Methods
Two studies are included in this report. Study 1 aimed to test the acceptability of magnetic femoral stimulation and reproducibility of TwQ in a small group of older people with sarcopenia; Study 2 aimed to relate magnetic femoral stimulation results to a range of measures of physical function using baseline data from a clinical trial in older people with a history of falls. Both studies followed the principles of the declaration of Helsinki. Study 1 was approved by East of Scotland Research Ethics Committee (approval number 13/ES/0045); Study 2 was approved by Scotland A Research Ethics committee (approval number 13/SS/0086), and was registered as a clinical trial (ISRCTN58995463) with approval from the UK Medicines and Healthcare Regulatory Authority (EudraCT number 2013-001677-24; CTA number 21726/0281/001).
Study 1
Community dwelling people > 65 years with sarcopenia and self-reported difficulty with one or more activities of daily living (ascertained by an open question to participants) were recruited through the Scottish Primary Care Research Network. We excluded people who had metal implants or metal fragments in the lower limbs, previous internal fixation of lower limb fracture, vascular stents, those with internal cardiac defibrillators, cardiac pacemaker and implanted nerve stimulators; any condition (e.g. severe osteoarthritis) that was likely to be aggravated by lower muscle contraction; cognitive impairment precluding informed consent; inability to mobilise without human assistance and those residing in a nursing home.
Participants attended a baseline and follow up visit after 2 weeks. At the baseline visit, potential participants were screened for sarcopenia, defined as: Total skeletal muscle mass (SMM) measured by bioimpedance [9] of < 10.76 kg/m2 for men or < 6.76 kg/m2 for women and either low handgrip strength (< 30 kg for men or < 20 kg for women) or low gait speed (< 0.8 m/s for the 4 m walk). Body composition was measured using bioimpedance (BIA) (Akern Bodygram Pro 101 v.3.0; Akern Srl, Florence, Italy). The Janssen formula [10] was used to calculate total skeletal muscle mass/height squared (SMM/H2). Handgrip strength was measured in the non-dominant hand using a Jamar dynamometer (Lafayette Instruments, Lafayette, Indiana, USA). The best of three attempts was recorded.
Outcomes
Outcomes were measured at baseline and at 2 weeks. Acceptability of magnetic stimulation was assessed using a visual analog scale, which asked participants to indicate (a) the degree of discomfort whilst undertaking the Magstim test and (b) how tired they felt at the end of the study. Scales were anchored by statements, e.g. 0% was anchored by ‘no discomfort’ and 100% by ‘extreme discomfort’. The final question asked if they would have the magnetic stimulation test again. The time in seconds taken to walk 4 m at their usual pace was assessed, with the faster of two attempts recorded. The Short Physical Performance Battery (SPPB) [11] was performed according to standard protocol. Isometric quadriceps maximum voluntary contraction strength (QMVC) was measured in a semi reclining position with the knee joint at 90 degrees using a Biopac tension dynamometer (Biopac Systems inc. California, USA). The measurement was taken on the right leg unless the participant had a metallic hip joint on this side. An inelastic strap was placed around the ankle and connected to the dynamometer mounted to the couch. The participant was then instructed to kick their foot out, pushing hard against the strap, hold for 10 s and then relax. This procedure was repeated twice. QMVC was taken as the highest mean force that could be sustained over one second. Participants undertook a 6 minute walk test along a 25 m course at their normal walking pace, using a walking aid if needed. Standardised encouragement was given. The distance covered was recorded as a measure of submaximal endurance.
Magnetic femoral nerve stimulation
The greatest twitch tension generated in the quadriceps (TwQ) was measured using the Magstim 200 system (Magstim Company Ltd., Whitland, UK). A double 70 mm coil in the shape of a figure of eight was used. Participants were placed in a semi reclining position with a strap around the ankle as described before. The crossover point of the coil was then positioned over the groin to stimulate the femoral nerve using a single biphasic stimulus; the femoral artery was palpated to guide placement over the femoral nerve. A range of magnetic outputs (60, 70, 80, 90 and 3 times at 100%) were applied to check supramaximality of TwQ response. A 30 s interval was allowed between each reading.
Study 2
For study 2, we used baseline data from a double-blind randomised controlled trial of the effect of perindopril, an angiotensin converting enzyme inhibitor (ACEi) on postural stability in older people. Details of the inclusion and exclusion criteria and study population have been reported previously [12]. QMVC was measured as described for Study 1, but fatigability was also assessed by performing repeated QMVC measurements with no break between 3 s efforts. The number of efforts performed before QMVC fell to 70% of maximum was recorded as a measure of endurance. In addition, after initial TwQ testing, three measurements at 100% were performed immediately and after a 10 min rest to estimate the effect of fatigue and recovery on TwQ following repeated QMVCs. Fatigability was further tested by measuring TwQ following the 6 minute walking test described above.
Statistical analysis
We used Pearson’s correlation coefficients to compare baseline TwQ with other baseline measures of physical function, and used two-way, random effects intraclass correlation coefficients to test reliability, comparing baseline and follow up TwQ. All analyses were performed using SPSS v21 (IBM, New York, USA) and a 2-sided p value of < 0.05 was taken as significant for all analyses.