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5.2.3.1The limits of NMF during maximal cycling exercise

Force-velocity test

A custom built isoinertial cycle ergometer equipped with 172.5 mm instrumented cranks (Axis Cranks Pty, Australia) was used to run the F-V test. Tangential force (i.e. crank torque) was recorded from the left and right cranks separately via load cells at a frequency of 100 Hz and sent in real time to Axis bike crank force vector analyser software (Swift Performance Equipment, Australia). A static calibration of the instrumented cranks while connected to Axis bike crank force vector analyser software was performed prior and after data collection, following procedures previously described (Wooles et al., 2005). The external resistances used during the F-V test (including warm up) were adjusted and controlled using an 11-speed hub gearing system (Shimano Alfine SG-S700, Osaka, Japan). The cycle ergometer saddle height was set at 109% of

B C

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inseam length (Hamley & Thomas, 1967), while the handlebars were set at a comfortable height for each subject. At the beginning of the sessions, subjects performed a standardized warm-up of 5-min of cycling at 80 to 90 rpm, at a workload of 100 W and culminated with two practice sprints. Following 5-min of passive rest, subjects performed two F-V tests in the same session, one in the CTRL condition and one in the TAPE condition. Each F-V test consisted of three 4-s sprints interspersed with a 5-min rest period. More specifically, the different sprints completed by each subject were as follows: 1) sprint from a stationary start against a high external resistance; 2) sprint from a rolling start with an initial cadence of ~70 rpm against a moderate external resistance and 3) sprint from a rolling start with an initial cadence of ~100 rpm against a light external resistance. For each sprint, subjects were instructed to produce the highest acceleration possible while remaining seated on the saddle and keeping their hands on the dropped portion of the handlebars. Subjects were vigorously encouraged throughout the duration of each sprint.

Analysis of T-C and P-C relationships

The methods for analysis of T-C and P-C relationships are the same as those described for the identification of maximal pedal cycles outlined in Study one, (section 3.2.3.1) and Study two (section 4.2.4.1). Briefly, average torque and cadence were recorded and calculated from the Axis cranks, over a full pedal cycle (i.e. LTDC-LTDC and RTDC-RTDC), downstroke (i.e. LTDC- LBDC and RTDC-RBDC) and upstroke (i.e. LBDC-LTDC and RBDC-RTDC) portions of the pedal cycle for each leg separately (Figure 5.2). Power was then calculated using Eqn. 1. The same maximal data point selection and curve fitting procedures as outlined in Study one (sections 3.2.4.1 and 3.2.4.2) were implemented for full pedal cycle, downstroke and upstroke T-C and P- C relationships. Average values of power produced in the downstroke and upstroke phases were then calculated for CTRL and TAPE for three cadence intervals: 40-60 rpm (low cadences), 100- 120 rpm (moderate cadences) and 160-180 rpm (high cadences) using between 5 and 10 pedal cycles for each participant. Pmax, Copt and C0 were calculated from regressions fit to each of the P- C relationships (i.e. downstroke and upstroke phases), while T0 was calculated from regressions fit to each of the T-C relationships.

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Figure 5.2. Sections of the pedal cycle. A full pedal cycle is defined between TDC and TDC, while the downstroke portion of the pedal cycle is defined between TDC and BDC and the upstroke portion of the pedal cycle is defined between BDC and TDC.

5.2.3.2Control of the pedalling movement

Crank torque profiles

In comparison to studies one (Chapter 3) and two (Chapter 4) for which total crank torque was recorded (i.e. sum of left and right crank force), the use of Axis cranks in this study enabled the assessment of force delivered to the left and right cranks separately, allowing patterns of force application during the downstroke and upstroke phases of the pedal cycle to be illustrated and quantified. Crank torque signals were time normalised to 100 points, like study one and two using the time synchronised events of left and right top-dead-centre to create crank torque profiles for each pedal cycle. Average crank torque profiles were calculated for three cadence intervals, 40- 60 rpm, 100-120 rpm and 160-180 rpm using between 5 and 10 pedal cycles for each participant. Average values of peak and minimum crank torque were then identified from these profiles for the three cadence intervals.

Kinematics of the lower limb joints

The marker setup adopted and three-dimensional kinematic data collected was as per the methods described for Study two in section 4.2.4.2 and illustrated in Figure 4.3. The neutral position of the ankle (i.e. when standing in anatomical position) was approximately 90°. Average hip, knee and ankle joint angle and angular velocity profiles were created from the same pedal cycles (encompassing both left and right pedal cycles) as those used for the analysis of mechanical data

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for 40-60 rpm, 100-120 rpm and 160-180 rpm intervals. Minimum and maximum joint angles for the hip, knee and ankle were obtained for each pedal cycle within these cadence intervals, and the difference between the minimum and maximum values was used to obtain joint range of motion (ROM). Joint angular velocity profiles of the extension (plantar-flexion) and flexion (dorsi- flexion) phases of movement for each of the joints were also constructed using the same pedal cycles within the three cadence intervals. Average peak extension/plantar-flexion and flexion/dorsi-flexion joint angles, ROMs and average extension (plantar-flexion) and flexion (dorsi-flexion) angular velocities were calculated from the profiles for the three cadence intervals. Using the zero crossing of the angular velocity profiles, the section of the pedal cycle (i.e. in percent of the pedal cycle) where the joints moved from flexion/dorsi-flexion to extension/plantar-flexion and from extension/plantar-flexion to flexion/dorsi-flexion were also identified for the pedal cycles corresponding to the three cadence intervals.

EMG activity of the lower limb muscles

Surface EMG signals were recorded from four muscles surrounding the left and right ankle joints: GAS, TA, SOL and from GMAX, VAS, RF and HAM muscles on the left only. Attachment of the electrodes and filtering process of the raw EMG signal were as per the methods outlined in Study one (section 3.2.3.2) and Study two (4.2.4.2). As per these studies, synchronisation of EMG and crank torque signals was achieved via the closure of a reed switch which generated a 3-volt pulse in an auxiliary analogue channel of the EMG system which synchronised Axis crank position with the raw EMG signals.

Processed EMG signals were time normalised to 100 points and the amplitude of the RMS for each muscle normalised to the maximum (peak) amplitude recorded during the testing session according to methods previously recommended (Rouffet & Hautier, 2008). Average EMG profiles were then created from the normalised EMG signals for 40-60 rpm, 100-120 rpm and 160-180 rpm using the same pedal cycles used for the analysis of mechanical and kinematic data. Average peak EMG amplitude was then calculated for the downstroke portion of the pedal cycle for GAS, SOL GMAX, VAS, RF and HAM and both the downstroke and upstroke portions of the pedal cycle for TA at each cadence interval. As muscle force (i.e. force applied to the crank) occurs later in the pedal cycle than EMG activity (i.e. EMD) (Cavanagh & Komi, 1979; Ericson et al., 1985; Van Ingen Schenau et al., 1995; Vos et al., 1991), to enable associations to be made between muscle activation and crank torque patterns it was necessary to shift the EMG signal by a given time period or in the present study a given portion of the pedal cycle. EMD has been shown to lie between 60 ms and 100 ms dependent on the muscle, but reports suggest it is approximately 90 ms in most of the leg muscles during cycling regardless of their functional roles

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(i.e. mono-articular or bi-articular) (Van Ingen Schenau et al., 1995; Vos et al., 1991). These EMD times appear to remain consistent regardless of cadence (Li & Baum, 2004) and movement complexity (Cavanagh & Komi, 1979) as such at 40-60 rpm a forward EMG shift of approximately 6% would be required (i.e. 60 ms/1200 ms), while at 100-120 rpm and 160-180 rpm the shift would be 15% and 23% respectively.

Co-activation profiles were calculated for GAS-TA, SOL-TA, GMAX-GAS, GMAX SOL, GMAX-RF, VAS-HAM, VAS-GAS and VAS-SOL muscle pairs at 40-60 rpm, 100-120 rpm and 160-180 rpm intervals for CTRL and TAPE using Eqn. 2 stated in Section 3.2.3.3. An average CAI value was then calculated for each muscle pair for the three cadence intervals for CTRL and TAPE conditions.

Variability of crank torque, kinematic, EMG and co-activation profiles

Variance ratios (VR) were used to calculate inter-cycle and inter-participant variability in crank torque, kinematic, EMG and co-activation profiles for CTRL and TAPE. Pedal cycles between 40-60 rpm, 100-120 rpm and 160-180 rpm were used in Eqn. 3 to produce a VR for each participant (inter-cycle variability) and also a VR between subjects (inter-participant variability) like described in study two, section 4.2.4.2.

Figure 5.3. Experimental set up for data collection including the equipment used for the acquisition of mechanical, kinematic and EMG data.

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