Author(s): DESACHY, M.1,2, HERAUD, N.2, LAGARDE, J.1, VARRAY, A.1, Institution: UNIVERSITÉ DE MONTPELLIER, Country: FRANCE, Abstract-ID: 1760

INTRODUCTION:
Eccentric (ECC) contractions generate greater force with lower metabolic cost and cardio-respiratory constraint than concentric (CON) ones. In 2004, through electroencephalography (EEG) analysis, Fang et al. highlight that ECC induce greater cortical activity during movement planning and execution than CON contractions and more specifically greater amplitude and latency movement-related cortical potentials (MRCP). Interestingly, this was observed either in sensory-motor area and others areas. These results indicate that the use of ECC contractions could be potentially highly relevant to fight against insufficient cortical activation significantly implicated in muscle weakness of older persons or COPD patients (1). However, these results were obtained in young subjects’ upper limbs, while cortico-muscle dysfunction mainly affects the lower limbs and older persons. Thus, the purpose of this study was to compare cortical activity during quadriceps CON and ECC contractions in young (20-35 years) vs. older (50-75 years) healthy participants.
METHODS:
17 young and 16 older participants (62 ± 7 and 23 ± 4 years respectively) performed 40 voluntary ECC and CON quadriceps contractions against 20% of their maximal isometric force on a Biodex isokinetic ergometer. Surface EEG signals from Cz electrode (more proximal area of quadriceps motor command) and 8 others overlying sensorimotor cortical areas, were recorded. MRCPs were derived from EEG signals in order to analyze the negative peak (NP). The amplitude and latency of the NP were calculated as indicators of cortical activation related to movement execution and planning respectively.
RESULTS:
As main result, Cz NP amplitude was greater during ECC contractions (p < 0.05, η2p = 0.13) for both groups (p = 0,48) despite systematic lower values in older group (p < 0.05, η2p = 0.24). As secondary results, only FC5 shows significant greater amplitude and latency during ECC contractions for both age group (p < 0.05, η2p = 0.26 and 0.20).
These results exhibit a higher cortical activity during ECC contractions whatever age, and a decreased cortical activity with aging. In addition, ECC contractions performed on the lower limbs are not associated with a higher activation extended to the whole cortex areas, as found in upper limb studies.
CONCLUSION:
Our study shows that despite an overall reduction in motor cortex activity involved in the lower limbs during aging, the higher activity during ECC contractions of the lower limbs always exists in the older group. Consequently, this raises the interest of eccentric training to induce higher cortical activity in older individuals or COPD patients to fight against the cortical component of muscle weakness.
REFERENCES:
(1) Alexandre et al. (2020) Specific motor cortex hypoexcitability and hypoactivation in COPD patients with peripheral muscle weakness. BMC Pulm. Med. 20, 1. https://doi.org/10.1186/s12890-019-1042-0