Short communicationUnexpected walking perturbations: Reliability and validity of a new treadmill protocol to provoke muscular reflex activities at lower extremities and the trunk
Introduction
Experimentally induced stumbling during locomotion is often used to investigate kinematic and neuromuscular activation patterns in response to disturbances of dynamic postural control (Forner Cordero et al., 2003, Marigold and Misiaszek, 2009, Savin et al., 2010). Though perturbations are induced in a variety of ways, computer controlled treadmills offer the potential to generate standardized walking perturbations, which are particularly rapid and powerful (Berger et al., 1984, Forner Cordero et al., 2003, Granacher et al., 2006, Horstmann et al., 1987, Sessoms et al., 2014, Sloot et al., 2015). Such characteristics are specifically required for investigations in muscular reflex activities following the perturbation (Granacher et al., 2006, Müller et al., 2016, Sloot et al., 2015). For valid identification of reflex activities, discriminated from ongoing perturbation effects, the application of short timed stimuli is crucial (Sloot et al., 2015). Also, as neuromuscular responses and recovery strategies are related to the specific gait phase, a distinct timing of stimuli application is inevitable (Forner Cordero et al., 2003, Schillings et al., 2000). Though meeting these requirements is technically challenging, data on reliability and validity of applied perturbation characteristics during perturbed treadmill walking are rare (Horstmann et al., 1987, Sessoms et al., 2014, Sloot et al., 2015). In a recently published pilot investigation the authors were able to provoke neuromuscular reflex activities and kinematic changes in perturbed treadmill walking (Müller et al., 2016). While the induced perturbations lead to both a displacement of the body and to an increase of muscle EMG activity, the reliability and validity of the underlying perturbation protocol remained unknown. Therefore, the present study aimed to evaluate the technical reliability and validity of the underlying treadmill perturbation protocol, designed to specifically provoke muscular reflex responses at the trunk and lower extremities.
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Participants
Fourteen participants (6 females, 8 males; 27 ± 3 years, 76 ± 13 kg, 1.79 ± 0.10 m) underwent a treadmill walking protocol in a test re-test design (two weeks in between). Participants met the following inclusion criteria: (1) physically active at least two times per week, (2) age: 18–50 years, (3) no pain/discomfort at the musculoskeletal system at the time point of the study participation. A clinical investigation by a physician ruled out underlying pathologies at the trunk and lower extremities. All
Reliability and validity of perturbation characteristics
TRV for perturbation delay, duration and amplitude ranged from 5.0% to 5.7%. LoA reached 3 ± 36 ms for delay, 2 ± 13 ms for duration and 0.0 ± 0.3 m/s for amplitude (Table 1). Differences between targeted and observed velocity alterations reached 2 ms for delay, 2 ms for stimulus duration and 0.1 m/s for amplitudes.
Amplitudes and latencies of muscular reflex responses
EMG amplitudes following perturbations ranged between 106 ± 97% (left GM) and 909 ± 979% (right RA) of unperturbed gait (Table 2). EMG latencies ranged between 82 ± 14 ms (left ESL) and 106 ± 16 ms (right
Discussion
This study investigated the test-retest reliability and validity of a new treadmill perturbation protocol, which releases rapid and unexpected belt perturbations to provoke muscular reflex responses at lower extremities and the trunk. Comparison of pre-set and observed perturbations revealed excellent accuracy of stimuli characteristics with minor differences of up to 5% for timing, amplitude and duration. Test-retest results showed a high reliability of the protocol, indicated by a TRV <6% and
Conflict of interest
There are no conflicts of interest.
Acknowledgements
The present study was initiated and funded by the German Federal Institute of Sport Science and realized within MiSpEx – the National Research Network for Medicine in Spine Exercise (granted number: BISp IIA1-080102A/11-14).
The present study was funded by the European Union (ERDF – European Regional Development Fund).
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