Author(s): BENÍTEZ FLORES, S., FERRARO FARRO, D., TRUJILLO BAAMEIRO, D., PÉREZ CASTILLA, A., DE SOUZA CASTRO, F.A., Institution: UNIVERSIDAD DE LA REPÚBLICA , Country: URUGUAY, Abstract-ID: 1763

INTRODUCTION:
Strength is essential for both health and athletic performance. The rate of force development (RFD), defined as the slope of the force–time curve during maximal voluntary contraction, is closely related to sport performance and daily functional capacity. However, traditional dynamometers are expensive and limited to single-joint assessments, reducing their field applicability. Therefore, this study aims to evaluate the concurrent reliability of a novel, low-cost functional dynamometer for multi-joint movements.
METHODS:
Twenty male participants (age: 29.4 ± 6.7 years; body mass index: 25.6 ± 2.4 kg·m⁻²) with at least two years of strength training experience took part in this study. On day one, participants were familiarized with four isometric exercises (Biceps Curl, Mid-Thigh Pull, Row, and Leg Extension). Seven days later, they performed three maximal trials per exercise with two minutes of rest between attempts. Force was recorded simultaneously using two dynamometers connected in series: a validated DynaSystem (DS) (SYMOTECH, Granada, Spain) sampling at 1000 Hz and the Valkyria Trainer (VT) (IVOLUTION, Santa Fe, Argentina) sampling at 80 Hz. Data are presented as mean ± SD and 95% CI. The CV and ICC were calculated to assess inter-trial and inter-device reliability. Also, a two-way factorial ANOVA (3 [Trials] × 2 [Equipments]) was performed. For brevity, only the Mid-Thigh Pull and Row results are reported.
RESULTS:
Peak force was similar in Mid-Thigh Pull (VT 1325±244 N, CV 18%, CI 1180-1451 N; DynaSystem 1323±237 N, CV 18%, CI 1179-1456 N, ANOVA effects p>0.05, ICC=0.98, p<0.001). Peak force was similar in Row (VT 656±167 N, CV 25%, CI 568-748 N; DS 579±145 N, CV 25%, CI 501-661 N, ANOVA effects p>0.05, ICC=0.98, p<0.001). Regarding RFD at 250 ms was different in Mid-Thigh Pull (VT 2907±1235 N·s⁻1, CV 42%, CI 2165-3694 N·s⁻1; DS 4251±845 N·s⁻1, CV 20%, CI 3627-4815 N·s⁻1, ANOVA device effect p<0.5, with ICC=0.56, p<0.039). Regarding RFD at 250 ms was different in Row (VT 1206±965 N·s⁻1, CV 80%, CI 769-1809 N·s⁻1; DS 1990±645 N·s⁻1, CV 32%, CI 1634-2303 N·s⁻1, ANOVA device effect p<0.5, with ICC=0.84, p<0.001).
CONCLUSION:
The VT is reliable to measure peak force but shows systematic error for RFD.

References
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