Author(s): MARTIRE, F., LECCE, E.1, GRECO, G.1, AMORUSO, P.1, BAZZUCCHI, I.1, SCOTTO DI PALUMBO, A.1, SACCHETTI, M.1 , Institution: UNIVERSITY OF ROME 'FORO ITALICO', Country: ITALY, Abstract-ID: 1663

INTRODUCTION:
The ability to rapidly generate force is essential for daily movements and balance recovery following external perturbations. Because the time available to produce force in real-world scenarios is typically less than 250 ms, insufficient for the full expression of maximal strength, the rate of force development (RFD) becomes a critical determinant of balance recovery and fall prevention and declines considerably with ageing [1]. Individuals with type 2 diabetes (T2D) exhibit an even greater impairment in RFD, indicative of early neuromuscular impairment that can occur even in the absence of clinically evident complications [2]. During ballistic contractions, motor unit recruitment rate (MU-Rr) and maximal discharge rate (DRMAX) predict maximal-RFD (RFDmax) and impulse in young adults [3]. However, the neural mechanisms underlying reduced RFD in older adults with and without T2D remain unknown. This investigation aimed to determine whether age- and T2D-related reductions in RFD were mediated by alterations in these functional neural determinants.
METHODS:
Ten healthy older adults (62±5 yrs, BMI 24.31 ± 4.39 kg ⋅ m-2) and ten older adults with T2D (63±4 yrs, BMI 28.07 ± 4.03 kg ⋅ m-2) were enrolled in this study and compared to ten young adults (23±3 yrs, BMI 27.33 ± 4.08 kg ⋅ m-2). Participants performed ballistic isometric contractions of the ankle dorsiflexors to quantify RFDmax and impulse, while high-density surface EMG was recorded to examine MU-Rr and DRMAX, following validated approaches [3].
RESULTS:
Compared with young controls, RFDmax was significantly lower in older individuals (-1034 N⋅s-1, p=0.002), with greater reductions in T2D (-1715 N⋅s-1, p<0.001). Similarly, impulse was reduced in the old (-12.6 N⋅s, p=0.03) and T2D groups (-25.9 N⋅s, p<0.001). These functional deficits were accompanied by proportional reductions in MU-Rr (p<0.001) and DRMAX (p<0.01), with impairments more pronounced in T2D than in healthy old adults (p<0.01). Importantly, MU-Rr and DRMAX correlated with RFDmax (R2>0.55, p<0.01) and impulse (R2>0.50, p<0.01) in all groups.
CONCLUSION:
To our knowledge, these results provide the first direct evidence that impairment of rapid force capacity with ageing and even more with T2D is associated with a proportional slowing of MU-Rr and reduced DRMAX, reflecting an impaired descending excitatory drive from the central nervous system [2,3], and identify these neural changes as primary limitations to rapid force capacity and biomarkers to target in specific rehabilitation settings. This limitation likely compromises the ability to produce corrective torque during balance disturbances and may contribute to increased fall risk, identifying rapid force activation as an important target for rehabilitation strategies.

REFERENCES:
[1] https://doi.org/10.1113/JP285667
[2] https://doi.org/10.1113/JP287589
[3] https://doi.org/10.1113/JP277396