All Publications

  • Optimizing exoskeleton assistance to improve walking speed and energy economy for older adults. Journal of neuroengineering and rehabilitation Lakmazaheri, A., Song, S., Vuong, B. B., Biskner, B., Kado, D. M., Collins, S. H. 2024; 21 (1): 1


    Walking speed and energy economy tend to decline with age. Lower-limb exoskeletons have demonstrated potential to improve either measure, but primarily in studies conducted on healthy younger adults. Promising techniques like optimization of exoskeleton assistance have yet to be tested with older populations, while speed and energy consumption have yet to be simultaneously optimized for any population.We investigated the effectiveness of human-in-the-loop optimization of ankle exoskeletons with older adults. Ten healthy adults > 65 years of age (5 females; mean age: 72 ± 3 yrs) participated in approximately 240 min of training and optimization with tethered ankle exoskeletons on a self-paced treadmill. Multi-objective human-in-the-loop optimization was used to identify assistive ankle plantarflexion torque patterns that simultaneously improved self-selected walking speed and metabolic rate. The effects of optimized exoskeleton assistance were evaluated in separate trials.Optimized exoskeleton assistance improved walking performance for older adults. Both objectives were simultaneously improved; self-selected walking speed increased by 8% (0.10 m/s; p = 0.001) and metabolic rate decreased by 19% (p = 0.007), resulting in a 25% decrease in energetic cost of transport (p = 8e-4) compared to walking with exoskeletons applying zero torque. Compared to younger participants in studies optimizing a single objective, our participants required lower exoskeleton torques, experienced smaller improvements in energy use, and required more time for motor adaptation.Our results confirm that exoskeleton assistance can improve walking performance for older adults and show that multiple objectives can be simultaneously addressed through human-in-the-loop optimization.

    View details for DOI 10.1186/s12984-023-01287-5

    View details for PubMedID 38167151

    View details for PubMedCentralID 6620279

  • Comparing optimized exoskeleton assistance of the hip, knee, and ankle in single and multi-joint configurations. Wearable technologies Franks, P. W., Bryan, G. M., Martin, R. M., Reyes, R., Lakmazaheri, A. C., Collins, S. H. 2021; 2: e16


    Exoskeletons that assist the hip, knee, and ankle joints have begun to improve human mobility, particularly by reducing the metabolic cost of walking. However, direct comparisons of optimal assistance of these joints, or their combinations, have not yet been possible. Assisting multiple joints may be more beneficial than the sum of individual effects, because muscles often span multiple joints, or less effective, because single-joint assistance can indirectly aid other joints. In this study, we used a hip-knee-ankle exoskeleton emulator paired with human-in-the-loop optimization to find single-joint, two-joint, and whole-leg assistance that maximally reduced the metabolic cost of walking. Hip-only and ankle-only assistance reduced the metabolic cost of walking by 26 and 30% relative to walking in the device unassisted, confirming that both joints are good targets for assistance (N = 3). Knee-only assistance reduced the metabolic cost of walking by 13%, demonstrating that effective knee assistance is possible (N = 3). Two-joint assistance reduced the metabolic cost of walking by between 33 and 42%, with the largest improvements coming from hip-ankle assistance (N = 3). Assisting all three joints reduced the metabolic cost of walking by 50%, showing that at least half of the metabolic energy expended during walking can be saved through exoskeleton assistance (N = 4). Changes in kinematics and muscle activity indicate that single-joint assistance indirectly assisted muscles at other joints, such that the improvement from whole-leg assistance was smaller than the sum of its single-joint parts. Exoskeletons can assist the entire limb for maximum effect, but a single well-chosen joint can be more efficient when considering additional factors such as weight and cost.

    View details for DOI 10.1017/wtc.2021.14

    View details for PubMedID 38486633

    View details for PubMedCentralID PMC10936256

  • Identity integration in people with acquired disabilities: A qualitative study JOURNAL OF PERSONALITY Adler, J. M., Lakmazaheri, A., O'Brien, E., Palmer, A., Reid, M., Tawes, E. 2021; 89 (1): 84-112


    This qualitative investigation focused on identity integration in a sample of individuals who acquired physical disabilities in adulthood. It also argues for the importance and ethics of these methods in the broader field of scholarship on personality change following adversity.Thirteen adults participated in the study. Participants engaged in an expanded Life Story Interview wherein they narrated the story of their life, including a section devoted to their story of acquiring a physical disability. In addition, participants completed questionnaires concerning their psychological well-being and maturity.We identified two dimensions of narrative themes participants used in grappling with identity integration: one represented active processing of one's life experiences and the other represented the extent to which participants described their identity as wholly transformed by the experience of acquiring a disability. When overlaid, these dimensions yielded four narrative strategies titled: Adapters, Wanderers, Drifters, and Resisters. We also observed that Adapters seemed to have better psychological well-being and maturity than the other groups.This study offers a foundation for future scholarship on identity among people with disabilities. It also describes the contexts in which retrospective, qualitative methods are especially appropriate for research on personality change following adversity.

    View details for DOI 10.1111/jopy.12533

    View details for Web of Science ID 000505616400001

    View details for PubMedID 31837271

  • Stress resilience: Narrative identity may buffer the longitudinal effects of chronic caregiving stress on mental health and telomere shortening BRAIN BEHAVIOR AND IMMUNITY Mason, A. E., Adler, J. M., Puterman, E., Lakmazaheri, A., Brucker, M., Aschbacher, K., Epel, E. S. 2019; 77: 101-109


    Chronic caregiving stress may accelerate biological aging; however, the ability to integrate the meaning of caregiving through self-awareness, adaptation, and growth can buffer the negative effects of stress. Narrative researchers have shown that people who coherently integrate difficult experiences into their life story tend to have better mental health, but no prior study has examined the prospective association between narrative identity and biological indicators, such as telomere length. We tested whether narrative identity might be prospectively associated with resilience to long-term parenting stress, depressive symptoms, and protection from telomere shortening, especially among caregivers.We conducted a semi-structured interview about parenting and quantified narrative themes by applying well-validated, standardized coding systems with high inter-rater reliability among 88 mothers: 32 "caregivers" (mothers with a child diagnosed with an autism spectrum disorder), and 56 "controls" (mothers with a neurotypical child). To assess longitudinal changes, we measured mental health (parenting stress [PS], depressive symptoms [DS]) and leukocyte telomere length [LTL], a biomarker of aging, at baseline and again 18 months later. We examined whether narrative identity themes were related to these outcomes and whether associations differed across caregivers versus controls.Caregivers exhibited significantly higher basal levels of PS and DS relative to controls (all p's < .05), but no significant difference in LTL (p > .05). Caregivers rated higher in the narrative theme of integration showed healthier future 18-month trajectories in PS (B = -0.832, 99% CI: [-1.315, -0.155], p < .01) and LTL (B = 1.193, 99% CI: [0.526, 2.130], p < .01), but no differences in depressive symptoms (p > .05), adjusting for age and antidepressant use. Analyses examining affective themes in caregiver narratives did not demonstrate significant associations. Narrative themes did not predict outcomes in controls.The data suggest that narratives reflecting coherent integration, but not necessarily affect, prospectively relate to psychological and biological stress resilience. Maternal caregivers' ability to tell an integrated story of their parenting experiences forecasts lower parenting stress and telomere shortening over time. This study suggests the possibility that helping individuals better integrate the meaning of stressful experiences, but not necessarily to affectively redeem them, may constitute a potential novel target for intervention among chronically stressed populations such as caregivers.

    View details for DOI 10.1016/j.bbi.2018.12.010

    View details for Web of Science ID 000461412600013

    View details for PubMedID 30579939

    View details for PubMedCentralID PMC6399055