2.2.4. Muscle Function

To assess muscle function, vertical jump (VJ) height (m), maximum sprint time (s), grip strength (kg), and isometric knee extension maximal voluntary contraction (KE iMVC, N) were measured. Prior to the tests, all participants were taken through a standardised warm up which aimed to increase heart rate to over 120 bpm (Polar H10 chest heart rate monitor, Polar Electro, Kempele, Finland) and dynamic stretches with focus on the muscles around hips, knees, and ankles. Participants were given two attempts at each test, with 1 min rest in between, and the best result was recorded. VJ height (m) was measured using a jump mat (Probotics Inc., Esslinger court, Huntsville, Alabama) in two conditions—with and without arm swing. Nuzzo, Anning [32] reported the jump mat to be a reliable piece of equipment to measure VJ height in males (ICC = 0.93, coefficient of variation (CV) = 2.3%) and females (ICC = 0.90, CV = 6%) over two separate days.

Maximum sprint speed was assessed over 10 m. Two sets of sensory timing gates (Brower timing system, Wireless Sprint System 2007, Brower, Draper, UT, USA) were set up 1 m apart at either end of a 10 m distance. Participants performed two sprints with a standing start 0.60 m behind the first set of gates. This was shown to be a reliable method when measured on two separate days (ICC = 0.912, p < 0.01) [33].

Grip strength was assessed using a handgrip dynamometer (Jamar plus, Sammons Preston Rolyon, Bolingbrook, IL, USA). Participants chose their most comfortable grip position, and two maximal grip efforts were performed while standing with the elbow as extended as possible and the arm raised in front of the body level with the shoulder. Both tests were separated by 1 min, and the highest value was recorded. This current study showed a high test-retest reliability in men with CP and TDC (ICC = 0.996–0.998, both p < 0.001).

To record KE iMVC, participants were seated on a custom-made isokinetic chair fitted with a portable load cell (Manchester Metropolitan University, Manchester, UK). Their arms were across their chest, and the load cell attached around the dominant kicking leg (or the most paretic side in the CP group) with the knee at 90° flexion. The tested leg was fastened to a force transducer placed 5 cm above the lateral malleolus. Participants were instructed to extend the fastened leg maximally, and verbal encouragement was given during the measurement. Two trials were performed with 1 min break between each trial. The highest force produced was digitised using an analogue-to-digital converter, displayed by a self-displayed and coded program (MyLabView, National Instruments, Berkshire, UK) [34]. KE iMVC values were also presented relative to VL ACSA (KE iMVC/ACSA), BM (KE iMVC/BM), and LBM (KE iMVC/LBM).