Optimizing Ankle Exoskeleton Assistance for Walking Across the Life Span

Study Overview
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Brief Summary
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The investigators seek to 1) determine why older adults expend more metabolic energy during walking than young adults, and 2) reduce the older adult's metabolic energy expenditure during walking using an ankle exoskeleton.

Detailed Description
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Older adults walk with greater metabolic rates than young adults. Growing evidence suggests that the greater older adult metabolic rates are related to the structural properties of their lower leg tissues. The tendons of the leg of older adults are more compliant than that of young adults. Accordingly, older adult leg tendons stretch more under a given load, such as walking and running, causing their muscles to operate at shorter, less optimal lengths, and higher activations than that of young adults. Using shorter muscles lengths and more muscle activation offers less economical force production. Thus, the investigators seek to alter the passive stiffness acting about the ankle, using an ankle exoskeleton in-parallel to the ankle, thereby enabling muscles to operate at relatively longer lengths. Generally, muscles produce force more economically when they are at operating lengths greater than that exhibited during normal walking. By adding an exoskeleton in-parallel to the ankle, the investigators hypothesize that older adults will walk with longer plantar flexor muscle lengths, thereby lessening their muscle activation, and consequently, reducing whole-body metabolic rate during walking. In this study, the investigators will have young and older adults perform isolated calf muscle contractions while the investigators capture the behavior of their leg muscles and tendons using a non-invasive ultrasound probe that sits flush to the participant's skin. The investigators will also have participants walk on a treadmill with the ankle exoskeleton set at multiple assistance values. During these trials, the investigators will take many physiological and biomechanical measurements to assess why the optimal ankle exoskeleton profile minimizes the metabolic cost of walking in young and older adults.

Official Title
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Optimizing Ankle Exoskeleton Assistance for Walking Across the Life Span

Conditions
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Aging

Intervention / Treatment
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* Device: Strengthening muscle contractions during walking


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Subjects must be able to walk for 60 minutes in a 90-minute time frame. Subjects are apparently free of cardiovascular, metabolic, and renal disease, which includes no signs or symptoms suggestive of cardiovascular, metabolic or renal disease. Subjects have no current musculoskeletal injury. Subjects need to be either 18-45 or 65+ years old. These criteria meet the American College of Sports Medicine's 2015 guidelines for participant health screening prior to joining a moderate or moderate-to-vigorous exercise protocol. (Riebe et al., 2015). Exclusion Criteria: Have dementia or an inability to give informed consent Have a musculoskeletal injury or feel pain while walking Have a history of dizziness and/or balance problems Have cardiovascular, heart, metabolic, or renal disease, or respiratory problems Smoke cigarettes Asthma Feel pain or discomfort in the chest, neck, jaw, arms during rest or exercise Have orthopnea or paroxysmal nocturnal dyspnea Have ankle edema Have palpitations or tachycardia Have a heart murmur Have had a heart attack Have diabetes Have a pace maker Have unusual shortness of breath with usual activities Are <18 or 46-64 years of age Do not speak or understand English

Ages Eligible for Study
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Minimum Age: 18 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Basic Science
Intervention Model: Single Group Assignment
Interventional Model Description: All participants will perform the same trials/sessions to complete the entire protocol. After each participant has performed all trials for this study, the investigators will analyze the data of this repeated-measures design.
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Economical muscle dynamics<br>The investigators are trying to figure out how to optimize muscle contractile conditions for mobility. To do this, the investigators are systematically altering muscle contraction conditions for all participants. | Device: Strengthening muscle contractions during walking<br>* The investigators will use ankle-exoskeletons to systematically alter the behavior of participant muscle contractions. For example, participants will walk in a robotic device that adds a spring in parallel with their lower limb that will help the participants generate a stronger propulsive push-off and may reduce the effort of walking.<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Metabolic rate (watts) | The rate of metabolic energy that subjects expend during walking. | 1 year | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Preferred walking speed (m/s) | Measurements will be taken on how fast subjects prefer to walk with each exoskeleton.condition | 1 year | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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Walking, Aging, Exoskeleton Device