Are Age, Self-Selected Walking Speed, or Propulsion Force Predictors of Gait-Related Changes in Older Adults?

There is limited research that directly compares the effect of reduced speed with reduced propulsive force production (PFP) on age-related gait changes. We aimed to determine how changes in the gait of older adults correlate with age, speed, or peak PFP over a 6-year span. We collected kinematics and kinetics of 17 older subjects at 2 time points. We determined which biomechanical variables changed significantly between visits and used linear regressions to determine whether combinations of self-selected walking speed, peak PFP, and age correlated to changes in these variables. We found a suite of gait-related changes that occurred in the 6-year period, in line with previous aging studies. Of the 10 significant changes, we found 2 with significant regressions. Self-selected walking speed was a significant indicator of step length, not peak PFP or age. Peak PFP was a significant indicator for knee flexion. None of the biomechanical changes were correlated to the chronological age of the subjects. Few gait parameters had a correlation to the independent variables, suggesting that changes in gait mechanics were not solely correlated to peak PFP, speed, and/or age. This study improves understanding of changes in ambulation that lead to age-related gait modifications.

Comparison of Knee Kinematics and Kinetics during Stair Descent in Single- and Multi-Radius Total Knee Arthroplasty.

Despite continuing advances, nearly 20% of patients remain dissatisfied with their total knee arthroplasty (TKA) outcomes. Single-radius (SR) and multiradius (MR) TKA designs are two commonly used knee replacement designs based on competing theories of the flexion/extension axis of the knee. Our aim was to characterize stair descent kinematics and kinetics in SR and MR TKA subjects. We hypothesized that 1 year after TKA, patients who received SR TKA will more closely replicate the knee kinematics and kinetics of healthy age-matched controls during stair descent, than will MR TKA patients. SR subjects (n = 12), MR subjects (n = 12), and age-matched controls (n = 12) descended four stairs affixed to force platforms, while 10 infrared cameras tracked markers attached to the body to collect kinematic and kinetic data. Both patient groups had improvements in stair descent kinetics and kinematics at the 1-year postoperative time point. However, SR TKA subjects were indistinguishable statistically from age-matched controls, while MR TKA subjects retained many differences from controls. Similar to previous reports for level walking, the SR knee design performs closer to healthy controls than MR knees during stair descent. This study demonstrates that patients who receive SR TKA have more improved kinematic normalization during stair descent postoperatively than those who received an MR TKA.

Comparison of Knee Kinematics and Kinetics during Stair Ascent in Single-Radius and Multiradius Total Knee Arthroplasty.

Traditionally total knee arthroplasty (TKA) design has been based on theories of the movement of the healthy knee joint. Currently, there are two competing theories on the flexion/extension axis of rotation of the knee with disparate radii of rotation, and thus differing movement patterns. The purpose of our study was to compare stair ascent kinematics and kinetics of single-radius (SR) and multiradius (MR) TKA subjects. We hypothesized that the knee kinematics and kinetics of SR TKA patients would more closely replicate healthy age matched controls during stair ascent than MR TKA patients, 1 year after TKA. Both patient groups had large improvements in biomechanical and clinical outcome measures following surgical intervention. However, the SR knee design performs closer to healthy controls than MR knees during stair ascent, supporting results that have been previously obtained for level walking. SR TKA subjects demonstrated reduced power production and sagittal moment compared with controls, albeit more than MR TKA subjects. This study demonstrates that patients who receive SR TKA have kinematics more closely aligned to normal patterns postoperatively than those who received an MR TKA. The power production and sagittal moment of the healthy controls most closely match previously published values of younger adults, SR TKA group most closely matches older adults, while the MR TKA group has lower power production and sagittal moments than either previously published age group. This strongly suggests that the biomechanical differences found in this study are evidence of functional deficiencies. Further research is needed to determine how these deficiencies progress with patient aging.

Muscle contributions to propulsion and braking during walking and running: insight from external force perturbations.

There remains substantial debate as to the specific contributions of individual muscles to center of mass accelerations during walking and running. To gain insight, we altered the demand for muscular propulsion and braking by applying external horizontal impeding and aiding forces near the center of mass as subjects walked and ran on a treadmill. We recorded electromyographic activity of the gluteus maximus (superior and inferior portions), the gluteus medius, biceps femoris, semitendinosus/membrinosus, vastus medialis, lateral and medial gastrocnemius and soleus. We reasoned that activity in a propulsive muscle would increase with external impeding force and decrease with external aiding force whereas activity in a braking muscle would show the opposite. We found that during walking the gastrocnemius and gluteus maximus provide propulsion while the vasti are central in providing braking. During running, we found that the gluteus maximus, vastus medialis, gastrocnemius and soleus all contribute to propulsion.

Activity and functions of the human gluteal muscles in walking, running, sprinting, and climbing.

It has been suggested that the uniquely large gluteus maximus (GMAX) muscles were an important adaptation during hominin evolution based on numerous anatomical differences between humans and extant apes. GMAX electromyographic (EMG) signals have been quantified for numerous individual movements, but not across the range of locomotor gaits and speeds for the same subjects. Thus, comparing relative EMG amplitudes between these activities has not been possible. We assessed the EMG activity of the gluteal muscles during walking, running, sprinting, and climbing. To gain further insight into the function of the gluteal muscles during locomotion, we measured muscle activity during walking and running with external devices that increased or decreased the need to control either forward or backward trunk pitch. We hypothesized that 1) GMAX EMG activity would be greatest during sprinting and climbing and 2) GMAX EMG activity would be modulated in response to altered forward trunk pitch demands during running. We found that GMAX activity in running was greater than walking and similar to climbing. However, the activity during sprinting was much greater than during running. Further, only the inferior portion of the GMAX had a significant change with altered trunk pitch demands, suggesting that the hip extensors have a limited contribution to the control of trunk pitch movements during running. Overall, our data suggest that the large size of the GMAX reflects its multifaceted role during rapid and powerful movements rather than as a specific adaptation for a single submaximal task such as endurance running.