title: The relationship between exercise-induced muscle fatigue, arterial blood flow and muscle perfusion after 56 days local muscle unloading.
abstract: In the light of the dynamic nature of habitual plantar flexor activity, we utilized an incremental isokinetic exercise test (IIET) to assess the work-related power deficit (WoRPD) as a measure for exercise-induced muscle fatigue before and after prolonged calf muscle unloading and in relation to arterial blood flow and muscle perfusion. Eleven male subjects (31 ± 6 years) wore the HEPHAISTOS unloading orthosis unilaterally for 56 days. It allows habitual ambulation while greatly reducing plantar flexor activity and torque production. Endpoint measurements encompassed arterial blood flow, measured in the femoral artery using Doppler ultrasound, oxygenation of the soleus muscle assessed by near-infrared spectroscopy, lactate concentrations determined in capillary blood and muscle activity using soleus muscle surface electromyography. Furthermore, soleus muscle biopsies were taken to investigate morphological muscle changes. After the intervention, maximal isokinetic torque was reduced by 23·4 ± 8·2% (P<0·001) and soleus fibre size was reduced by 8·5 ± 13% (P = 0·016). However, WoRPD remained unaffected as indicated by an unchanged loss of relative plantar flexor power between pre- and postexperiments (P = 0·88). Blood flow, tissue oxygenation, lactate concentrations and EMG median frequency kinematics during the exercise test were comparable before and after the intervention, whereas the increase of RMS in response to IIET was less following the intervention (P = 0·03). In conclusion, following submaximal isokinetic muscle work exercise-induced muscle fatigue is unaffected after prolonged local muscle unloading. The observation that arterial blood flow was maintained may underlie the unchanged fatigability.
authors.affiliation: German Aerospace Center, Institute of Aerospace Medicine, Space Physiology, Cologne, Germany; Department of Molecular and Cellular Sport Medicine, German Sport University, Cologne, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Weber
authors.forename: Michel
authors.initials: M
authors.lastname: Ducos
authors.forename: Edwin
authors.initials: E
authors.lastname: Mulder
authors.forename: Åsa
authors.initials: Å
authors.lastname: Beijer
authors.forename: Frankyn
authors.initials: F
authors.lastname: Herrera
authors.forename: Jochen
authors.initials: J
authors.lastname: Zange
authors.forename: Hans
authors.initials: H
authors.lastname: Degens
authors.forename: Wilhelm
authors.initials: W
authors.lastname: Bloch
authors.forename: Jörn
authors.initials: J
authors.lastname: Rittweger
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D001783:Blood Flow Velocity; D005263:Femoral Artery / Q000000981:diagnostic imaging / Q000503:physiopathology*; D006801:Humans; D019344:Lactic Acid / Q000097:blood; D007866:Leg; D008297:Male; D009119:Muscle Contraction; D018763:Muscle Fatigue; D053580:Muscle Strength; D018482:Muscle, Skeletal / Q000098:blood supply* / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology*; D009133:Muscular Atrophy / Q000097:blood / Q000473:pathology / Q000503:physiopathology*; D009989:Orthotic Devices; D012039:Regional Blood Flow; D013997:Time Factors; D019415:Torque; D014463:Ultrasonography; D016474:Weight-Bearing
chemical_list: D019344:Lactic Acid
keywords: arterial blood flow; muscle fatigue; muscle perfusion; muscle power; muscle unloading