The relationships between physical capacity and biomechanical plasticity in old adults during level and incline walking

Advanced Age Redistributes Positive but Not Negative Leg Joint Work during Walking

“…In addition, even when walking at the same speed as young adults, older adults produce 16%–30% less positive plantarflexor work and 22%–82% more positive hip flexor and extensor work (4,8). This age-related distal-to-proximal redistribution in positive leg joint work is a robust phenomenon, evident at various walking speeds (8,9), surface inclines (10), and physical activity histories (11) and in older adults of various physical capacities (12). It is also functionally relevant; reduced plantarflexor work correlates with slower walking speeds (13), and a reliance on positive work performed by the hip musculature can worsen walking economy (14).…”

Lower extremity joints and muscle groups in the human locomotor system alter mechanical functions to meet task demand

“…Fourth, although this analysis quantifies mechanical function at each joint and muscle group, it does not take into account the amount of work performed at each joint or by each muscle group. For example, although we provide evidence that all three joints become more motor-like during uphill walking, total positive work is disproportionately increased at the hip compared with the knee or ankle during uphill walking (Alexander et al, 2017;Franz and Kram, 2014;Kuhman et al, 2018b;Lay et al, 2006). This suggests that, although all three joints and their extensors act more like motors during uphill walking, humans prefer to distribute most of the added work incurred from the task to a specific joint or muscle group (in the case of uphill walking, the hip extensors).…”

“…There is strong evidence that humans utilize central mechanical flexibility during locomotion. To walk uphill, humans disproportionately increase mechanical output from the hip extensors; to walk downhill, they disproportionately increase mechanical output from the knee extensors; running compared with walking at the same speed (2.0 m s −1 ) involves a disproportionate increase in mechanical output from the ankle extensors (Alexander et al, 2017;Farris and Sawicki, 2012;Franz and Kram, 2014;Kuhman et al, 2018b;Lay et al, 2006;Pickle et al, 2016;Sawicki et al, 2009). These findings indicate that humans regularly rely on central mechanical flexibility during locomotion.…”

“…speed, energetic cost, dynamic stability) in general. For example, advanced age is associated with decreased mechanical output from the ankle extensors and increased mechanical output from the hip extensors and/or flexors (DeVita and Hortobagyi, 2000;Franz and Kram, 2014;Kuhman et al, 2018b;Silder et al, 2008). Furthermore, the magnitude of this distal-to-proximal shift in joint-level mechanical output is larger during maximal compared with comfortable speed walking and during uphill compared with level-ground walking (Kuhman et al, 2018a,b;Waanders et al, 2018).…”

“…loss of muscle strength, sub-tendon coupling in the Achilles) decrease the local flexibility of this muscle group, rendering it unable to 'adapt' to changing external demands and necessitating a central shift from the ankle to the hip (Franz andThelen, 2015, 2016). It is unclear whether this mechanical redistribution with age is beneficial or detrimental for locomotor capacity, however some flexibility is likely better than none (Franz, 2016;Kuhman et al, 2018b). A worst-case scenario would be loss of both local and central mechanical flexibility, which would render an individual unable to adapt to environmental demands.…”