Effects of Mode of Contraction on Neuromuscular Fatigue

Effects of Mode of Contraction on Neuromuscular Fatigue in Young People Aged 18 to 35, Aged 60 to 80 and Very Old People Aged Over 80

Aging is associated with multiple deteriorations of the neuromuscular system. Given the increase in life expectancy, the investigators can now distinguish old adults (>60 years old) who conserve their neuromuscular capacities with regular physical activity and very old adults (>80 years old) who suffer from an inexorable decline, even if the number of octogenarians and their quality of life are progressively increasing. However, the most part of the literature on fatigue and neuromuscular capacity with aging focused on isometric tasks. The results showed a significant decrease in maximal force production capacity and a greater resistance to fatigue for old people compared to the young population. When fatigue is induced trough dynamic contractions, greater fatigability was observed in old adults compared to young adults. Investigations performed on the population aged over 80 years old are rare, showing greater fatigability in octogenarians than old men (aged 60-80 years old) during isometric tasks. The knowledge about the effects of dynamic contractions in this population are limited, and performed uniquely in single leg isokinetic mode. Evaluations that require the use of both legs and higher muscle mass involved in the task (cycloergometer) are needed. Understanding neuromuscular fatigue and fatigability across different exercise modalities is necessary to set adapted physical activity programs aimed to maintain autonomy in older individuals.

Inclusion Criteria:

• Belong to a defined age group: young (18 to 35 years old inclusive), old (60 to 80 years old inclusive) and very old (81 to 95 years old inclusive),
• Signed written consent form
• Being affiliated to social security

Exclusion Criteria:

• Pathology or surgery resulting in a locomotor disorder, within 6 months prior to the study,
• Chronic neurological, motor or psychological pathologies
• Use of neuro-active substances likely to alter cortico-spinal excitability (hypnotics, antiepileptics, psychotropic drugs, muscle relaxants) for the duration of the study.
• Contraindication to magnetic stimulation:
• Cardiac or respiratory insufficiency.
• Cardiac pacemaker.
• Cardiac valve wear and serious cardiovascular diseases.
• Presence of prosthetic material or ferromagnetic foreign bodies in the head.
• Presence of cochlear implants or ocular prosthetic material.
• History of neurosurgical interventions.
• Neurological diseases that may affect brain structures and cognitive abilities (e.g., intracranial tumour, multiple sclerosis, history of stroke or traumatic brain injury).
• History of comitiality, contralateral knee pathology or pathology of the musculoskeletal system.
• Mini Mental State Examination < 20