Muscle force was recorded on a computer at 1000 Hz using Chart 4 V4.1.2 (AD Instruments, Oxford, UK). Two custom made saline soaked electrodes (9 × 18 cm) were placed just above the patella and over the muscle belly of the knee extensors in the proximal third part of the thigh of the non-dominant leg. The position of the electrodes was marked using permanent pen to ensure accurate placement on subsequent tests. For all electrically evoked test procedures, stimulation was provided through an electrical muscle stimulator (Model DS7A, Digitimer TH-302 in vivo Limited, Welwyn Garden City, UK) and pulses were controlled by a NeuroLog pulse generator (Digitimer Limited, Welwyn
Garden City, UK). Participants conducted three 5 second sub-maximal contractions
(~200 N) each testing session to SHP099 concentration become accustomed to the experimental set up. Isometric Maximal Voluntary Contraction (MVC) Participants produced a 3 to 5 second maximal voluntary contraction (MVC) with strong verbal encouragement. When the effort was not considered maximal the procedure was repeated after 2 minutes rest. Approximately 90% of MVC’s were PD0325901 maximal effort on the first attempt. The maximal force was taken as the absolute highest value during the contraction. Interpolated Doublet (% Voluntary Activation) During Isometric Contraction A doublet pulse (two maximal single twitches separated by 10 ms) was applied to the knee extensors during the plateau phase of the MVC contraction, and immediately after the MVC when participants returned to rest (potentiated doublet). Percent voluntary activation (%VA) was calculated (Equation 1). The following parameters were calculated for the potentiated doublet: (a) peak force (N), the maximal force value of the doublet; (b) contraction time (s), the time between the first derivation from baseline and peak force; (c) average rate of force development (N·s-1), peak force/contraction time; (d) half relaxation time (s), the time taken to fall from peak
force to half of the value during the relaxation phase; (e) maximal rate of force development (N·s-1), the highest value of the first derivative of the force signal; and (f) maximal rate of force decrease (N·s-1), the lowest value Phosphatidylinositol diacylglycerol-lyase of the first derivative of the force signal. (1) Isometric 20 Hz and 50 Hz stimulation 20 Hz and 50 Hz stimulations (0.5 s duration), with 30 second rest between stimulations, were applied to the knee extensors using the sub-maximal twitch current (group mean ± SD; 420 ± 77 mA). A sub-maximal current gives a reliable estimate of contractile properties and is more tolerable for participants. A ratio of the forces at 20 Hz and 50 Hz was calculated, a reduction in the ratio indicates the presence of low frequency fatigue.