Micropore tape

The WalkinSense® (Tomorrow Options SA, Porto, Portugal) system was used to gather digital toe pressure data whilst wearing the two footwear conditions in the same randomised order. This validated system [24 (link)] allows for individual sensors to be applied anywhere on the foot. Eight piezoresistive force, 100 Hz sensors were individually secured with Micropore™ tape (3 M, Bracknell, UK) to the following landmarks on the left foot [9 (link)] (Fig. 2).Fig. 2

Walkinsense® sensor placement 1–8 on digital landmarks, as well as experimental set up for data capture. Micropore was loosely applied to secure the sensors

(i)

Medial border of the 1^st metatarsophalangeal joint

(ii)

Medial border of the first interphalangeal joint

(iii)

Interdigital (1/2, 2/3, 3/4, 4/5)

(iv)

Proximal interphalangeal joint

(v)

5^th proximal interphalangeal joint

(vi)

Lateral border of the 5^th metatarsal head

Seeds were sterilized as described (Scarpella et al., 2004 (link)), and sown on 100 μL growth medium in a single depression slide. The slide was placed in a culture plate containing 25 mL 0.8% (w/v) agar. Plates were sealed with micropore tape (3M, VWR Intl., Mississauga, ON, CAN), to prevent desiccation. Plates were stratified in the dark at 4°C for 5 days, and then incubated at 25°C under continuous fluorescent light (100 μE m⁻² s⁻¹). Seedling leaf primordia were visualized beginning at 3 DAG. “Days after germination” (Christensen et al., 2000 (link)) are defined as days after exposure of imbibed seeds to light. For confocal imaging, the depression slide carrying the seedling was removed from the culture plate. The seedling was mounted on the depression slide under a coverslip, using sterile double-distilled water as the mounting medium. After visualization of the first leaf primordium, the coverslip was removed and the depression slide returned to the sealed culture plate. Leaves were imaged at intervals of 8–12 h, for a total maximum duration of 72 h. After the imaging period, selected seedlings were transferred to Promix BX growing medium (Premiere Horticulture, Ref Hill, PA, USA) in 7 × 7 × 8 cm pots at the approximate density of 0.1 seedling per cm² and grown under fluorescent light (100 μE m⁻² s⁻¹) for a 16-h light cycle at 22°C, followed by an 8-h dark cycle, 18°C.

A constant current stimulator (Model DS7AH, Digitimer) delivered single stimuli (1 ms pulse width) to the median nerve through Ag-AgCl surface electrodes (20 mm diameter, Conmed). The anode was placed over the median nerve lying medial to the biceps tendon in the cubital fossa. Before placing the cathode, a custom-made, hand-held surface probe was used to locate the median nerve ~2–3 cm proximal to the anode, just medial to the biceps muscle. The optimal location for median nerve stimulation was defined as the position that elicited the largest and clearest H reflexes and M waves in the FCR using the lowest stimulus intensity. Once located, a surface cathode was placed over the median nerve at this site. A constant pressure was maintained over the cathode with a cotton gauze pad held in place with Micropore tape (3M Health Care, Neuss, Germany).

In the upper limb, subjects were asked to perform a repetitive precision grip task. A length of compliant plastic tubing (length 19cm, Portex translucent PVC tubing 800/010/455/800; Smith Medical, Ashford, UK) was attached to the index finger and thumb with Micropore tape (3M Health Care, Neuss, Germany), and subjects were asked to oppose both ends of the tubing when prompted by visual and auditory cues. This auxotonic task–so-called because force increases with displacement in a spring-like fashion–required a minimum force of 1N [35 (link)] and was similar to a precision grip task used in our previous studies, albeit without measuring digit displacement [36 (link),37 (link)]. In the lower limb, subjects were asked to dorsiflex ankle and toes in the air while resting the heel on the ground. Subjects produced 4s of contraction alternating with 2s of relaxation, and at least 100 repetitions. Visual feedback of raw EMG traces was provided to facilitate consistent task performance.