Obtaining true maximum voluntary excitation appears to be more difficult in older populations than in young populations. The aims of this study were (1) to determine whether differences in maximum voluntary excitation obtained from maximum voluntary isometric contraction (MVIC) and (sub-)maximum voluntary dynamic contraction [(s-)MVDC] are age dependent, and (2) to determine how normalizing electromyographic signals to corresponding maximum voluntary excitations affects variance between participants and the likelihood of normalized signals exceeding 100%. MVIC, s-MVDC, and MVDC were recorded in 10 young women, and MVIC and s-MVDC were recorded in 19 older women. A significant age × contraction mode interaction effect was found for vastus lateralis (P = .04). In young women, MVDC elicited the highest maximum voluntary excitation for vastus lateralis and rectus femoris (P < .05). In older women, no differences in maximum voluntary excitation were found (P > .05). Normalization to dynamic contractions resulted in lower between-participant variance of electromyography amplitudes, though not for all muscles, and decreased the number of normalized signals exceeding 100% in young women. These findings indicate that differences in maximum voluntary excitation across contraction modes are age dependent. Therefore, one should be cautious when comparing normalized signals between age groups; however, overall dynamic contractions may be preferable over isometric contractions for normalization purposes.
Remco J. Baggen, Jaap H. van Dieën, Sabine M. Verschueren, Evelien Van Roie and Christophe Delecluse
Kimberley S. van Schooten, Sietse M. Rispens, Petra J.M. Elders, Paul Lips, Jaap H. van Dieën and Mirjam Pijnappels
We investigated the reliability of physical activity monitoring based on trunk accelerometry in older adults and assessed the number of measured days required to reliably assess physical activity. Seventy-nine older adults (mean age 79.1 ± 7.9) wore an accelerometer at the lower back during two nonconsecutive weeks. The duration of locomotion, lying, sitting, standing and shuffling, movement intensity, the number of locomotion bouts and transitions to standing, and the median and maximum duration of locomotion were determined per day. Using data of week 2 as reference, intraclass correlations and smallest detectable differences were calculated over an increasing number of consecutive days from week 1. Reliability was good to excellent when whole weeks were assessed. Our results indicate that a minimum of two days of observation are required to obtain an ICC ≥ 0.7 for most activities, except for lying and median duration of locomotion bouts, which required up to five days.
Michiel Punt, Sjoerd M. Bruijn, Ingrid G. van de Port, Ilona J.M. de Rooij, Harriet Wittink and Jaap H. van Dieën
A recent review indicated that perturbation-based training (PBT) interventions are effective in reducing falls in older adults and patients with Parkinson’s disease. It is unknown whether this type of intervention is effective in stroke survivors. We determined whether PBT can enhance gait stability in stroke survivors. A total of 10 chronic stroke survivors who experienced falls in the past 6 months participated in the PBT. Participants performed 10 training sessions over a 6-week period. The gait training protocol was progressive, and each training contained unexpected gait perturbations and expected gait perturbations. Evaluation of gait stability was performed by determining steady-state gait characteristics and daily-life gait characteristics. We previously developed fall prediction models for both gait assessment methods. We evaluated whether predicted fall risk was reduced after PBT according to both models. Steady-state gait characteristics significantly improved, and consequently, predicted fall risk was reduced after the PBT. However, daily-life gait characteristics did not change, and thus, predicted fall risk based on daily-life gait remained unchanged after the PBT. A PBT resulted in more stable gait on a treadmill and thus lower predicted fall risk. However, the more stable gait on the treadmill did not transfer to a more stable gait in daily life.