rates of performance loss are similar across individuals, suggesting that a common metabolically based mechanism governs muscle fatigue; however, these conclusions come from studies mainly on men. To test whether the same physiological understanding can be applied to women, we compared the performance-duration relationships and neuromuscular activity between seven men [23.3 ± 1.9 (SD) yr] and seven women (21.7 ± 1.8 yr) from multiple exhaustive bouts of cycle ergometry. Each subject performed trials to obtain the peak 3-s power output (P max ), the mechanical power at the aerobic maximum (P aer ), and 11–14 constant-load bouts eliciting failure between 3 and 300 s. Collectively, men and women performed 180 exhaustive bouts spanning an ~6-fold range of power outputs (118–1116 W) and an ~35-fold range of trial durations (8–283 s). Men generated 66% greater P max (956 ± 109 W vs. 632 ± 74 W) and 68% greater P aer (310 ± 47 W vs. 212 ± 15 W) than women. However, the metabolically based time constants describing the time course of performance loss were similar between men (0.020 ± 0.003/s) and women (0.021 ± 0.003/s). Additionally, the fatigue-induced increases in neuromuscular activity did not differ between the sexes when compared relative to the pedal forces at P aer . These data suggest that muscle fatigue during short-duration dynamic exercise has a common metabolically based mechanism determined by the extent that ATP is resynthesized by anaerobic metabolism. NEW & NOTEWORTHY Although men and women differed considerably in their absolute cycling performances, there was no sex difference in the metabolically based exponential time constant that described the performance-duration relationship. Similarly, the fatigue-induced increases in neuromuscular activity were not different between the sexes when compared from a metabolic perspective. These data suggest that men and women have similar rate-limiting mechanisms for short-duration dynamic exercise that are determined by the extent the exercise is supported by anaerobic metabolism.
    Type of Medium: Online Resource
    ISSN: 8750-7587 , 1522-1601
    URL: Article
    DOI: 10.1152/japplphysiol.00468.2016
    RVK:
    WA 15000
    RVK:
    XA 52094
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2017
    detail.hit.zdb_id: 1404365-8
    SSG: 12
    SSG: 31
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  • 6
    Online Resource
    Online Resource
    Metabolic And Cardiovascular Alterations During Critical Training In Wildland Firefighters : 2946 Board #6 May 29 1:00 PM - 3:00 PM
    Ovid Technologies (Wolters Kluwer Health) ; 2020
    In:  Medicine & Science in Sports & Exercise Vol. 52, No. 7S ( 2020-7), p. 816-816
    Details
    In: Medicine & Science in Sports & Exercise, Ovid Technologies (Wolters Kluwer Health), Vol. 52, No. 7S ( 2020-7), p. 816-816
    Type of Medium: Online Resource
    ISSN: 1530-0315 , 0195-9131
    URL: Article
    DOI: 10.1249/01.mss.0000684308.74831.79
    RVK:
    ZX 1000
    Language: English
    Publisher: Ovid Technologies (Wolters Kluwer Health)
    Publication Date: 2020
    detail.hit.zdb_id: 2031167-9
    SSG: 31
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  • 7
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    Online Resource
    Muscle Soreness And Damage During Wildland Firefighter Critical Training : 1424 Board #18 May 28 9:30 AM - 11:00 AM
    Ovid Technologies (Wolters Kluwer Health) ; 2020
    In:  Medicine & Science in Sports & Exercise Vol. 52, No. 7S ( 2020-7), p. 370-370
    Details
    In: Medicine & Science in Sports & Exercise, Ovid Technologies (Wolters Kluwer Health), Vol. 52, No. 7S ( 2020-7), p. 370-370
    Type of Medium: Online Resource
    ISSN: 1530-0315 , 0195-9131
    URL: Article
    DOI: 10.1249/01.mss.0000677820.53619.cb
    RVK:
    ZX 1000
    Language: English
    Publisher: Ovid Technologies (Wolters Kluwer Health)
    Publication Date: 2020
    detail.hit.zdb_id: 2031167-9
    SSG: 31
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  • 8
    Online Resource
    Online Resource
    Mechanics of wing-assisted incline running (WAIR)
    The Company of Biologists ; 2003
    In:  Journal of Experimental Biology Vol. 206, No. 24 ( 2003-12-15), p. 4553-4564
    Details
    In: Journal of Experimental Biology, The Company of Biologists, Vol. 206, No. 24 ( 2003-12-15), p. 4553-4564
    Abstract: A recently discovered locomotor behavior, wing-assisted incline running(WAIR), allows fully volant animals to `run' up vertical obstacles. Such a task would appear to be especially formidable for bipeds, yet WAIR is used preferentially by ground-dwelling birds, specifically chukar partridge Alectoris chukar, to reach refugia. The basic locomotor mechanics that enable this behavior are not fully understood. For instance, are there functional differences at the level of the wing during WAIR and free flight,and do the hindlimbs actively participate in propulsion during WAIR? To investigate wing function during these activities we used accelerometry to compare the instantaneous whole-body acceleration during WAIR and ascending free flights at a similar climb angle. Throughout a substantial portion of the wingbeat cycle, chukars engaged in WAIR experienced an acceleration oriented towards the substrate, whereas during ascending free flights the acceleration of the center of mass was parallel to the direction of travel. We investigated whether the animals were using their hindlimbs for propulsion, rather than for some other function (e.g. to maintain balance), by measuring ground reaction forces (GRF) during bouts of WAIR. Estimates of the contribution of the hindlimbs towards the vertical external work done by the bird were 98±8% of the total at an incline of 60° (the steepest angle that birds were able to negotiate without the use of their forelimbs). During vertical (90°) bouts of WAIR the hindlimb contribution was 37±5% of the total external work. Yet, the magnitude of the peak GRF at 90° was 175% of the value generated during level walking, revealing that birds engaged in WAIR do generate sizeable hindlimb forces even during vertical ascents. These data support the hypothesis that forelimbs are enabling hindlimb function, and we argue that this represents a locomotor strategy which may have been used by proto-birds during the evolution of flight.
    Type of Medium: Online Resource
    ISSN: 1477-9145 , 0022-0949
    URL: Article
    DOI: 10.1242/jeb.00673
    Language: English
    Publisher: The Company of Biologists
    Publication Date: 2003
    detail.hit.zdb_id: 1482461-9
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  • 9
    Online Resource
    Online Resource
    High metabolic rates in running birds
    Springer Science and Business Media LLC ; 1999
    In:  Nature Vol. 397, No. 6714 ( 1999-1), p. 31-32
    Details
    In: Nature, Springer Science and Business Media LLC, Vol. 397, No. 6714 ( 1999-1), p. 31-32
    Type of Medium: Online Resource
    ISSN: 0028-0836 , 1476-4687
    URL: Article
    DOI: 10.1038/16173
    RVK:
    TA 1000
    RVK:
    UA 1000
    RVK:
    WA 15000
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 1999
    detail.hit.zdb_id: 120714-3
    detail.hit.zdb_id: 1413423-8
    SSG: 11
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  • 10
    Online Resource
    Online Resource
    Last Word on Point:Counterpoint: Artificial limbs do make artificially fast running speeds possible
    American Physiological Society ; 2010
    In:  Journal of Applied Physiology Vol. 108, No. 4 ( 2010-04), p. 1019-1019
    Details
    In: Journal of Applied Physiology, American Physiological Society, Vol. 108, No. 4 ( 2010-04), p. 1019-1019
    Type of Medium: Online Resource
    ISSN: 8750-7587 , 1522-1601
    URL: Article
    DOI: 10.1152/japplphysiol.00149.2010
    RVK:
    WA 15000
    RVK:
    XA 52094
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2010
    detail.hit.zdb_id: 1404365-8
    SSG: 12
    SSG: 31
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