Stanford Advisors


All Publications


  • Changes in stair ascent biomechanics two to eight years after ACL reconstruction are associated with patient-reported outcomes GAIT & POSTURE Fischer, A. G., Erhart-Hledik, J. C., Chu, C. R., Asay, J. L., Andriacchi, T. P. 2019; 69: 91–95
  • Activating the somatosensory system enhances net quadriceps moment during gait. Journal of biomechanics Fischer, A. G., Erhart-Hledik, J. C., Asay, J. L., Chu, C. R., Andriacchi, T. P. 2018

    Abstract

    Quadriceps muscle rehabilitation following knee injury or disease is often hampered by pain, proprioception deficits or instability associated with inhibition of quadriceps activation during walking. The cross-modal plasticity of the somatosensory system with common sensory pathways including pain, pressure and vibration offers a novel opportunity to enhance quadriceps function during walking. This study explores the effectiveness of an active knee brace that used intermittent cutaneous vibration during walking to enhance the peak knee flexion moment (KFM) during early stance phase as a surrogate for net quadriceps moment (balance between knee extensor and flexor muscle moments). The stimulus was turned on prior to heel strike and turned off at mid-stance of the gait cycle. Twenty-one subjects with knee pathologies known to inhibit quadriceps function were tested walking under three conditions: control (no brace), a passive brace, and an active brace. Findings show that compared to the control, subjects wearing an active brace during gait exhibited a significant (p < 0.001) increase in peak KFM and no significant difference when wearing a passive brace (p = 0.17). Furthermore, subjects with low KFM and knee flexion angle (KFA) in control exhibited the greatest increase in KFA at loading response in the active brace condition (R = 0.47, p < 0.05). Intermittent cutaneous stimulation during gait, therefore, provides an efficient method for increasing the KFM in patients with knee pathologies. This study's results suggest that intermittent vibration stimulus can activate the cross-modalities of the somatosensory system in a manner that gates pain stimulus and possibly restores quadriceps function in patients with knee pain.

    View details for PubMedID 30381155

  • Effect of lateral wedge length on ambulatory knee kinetics. Gait & posture Fischer, A. G., Ulrich, B., Hoffmann, L., Jolles, B. M., Favre, J. 2018; 63: 114–18

    Abstract

    BACKGROUND: Lateral wedge insoles (LWI) were proposed to treat medial knee osteoarthritis through reductions of the ambulatory knee adduction moment (KAM). Limited attention was however paid to the LWI length, resulting in unclear understanding of its effect on KAM reductions. The knee flexion moment (KFM) was also shown to be important in knee osteoarthritis, but little is known about the effect of LWI length on it.RESEARCH QUESTION: This study aimed to compare the KAM and KFM of healthy subjects walking with four different lengths of LWI, explicitly without LWI and with LWI below the hindfoot (HF), below the hindfoot and forefoot (HF + FF) and below the hindfoot, forefoot and hallux (HF + FF + HX) segments.METHODS: Nineteen healthy participants (63% male; 24 ± 3 years old) walked in an instrumented gait lab with LWI of four different lengths. Repeated one-way ANOVAs and post-hoc t-tests were used to compare knee kinetics among LWI lengths.RESULTS: The peak value of the KAM during the first half of stance and the KAM impulse differed with respect to the LWI length (p < 0.001). A length of at least HF + FF, but not necessarily longer, was needed to decrease both KAM parameters compared to walking without LWI. The LWI length had no effect on the peak value of the KFM during the first half of stance (p = 0.86).SIGNIFICANCE: The results in this study could contribute to better selections of LWI for medial knee osteoarthritis and suggested that the length of the LWI could be a critical factor that should be considered in future research.

    View details for PubMedID 29729613

  • y The effects of body weight unloading on kinetics and muscle activity of overweight males during Overground walking CLINICAL BIOMECHANICS Fischer, A. G., Wolf, A. 2018; 52: 80–85

    Abstract

    Excess body weight has become a major worldwide health and social epidemic. Training with body weight unloading, is a common method for gait corrections for various neuromuscular impairments. In the present study we assessed the effects of body weight unloading on knee and ankle kinetics and muscle activation of overweight subjects walking overground under various levels of body weight unloading.Ten overweight subjects (25 ≤ BMI < 29.9 kg/m2) walked overground under a control and three (0%, 15%, 30%) body weight unloading experimental conditions. Gait parameters assessed under these conditions included knee and ankle flexion moments and the Electromygraphic activity of the Tibialis Anterior, Lateral Gastrocnemius and Vastus Lateralis.Increasing body weight unloading levels from 0% to 30% was found to significantly reduce the peak knee flexion and ankle plantarflexion moments. Also observed was a significant reduction in muscle activity of the Tibialis Anterior, Lateral Gastrocnemius and Vastus Lateralis under the three body-weight unloading conditions.Our results demonstrate that a reduction of up to 30% overweight subjects' body weight during gait is conducive to a reduction in the knee and ankle flexion moments and in the balancing net quadriceps moment and ankle flexors moment. The newly devised body weight unloading device is therefore an effective method for reducing joint loads allowing overweight people who require controlled weight bearing scenarios to retrain their gait while engaging in sustained walking exercise.

    View details for DOI 10.1016/j.clinbiomech.2018.01.013

    View details for Web of Science ID 000428010100013

    View details for PubMedID 29407862

  • Body weight unloading modifications on frontal plane joint moments, impulses and Center of Pressure during overground gait CLINICAL BIOMECHANICS Fischer, A. G., Wolf, A. 2016; 39: 77–83

    Abstract

    Body weight unloading is a common method of gait rehabilitation. However, little is known about its effects on the overground gait biomechanical parameters which were often confounded by the walking modality (treadmill) or the speed variability when subjects walked overground while having to pull the body weight unloading system to which they were attached. By designing a mechanical device that pulled the system at a constant speed, we were able to assess the unique effects of body weight unloading on healthy subjects' kinetics during overground gait.Fifteen healthy subjects walked overground under three (0%, 15%, and 30%) body weight unloading experimental conditions. Kinetic measures included hip and knee frontal plane moments and impulses and the foot center of pressure.A significant inverse relationship was shown between increased body weight unloading levels (0% to 30%) and a decrease in the hip and knee first adduction moments and impulses and an increase in the lateral shift of the foot center of pressure. Frontal plane hip and knee kinetic curvature patterns remained similar as evidenced by low normalized RMSE under paired comparisons of the experimental conditions.Overground gait with up to 30% body weight unloading stands out as an efficient method of reducing loads on joints without distorting kinetic gait curvature patterns. The relationship between increased unloading with decreased hip and knee moments and impulses and increased lateral shift of the center of pressure also suggests that this shift may be an important diagnostic tool in gait assessment and correction.

    View details for DOI 10.1016/j.clinbiomech.2016.09.005

    View details for Web of Science ID 000387834800012

    View details for PubMedID 27697627

  • Effects of body weight unloading on electromyographic activity during overground walking JOURNAL OF ELECTROMYOGRAPHY AND KINESIOLOGY Fischer, A. G., Debbi, E. M., Wolf, A. 2015; 25 (4): 709–14

    Abstract

    Body weight unloading (BWU) on treadmills is a common method of gait rehabilitation. However, treadmills slightly but significantly modify gait biomechanical parameters thus confound the effects of BWU. By conducting our experiments under conditions that replicate daily walking and controlling for speed variability, with a mechanical device designed to pull the BWU system at a constant speed, this study could assess the unique effects of BWU on gait electromyography (EMG) of healthy subjects.Fifteen healthy subjects walked overground in a control (no suspension vest) and three (0%, 15%, 30%) BWU experimental conditions. The EMG activity of the Tibialis Anterior (TA), Lateral Gastrocnemius (LG), Vastus Lateralis (VL), and Rectus Femoris (RF) were recorded (six trials per condition).ANOVA showed significant differences in the peak activity and integrated EMG of the TA, LG and VL. Pairwise comparisons of EMG parameters under 0% vs. 15% and 15% vs. 30% BWU levels showed that the increase in BWU levels decreased the peak and integrated EMG of the TA, LG, and VL without pattern modification.Overground gait with up to 30% BWU reduces joint loads without modifying the muscle activation patterns. Several clinical applications for overground gait reeducation with BWU are suggested.

    View details for DOI 10.1016/j.jelekin.2015.05.001

    View details for Web of Science ID 000360097400019

    View details for PubMedID 26025610

  • Assessment of the effects of body weight unloading on overground gait biomechanical parameters CLINICAL BIOMECHANICS Fischer, A. G., Wolf, A. 2015; 30 (5): 454–61

    Abstract

    Gait rehabilitation with body weight unloading is a common method of gait rehabilitation for clinical subjects with neurological and musculoskeletal impairments. However, the efficiency of this method was hard to assess given the confounding variables walking modality (treadmill vs. overground) and subjects' inability to maintain a comfortable speed when pulling a body weight unloading system by which they were suspended. By controlling the gait modality (overground) and devising a mechanical device that pulled the system at a constant speed, this study could examine the unique effects of body weight unloading on the biomechanical parameters of healthy subjects walking overground at comfortable speed.Ten healthy subjects were instructed to walk overground under a control (no suspension vest) and three (0%, 15%, 30%) body weight unloading experimental conditions. Hip, knee and ankle spatiotemporal, kinematic, and kinetic measures were recorded for all conditions (six trials per condition).ANOVA showed no changes in cadence, speed and stride length, a reduction in double limb support and increase in single limb support. Pairwise comparisons of gait parameters under 0%,15% and 30% body weight unloading conditions indicated significant reductions in lower joint kinematics and kinetics with increased body weight unloading. Additionally, despite changes in the peak values of kinematic and kinetic measures, the curvature patterns remained unchanged.This study shows that overground gait with up to 30% body weight unloading reduces joint loads without modifying gait curvature patterns or the plantarflexion angle. Several clinical applications for gait reeducation conducted in situ with unloading are enumerated.

    View details for DOI 10.1016/j.clinbiomech.2015.03.010

    View details for Web of Science ID 000355365900010

    View details for PubMedID 25798857

  • KNEE KINEMATIC AND KINETIC MODIFICATIONS UNDER BODY WEIGHT UNLOADING DURING OVERGROUND WALKING AT A CONSTANT SPEED Fischer, A. G., Debbi, E. M., Wolf, A. ELSEVIER SCI LTD. 2013: S101–S102