Lynsey D. Duffell

Long-term intensive electrically stimulated cycling by spinal cord-injured people: effect on muscle properties and their relation to power output.

Inactivity and muscular adaptations following spinal cord injury (SCI) result in secondary complications such as cardiovascular disease, obesity, and pressure sores. Functional electrically stimulated (FES) cycling can potentially reduce these complications, but previous studies have provided inconsistent results. We studied the effect of intensive long‐term FES cycle training on muscle properties in 11 SCI subjects (mean ± SEM: 41.8 ± 2.3 years) who had trained for up to 1 hour/day, 5 days/week, for 1 year. Comparative measurements were made in 10 able‐bodied (AB) subjects. Quadriceps maximal electrically stimulated torque increased fivefold (n = 5), but remained lower than in AB individuals. Relative force response at 1 HZ decreased, relaxation rate remained unchanged, and fatigue resistance improved significantly. Power output (PO) improved to a lesser extent than quadriceps torque and not to a greater extent than has been reported previously. We need to understand the factors that limit PO in order to maximize the benefits of FES cycling. Muscle Nerve 38: 1304–1311, 2008

Balance and gait adaptations in patients with early knee osteoarthritis

Highlights • High knee adduction moments do not occur in early osteoarthritis.• People with early knee-joint osteoarthritis show impairments in balance.• Altered muscle activation is associated with early osteoarthritis during balance tasks.

Comparison of kinematic and kinetic parameters calculated using a cluster-based model and Vicon’s plug-in gait:

Gait analysis is an important clinical tool. A variety of models are used for gait analysis, each yielding different results. Errors in model outputs can occur due to inaccurate marker placement and skin motion artefacts, which may be reduced using a cluster-based model. We aimed to compare a custom-made cluster model (ClusBB) with Vicon’s plug-in gait. A total of 21 healthy subjects wore marker sets for the ClusBB and plug-in gait models simultaneously while walking on a 6-m walkway. Marker and force plate data were captured synchronously and joint angles/moments were calculated using both models. There was good correlation between the models (coefficient of multiple correlations > 0.65) and good intra-session correlation for both models (coefficient of multiple correlations > 0.80). Inter-subject variability was high, ranging from 15° to 40° in the sagittal plane and 11° to 52° in the coronal and transverse planes. Intra-subject variability was small for both ClusBB and plug-in gait models. Inter-subject variance tended to be high in both models for knee abduction/adduction, but particularly so for plug-in gait, suggesting that a cluster-based model may reduce the variability. The inter-subject variance in out-of-sagittal plane data is of particular importance clinically, given the reliance on these datasets in clinical decision-making.

Electromyographic activity of pelvic and lower limb muscles during postural tasks in people with benign joint hypermobility syndrome and non hypermobile people. A pilot study

Benign joint hypermobility syndrome (BJHS) is associated with the early development of certain degenerative conditions, which may be associated with altered muscle activity. This pilot study compared muscle activation patterns during postural tasks between people with BJHS who do not have pain and people with normal flexibility (control group). Sixteen subjects aged 22–45 years (8 with BJHS) were selected from a population recruited to a larger study. Electromyographic activity of erector spinae (ES), gluteus medius (GM), and lower limb (rectus femoris (RF), semitendinosus (ST), tibialis anterior (TA) and gastrocnemius lateralis) muscles was assessed, and chosen based on the muscles being tested in the larger study. Subjects carried out 30 s of quiet standing (QS) and one-leg standing (OLS), both with eyes open (EO) and eyes closed (EC). Both groups had significantly more TA activity, and control subjects had significantly more GM activity, during OLS EC compared with QS. GM activity was not significantly different between groups. Compared with the BJHS group, control subjects had significantly less ST activation overall, significantly more ES activity during OLS EC and significantly less RF-ST co-contraction during QS. This study has noted differences in muscle activation patterns between pain-free hypermobile people and control subjects, specifically involving muscles surrounding the pelvis and hip. This pilot data suggests that strategies for stabilising the body during balancing tasks may be relevant to injury risk in people with BJHS. While results need to be verified with a larger subject sample, this study is important in developing new treatments for hypermobile people.

Measuring body weight distribution during sit-to-stand in patients with early knee osteoarthritis

People with severe degenerative conditions, such as osteoarthritis (OA), have been shown to have altered movement patterns during sit-to-stand. However it remains unclear whether such alterations exist in people with early OA, in the absence of pain. This study aimed to determine if a novel seat could be used to discriminate people with early OA compared with controls. The sit-to-stand task was performed by 20 people with early medial knee OA and 20 age and gender-matched control subjects, using an instrumented seat. OA subjects showed altered weight distribution in the transition phase from sit to stand, in that they placed more load through their unaffected side. Task duration was significantly longer for OA subjects, and ground reaction force integrals were significantly greater for both legs of OA subjects. OA subjects had significantly higher knee flexion and adduction moments in their unaffected compared with affected side. This study has demonstrated that a novel instrumented seat can be used to discriminate people with early medial knee OA during the sit-to-stand activity. These results may be relevant for early interventions to delay or prevent changes in muscle function of the affected limb as well as contralateral knee or hip osteoarthritis in these patients.

Power Output During Functional Electrically Stimulated Cycling in Trained Spinal Cord Injured People

Objectives. This study is to compare relationships between muscle size, strength, and power output (PO) in trained spinal cord injured (SCI) people and able‐bodied (AB) people; and to compare methodologies for measuring PO during functional electrically stimulated (FES) cycling. Subjects. Trained SCI people (N= 5) and five AB subjects of similar physical characteristics. Materials and Methods. Thickness and strength of the quadriceps muscles and PO during 1) incremental exercise test (IET); 2) maximal stimulation test (MST) in SCI people and during an explosive exercise test in AB subjects. Results. In SCI people, muscle thickness, strength, and peak PO reached 88, 34, and 13% of AB, respectively. Steady state PO (MST) was similar to maximal PO (IET). Conclusions. Peak PO was lower than expected in trained SCI people. Muscle recruitment and efficiency during FES cycling require optimization to improve PO. An MST is a more convenient and informative measure of PO during FES cycling.

Knee moments of anterior cruciate ligament reconstructed and control participants during normal and inclined walking

Objectives Prior injury to the knee, particularly anterior cruciate ligament (ACL) injury, is known to predispose one to premature osteoarthritis (OA). The study sought to explore if there was a biomechanical rationale for this process by investigating changes in external knee moments between people with a history of ACL injury and uninjured participants during walking: (1) on different surface inclines and (2) at different speeds. In addition we assessed functional differences between the groups. Participants 12 participants who had undergone ACL reconstruction (ACLR) and 12 volunteers with no history of knee trauma or injury were recruited into this study. Peak knee flexion and adduction moments were assessed during flat (normal and slow speed), uphill and downhill walking using an inclined walkway with an embedded Kistler Force plate, and a ten-camera Vicon motion capture system. Knee injury and Osteoarthritis Outcome Score (KOOS) was used to assess function. Multivariate analysis of variance (MANOVA) was used to examine statistical differences in gait and KOOS outcomes. Results No significant difference was observed in the peak knee adduction moment between ACLR and control participants, however, in further analysis, MANOVA revealed that ACLR participants with an additional meniscal tear or collateral ligament damage (7 participants) had a significantly higher adduction moment (0.33±0.12 Nm/kg m) when compared with those with isolated ACLR (5 participants, 0.1±0.057 Nm/kg m) during gait at their normal speed (p<0.05). A similar (non-significant) trend was seen during slow, uphill and downhill gait. Conclusions Participants with an isolated ACLR had a reduced adductor moment rather an increased moment, thus questioning prior theories on OA development. In contrast, those participants who had sustained associated trauma to other key knee structures were observed to have an increased adduction moment. Additional injury concurrent with an ACL rupture may lead to a higher predisposition to osteoarthritis than isolated ACL deficiency alone.

Frequency analysis of wireless accelerometer and EMG sensors data: Towards discrimination of normal and asymmetric walking pattern

This preliminary study reports on the combined use of wireless accelerometers and wireless EMG sensors for monitoring walking patterns. The sensor data was analyzed in frequency domain through FFT, PSD and time-frequency spectrogram analysis. Accelerometer spectra was found to shift towards lower frequencies (<;3 Hz) while EMG spectra of selected muscles shifted towards higher frequencies (>;50 Hz) during asymmetric walking. Median frequency was used to quantify the spectral shifts. The combined wireless accelerometer/EMG system showed potential for discrimination between the normal and asymmetric walking.

The Complexity of Human Walking: A Knee Osteoarthritis Study

This study proposes a framework for deconstructing complex walking patterns to create a simple principal component space before checking whether the projection to this space is suitable for identifying changes from the normality. We focus on knee osteoarthritis, the most common knee joint disease and the second leading cause of disability. Knee osteoarthritis affects over 250 million people worldwide. The motivation for projecting the highly dimensional movements to a lower dimensional and simpler space is our belief that motor behaviour can be understood by identifying a simplicity via projection to a low principal component space, which may reflect upon the underlying mechanism. To study this, we recruited 180 subjects, 47 of which reported that they had knee osteoarthritis. They were asked to walk several times along a walkway equipped with two force plates that capture their ground reaction forces along 3 axes, namely vertical, anterior-posterior, and medio-lateral, at 1000 Hz. Data when the subject does not clearly strike the force plate were excluded, leaving 1–3 gait cycles per subject. To examine the complexity of human walking, we applied dimensionality reduction via Probabilistic Principal Component Analysis. The first principal component explains 34% of the variance in the data, whereas over 80% of the variance is explained by 8 principal components or more. This proves the complexity of the underlying structure of the ground reaction forces. To examine if our musculoskeletal system generates movements that are distinguishable between normal and pathological subjects in a low dimensional principal component space, we applied a Bayes classifier. For the tested cross-validated, subject-independent experimental protocol, the classification accuracy equals 82.62%. Also, a novel complexity measure is proposed, which can be used as an objective index to facilitate clinical decision making. This measure proves that knee osteoarthritis subjects exhibit more variability in the two-dimensional principal component space.

The knee adduction angle of the osteo-arthritic knee: a comparison of 3D supine, static and dynamic alignment.

BACKGROUND End-stage knee osteoarthritis (OA) commonly results in knee arthroplasty. Three dimensional (3D) supine imaging is often used for pre-operative planning to optimise post-operative knee adduction angles (KAA). However, supine imaging may not represent loaded knee alignment. The aim of this study was to investigate differences in knee alignment under supine, static and dynamic conditions in healthy subjects and subjects with knee OA. METHODS Nine healthy subjects and 15 subjects with end-stage knee OA were recruited. All subjects underwent supine imaging and motion capture during gait. KAAs were calculated from supine images (SUPINE), upright standing (STATIC) and at the first peak ground reaction force during gait (DYNAMIC), and were compared. RESULTS KAAs were significantly higher (more varus) during gait compared with static (loaded and unloaded) in healthy subjects (p<0.01) but not in subjects with knee OA. There was a good correlation between SUPINE and DYNAMIC for both healthy and OA subjects (R(2)>0.58), with differences in the two relationships; healthy knees had a higher KAA during gait for any given KAA in the supine position, whereas OA knees that were valgus in imaging became more valgus during gait, and the opposite occurred for varus knees. CONCLUSIONS Factors that may contribute to the noted differences between healthy and OA subjects include morphological changes in the joint as a result of OA, and gait compensation strategies in people with end-stage OA. Dynamic 3D motion capture provides important information about functional alignment that is not provided by supine imaging or static motion capture. CLINICAL RELEVANCE Gait analysis may provide useful information to the surgeon during surgical planning of knee arthroplasties.