Supplementary file 1_Bed rest and endurance retraining alter persistent inward current estimates in young and older males.docx

After retraining, ΔF was no longer different from baseline in YA, whereas in OA values at RT did not differ from either baseline or bed rest. In YA, ACC (-25.1%, p=0.002) and ATT (-27.7%, p=0.023), but not BH, decreased after bed rest and were no longer different from baseline after retraining; in OA, BH, ACC, and ATT were unchanged. Peak discharge rate and discharge-rate range decreased after bed rest in both groups and showed partial recovery after retraining.

Plasma tryptophan, kynurenine, and their ratio did not change.</p>Discussion<p>These findings indicate that motoneuron-related indices are sensitive to prolonged physical inactivity and remain modifiable during post-disuse retraining. Although older adults were exposed to a shorter bed rest duration, ΔF adaptations to disuse and retraining were also present in an older population. The non-uniform behavior of ΔF and geometric discharge metrics suggests that different aspects of motoneuron output may adapt through partly distinct mechanisms, potentially with age-dependent features.</p>