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To M1, Strutton P2, Alexander C1,2
1Imperial College Healthcare NHS Trust, Therapies, London, United Kingdom, 2Imperial College, Surgery and Cancer, London, United Kingdom
Background: Symptomatic Joint Hypermobility (SJH) is a disorder of connective tissue. Although the population incidence is low, it is high within UK musculoskeletal health services. People with SJH suffer with chronic joint pain and instability. The majority also suffer with fatigue of unknown origin, which is commonly overlooked as it does not feature in classification criteria. Fatigue causes distress and can have a bigger impact than pain on daily function. It is important to understand the origin of fatigue so we can develop targeted treatments.
Purpose: The origin of fatigue in this cohort is likely to be multi-faceted, involving both physiological and psychological aspects. The purpose of this study was to investigate the physiological contribution of central and peripheral fatigue. That is, the inability to maintain muscle output during a fatiguing muscle contraction that might originate from reduced central nervous system drive (central fatigue) or reduced force generating capacity of the muscle itself (peripheral fatigue).
Methods: With ethical approval and informed consent and after a sample size calculation, 12 people with SJH and 12 healthy controls were recruited. The Brighton Criteria were used to classify the SJH group. Central fatigue was investigated using the twitch interpolation technique where transcranial magnetic stimulation (TMS) over the motor cortex supplying biceps brachii (BB) was delivered and the subsequent electromyographic activity (EMG) and torque recorded. An increase in the size of the superimposed twitch during a sustained contraction is indicative of central fatigue. Amplitude of motor evoked potentials and time to peak amplitude of twitches were also measured. Peripheral fatigue was investigated using electrical stimulation of the musculocutaneous nerve to evoke motor responses in the relaxed BB. Background muscle activity was measured as root mean square amplitude of EMG. Central and peripheral fatigue were assessed during a control, fatiguing and recovery phase BB contraction protocol. The results of a verbal Borg Scale were collected, which assessed levels of exertion at the start of the control phase, before and immediately after the fatiguing phase and at the end of the recovery phase.
Results: The Borg Scale revealed that all participants felt fatigued during the protocol however, the SJH group felt greater fatigue and did not recover (p=0.005). MEP amplitude increased in the SJH group alone (p 0.01) during the fatiguing protocol before it recovered (p 0.01). Superimposed twitch amplitude increased in the SJH group during the fatiguing protocol and stayed elevated during the recovery phase (p 0.04) revealing central fatigue. This did not occur in the control group. Time to peak amplitude of the superimposed twitch generated by TMS was longer in the SJH group (p 0.05) suggesting a change to motor unit recruitment. Peripheral fatigue did not occur in either group.
Conclusion(s): During muscle contractions people with SJH suffered central fatigue. They also recruited motor units differently or had loss of faster motor units.
Implications: This knowledge guides exercise prescription, as central fatigue improves with high intensity strength training in other cohorts. However, a paced progression is recommended to moderate the risk of joint instability and increased pain.
Keywords: Joint Hypermobility, Hypermobile Ehlers Danlos Syndrome, Fatigue
Funding acknowledgements: MT: Pre-doctoral training fellowship; Imperial College Healthcare Charity.
CMA: Senior Clinical Lectureship from the National Institute of Health Research.
Purpose: The origin of fatigue in this cohort is likely to be multi-faceted, involving both physiological and psychological aspects. The purpose of this study was to investigate the physiological contribution of central and peripheral fatigue. That is, the inability to maintain muscle output during a fatiguing muscle contraction that might originate from reduced central nervous system drive (central fatigue) or reduced force generating capacity of the muscle itself (peripheral fatigue).
Methods: With ethical approval and informed consent and after a sample size calculation, 12 people with SJH and 12 healthy controls were recruited. The Brighton Criteria were used to classify the SJH group. Central fatigue was investigated using the twitch interpolation technique where transcranial magnetic stimulation (TMS) over the motor cortex supplying biceps brachii (BB) was delivered and the subsequent electromyographic activity (EMG) and torque recorded. An increase in the size of the superimposed twitch during a sustained contraction is indicative of central fatigue. Amplitude of motor evoked potentials and time to peak amplitude of twitches were also measured. Peripheral fatigue was investigated using electrical stimulation of the musculocutaneous nerve to evoke motor responses in the relaxed BB. Background muscle activity was measured as root mean square amplitude of EMG. Central and peripheral fatigue were assessed during a control, fatiguing and recovery phase BB contraction protocol. The results of a verbal Borg Scale were collected, which assessed levels of exertion at the start of the control phase, before and immediately after the fatiguing phase and at the end of the recovery phase.
Results: The Borg Scale revealed that all participants felt fatigued during the protocol however, the SJH group felt greater fatigue and did not recover (p=0.005). MEP amplitude increased in the SJH group alone (p 0.01) during the fatiguing protocol before it recovered (p 0.01). Superimposed twitch amplitude increased in the SJH group during the fatiguing protocol and stayed elevated during the recovery phase (p 0.04) revealing central fatigue. This did not occur in the control group. Time to peak amplitude of the superimposed twitch generated by TMS was longer in the SJH group (p 0.05) suggesting a change to motor unit recruitment. Peripheral fatigue did not occur in either group.
Conclusion(s): During muscle contractions people with SJH suffered central fatigue. They also recruited motor units differently or had loss of faster motor units.
Implications: This knowledge guides exercise prescription, as central fatigue improves with high intensity strength training in other cohorts. However, a paced progression is recommended to moderate the risk of joint instability and increased pain.
Keywords: Joint Hypermobility, Hypermobile Ehlers Danlos Syndrome, Fatigue
Funding acknowledgements: MT: Pre-doctoral training fellowship; Imperial College Healthcare Charity.
CMA: Senior Clinical Lectureship from the National Institute of Health Research.
Topic: Musculoskeletal; Rheumatology
Ethics approval required: Yes
Institution: National Research Ethics Service
Ethics committee: London - Queen Square Research Ethics Committee
Ethics number: Rec: 16/LO/0178 IRAS: 195348
All authors, affiliations and abstracts have been published as submitted.
