Optimizing Ankle Exoskeleton Assistance for Walking Across the Life Span
Optimizing Ankle Exoskeleton Assistance for Walking Across the Life Span
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.
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. The leg tendons of older adults are more compliant than that of young
 adults. Accordingly, older adult leg tendons stretch more as under a given loaded, during
 walking and running, causing their muscles to operate at shorter 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 stiffness 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.
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 ACSM'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 unusual shortness of breath with usual activities

 -  Are <18 or 46-64 years of age

 -  Do not speak or understand English