Robin Gibbons

Consistency Among Musculoskeletal Models: Caveat Utilitor

Musculoskeletal simulation software and model repositories have broadened the user base able to perform musculoskeletal analysis and have facilitated in the sharing of models. As the recognition of musculoskeletal modeling continues to grow as an engineering discipline, the consistency in results derived from different models and software is becoming more critical. The purpose of this study was to compare eight models from three software packages and evaluate differences in quadriceps moment arms, predicted muscle forces, and predicted tibiofemoral contact forces for an idealized knee-extension task spanning −125 to +10° of knee extension. Substantial variation among models was observed for the majority of aspects evaluated. Differences among models were influenced by knee angle, with better agreement of moment arms and tibiofemoral joint contact force occurring at low to moderate knee flexion angles. The results suggest a lack of consistency among models and that output differences are not simply an artifact of naturally occurring inter-individual differences. Although generic musculoskeletal models can easily be scaled to consistent limb lengths and use the same muscle recruitment algorithm, the results suggest those are not sufficient conditions to produce consistent muscle or joint contact forces, even for simplified models with no potential of co-contraction.

Can FES-rowing mediate bone mineral density in SCI: a pilot study

Study design:A single case study.Objectives:To compare proximal tibia trabecular bone mineral density (BMD) of a participant with complete spinal cord injury (SCI), long-termed functional electrical stimulation-rowing (FES-R) trained, with previously reported SCI and non-SCI group norms. To estimate lower limb joint contact forces (JCFs) in the FES-R trained participant.Setting:UK University and orthopaedic hospital research centre.Methods:Bilateral proximal tibial trabecular BMD of the FES-R trained participant was measured using peripheral quantitative computerised tomography, and the data were compared with SCI and non-SCI groups. An instrumented four-channel FES-R system was used to measure the lower limb JCFs in the FES-R trained participant.Results:Structurally, proximal tibial trabecular BMD was higher in the FES-R trained participant compared with the SCI group, but was less than the non-SCI group. Furthermore, left (184.7 mg cm−3) and right (160.7 mg cm−3) BMD were well above the threshold associated with non-traumatic fracture. The knee JCFs were above the threshold known to mediate BMD in SCI, but below threshold at the hip and ankle.Conclusion:As pathological fractures predominate in the distal femur and proximal tibia in chronic SCI patients, the fact that the FES-R trained participant’s knee JCFs were above those known to partially prevent bone loss, suggests that FES-R training may provide therapeutic benefit. Although the elevated bilateral proximal tibial BMD of the FES-R participant provides circumstantial evidence of osteogenesis, this single case precludes any statement on the clinical significance. Further investigations are required involving larger numbers and additional channels of FES to increase loading at the hip and ankle.

The effect of FES-rowing training on cardiac structure and function: pilot studies in people with spinal cord injury.

Study design:Two studies were conducted: Study-1 was cross-sectional; and Study-2 a longitudinal repeated measures design.Objectives:To examine the influence of functional electrical stimulation (FES) rowing training on cardiac structure and function in people with spinal cord injury (SCI).Setting:A university sports science department and home-based FES-training.Methods:Fourteen participants with C4-T10 SCI (American Spinal Injury Association Impairment Scale A or B) were recruited for the studies. Cardiac structure and function, and peak: oxygen uptake ([Vdot ]O2peak), power output (POpeak) and heart rate (HRpeak), were compared between two FES-untrained groups (male n=3, female n=3) and an FES-trained group (male n=3) in Study-1 and longitudinally assessed in an FES-naive group (male n=1, female n=4) in Study-2. Main outcome measures left ventricular—dimensions, volumes, mass, diastolic and systolic function, and [Vdot ]O2peak, POpeak and HRpeak. In Study-2, in addition to peak values, the [Vdot ]O2 sustainable over 30 min and the related PO and HR were also assessed.Results:Sedentary participants with chronic SCI had cardiac structure and function at the lower limits of non-SCI normal ranges. Individuals with chronic SCI who habitually FES-row have cardiac structure and function that more closely resemble non-SCI populations. A programme of FES-rowing training improved cardiac structure and function in previously FES-naive people.Conclusion:FES-rowing training appears to be an effective stimulus for positive cardiac remodelling in people with SCI. Further work, with greater participant numbers, should investigate the impact of FES-rowing training on cardiac health in SCI.Sponsorship:We thank the INSPIRE Foundation, UK, for funding these studies.

FES-rowing in tetraplegia: a preliminary report.

Study design:A training intervention study using functional electrical stimulation-rowing (FES-R) in a group of eight individuals with tetraplegia.Objectives:To assess the feasibility of a structured progressive FES-R training programme in people with tetraplegia, and to explore the number and type of FES-training sessions required to enable continuous FES-R for 30 min.Setting:A fully integrated sports centre, elite rowing training centre and university sport science department.Methods:Eight participants with chronic complete and incomplete tetraplegia (C4 to C7, American Spinal Injury Association Impairment Scale A, B and C) who had not previously used any form of FES-assisted exercise, participated in the study. Participants completed a progressive FES-assisted training programme building to three continuous 30-min FES-R sessions per week at 60–80% of their predetermined peak power output. Thereafter, rowing performance was monitored for 12 months. Main outcome measures: number and type of FES-training sessions required before achieving 30-min continuous FES-R, and FES-R average power output (POav) pre and post 12 months training. Participant feedback of perceived benefits was also documented.Results:All participants were able to continuously FES-row for 30 min after completing 13±7 FES-R training sessions. Each individual POav during 30 min FES-R increased over 12 months FES-training. FES-R was found safe and well tolerated in this group of individuals with tetraplegia.Conclusion:Individuals with tetraplegia are able to engage in a progressive programme of FES-R training. Future research examining FES-R training as an adjunctive therapy in people with tetraplegia is warranted.

FES-rowing attenuates bone loss following spinal cord injury as assessed by HR-pQCT.

Neurologically motor complete spinal cord injury (SCI) presents a unique model of bone loss whereby specific regional sites are exposed to a complete loss of voluntary muscle-induced skeletal loading against gravity. This results in a high rate of bone loss, especially in the lower limbs where trabecular bone mass decreases by ~50–60% and cortical bone mass decreases by 25–34% before the rate of bone loss slows. These SCI-induced losses that are likely superimposed on continual age-related bone losses, increase the risk of low-impact fragility fracture. The fracture incidence 20 years post SCI is reported to be 4.6% per year. An intervention that effectively prevents, attenuates, or reverses bone loss is therefore highly desirable. We present a case study of an individual with chronic complete SCI, where bone loss has been attenuated following long-term functional electrical stimulation (FES)-rowing training. In this case study, we characterize the ultradistal tibia and ultradistal radius of the FES-rower with chronic complete SCI using high-resolution-peripheral quantitative computed tomography. These data are compared with a group of FES-untrained individuals with chronic complete SCI and to a normative non-SCI cohort. The evidence suggests, albeit from a single individual, that long-term FES-rowing training can attenuate bone loss secondary to chronic complete SCI. Indeed, key FES-rower’s bone metrics for the ultradistal tibia more closely resemble normative age-matched values, which may have clinical significance since the majority of fragility fractures in chronic SCI occur in the lower extremities.

Development of Functional Electrical Stimulation Rowing: The Rowstim Series

Potentially, functional electrical stimulation (FES)-assisted exercise may have an important therapeutic role in reducing comorbidities associated with spinal cord injury (SCI). Here, we present an overview of these secondary life-threatening conditions, discuss the rationale behind the development of a hybrid exercise called FES rowing, and describe our experience in developing FES rowing technology. FES rowing and sculling are unique forms of adaptive rowing for those with SCI. The paralyzed leg musculature is activated by multiple channels of electrical pulses delivered via self-adhesive electrodes attached to the skin. The stimulated muscle contractions are synchronized with voluntary rowing movements of the upper limbs. A range of steady-state FES rowing exercise intensities have been demonstrated from 15.2 ± 1.8 mL/kg/min in tetraplegia to 22.9 ±7.1 mL/kg/min in paraplegia. We expect that such high levels may help some to achieve significant reductions in the risks to their health, particularly where a dose-response relationship exists as is the case for cardiovascular disease and Type II diabetes. Furthermore, preliminary results suggest that cyclical forces more than 1.5 times body weight are imposed on the leg long bones which may help to reduce the risk of fragility fractures. We have demonstrated the feasibility of FES rowing on land and water using adapted rowing technology that includes; a fixed stretcher indoor ergometer (adapted Concept 2, Model E), a floating stretcher indoor ergometer (adapted Concept 2 Dynamic), a turbine powered water rowing tank, a custom hydraulic sculling simulator and a single scull (adapted Alden 16). This has involved volunteers with paraplegia and tetraplegia with SCI ranging from C4 to T12 AIS A using at least 4-channels of surface electrical stimulation. FES rowers, with SCI, have competed alongside non-SCI rowers over the Olympic distance of 2000 m at the British Indoor Rowing Championships in 2004, 2005, and 2006 and the World Indoor Rowing Championships in 2006 (CRASH-Bs) in Boston, MA, USA. The best 2000 m FES rowing performance to date has been achieved by a 23-year-old male, Tom Aggar T12 AIS A, in 10 min 28 s. Moreover, two of our FES rowers with complete paraplegia have gone on to successfully compete in the Adaptive Rowing arms-only category (AM1x) at the World Rowing Championships and Paralympic Games.

FES Indoor Rowing and On-water Sculling

Although individuals with spinal cord injury (SCI) regard exercise as important and clearly can benefit from proper exercise, there are several hurdles to overcome. Most importantly, it has been suggested that an exercise intensity of at least 6 METs (i.e. oxygen consumption of 21 ml/kg/min) is required to lower the relative risk for coronary heart disease (Tanasescu et al., 2002) and to significantly improve blood lipids volumes of at least 1,200–2,200 kcal/week (Durstine et al., 2001). However, many persons with SCI can have difficulty achieving these levels (Manns and Chad, 1999). Even though some can achieve moderately high peak oxygen consumptions using their upper body muscles alone, maintaining sufficient aerobic power with small muscle mass exercise is difficult. Exercise performance may be limited by local fatigue of the highly stressed arm musculature despite adequate systemic responses.

Towards the Development of Full Motion FES Rowing with Accurate Ergometry: RowStim IV

A novel FES rowing system is presented that facilitates a near normal rowing style. The system is presently based on the Concept2 ergometer. He we present an error analysis the C2 performance monitor which suggests that a more accurate monitor will be required for medal placement in competitive rowing events.

A Design Method for FES Bone Health Therapy in SCI

FES assisted activities such as standing, walking, cycling and rowing induce forces within the leg bones and have been proposed to reduce osteoporosis in spinal cord injury (SCI). However, details of the applied mechanical stimulus for osteogenesis is often not reported. Typically, comparisons of bone density results are made after costly and time consuming clinical trials. These studies have produced inconsistent results and are subject to sample size variations. Here we propose a design process that may be used to predict the clinical outcome based on biomechanical simulation and mechano-biology. This method may allow candidate therapies to be optimized and quantitatively compared. To illustrate the approach we have used data obtained from a rower with complete paraplegia using the RowStim (III) system.

Reply to “Letter to the Editor: Consistency Among Musculoskeletal Models: Caveat Utilitor”

DAVID W. WAGNER, VAHAGN STEPANYAN, JAMES M. SHIPPEN, MATTHEW S. DEMERS, ROBIN S. GIBBONS, BRIAN J. ANDREWS, GRAHAM H. CREASEY, and GARY S. BEAUPRE Center for Tissue Regeneration, Repair, and Restoration, VA Palo Alto Health Care System, 3801 Miranda Ave, Palo Alto, CA 94304, USA; Department of Mechanical Engineering, Stanford University, Stanford, CA, USA; Industrial Design, Coventry University, Worcestershire, UK; School of Sport and Education, Brunel University, Middlesex, UK; Nuffield Department of Surgical Sciences, Oxford University, Oxford, UK; and Spinal Cord Injury Service, VA Palo Alto Health Care System, Palo Alto, CA, USA.