The first aim of this study was to investigate the effect of bi-lateral ankle taping on the limits of NMF on a stationary cycle ergometer on the left, at the apex and on the right side of the P-C relationship during different phases of the pedal cycle (i.e. downstroke and upstroke). Ankle taping led to reductions in crank power on the left side of the curve, as reflected by reductions in power produced at 40-60 rpm and decrease in T0 calculated during both the downstroke and upstroke phases. Ankle taping led to increases in Copt for both phases while no difference in Pmax or power produced at 100-120 rpm were seen. Ankle taping also led to some minor changes on the extreme section of the right side of the curve which consisted of an increase of C0 calculated for the downstroke phase, but there was no difference for downstroke or upstroke power produced at 140-160 rpm.
The second aim of this study was to assess how ankle taping affected crank torque application, lower limb kinematics, inter-muscular coordination and movement variability at 40- 60 rpm, 100-120 rpm and 160-180 rpm. At 40-60 rpm, taping caused a small reduction in peak crank torque that was accompanied by a change in ankle joint kinematics and a compensatory increase in range of motion and extension velocity at the hip joint. In concomitance there was a reduction in the peak EMG, average co-activation of the ankle muscles, as well as GMAX-GAS and GMAX-SOL muscle pairs. More inter-participant variability was observed for ankle kinematics and inter-muscular coordination. At 100-120 rpm, changes in ankle joint kinematics and EMG were seen, that were compensated by changes in average co-activation (i.e. increases in GAS-TA and GMAX-RF and decreases in GMAX-GAS and GMAX-SOL). In addition, an increase in hip range of motion and reduction in peak GMAX EMG, lead to a large reduction in GMAX-GAS and GMAX-SOL co-activation. At 160-180 rpm, taping caused a reduction in peak torque during the downstroke and minimum torque in the upstroke. The more dorsi-flexed position adopted by the ankle across the pedal cycle with changes at the hip and knee joints were seen in response. Linked to the change at the ankle greater average GAS-TA co-activation of was seen in the upstroke for which there was more negative torque. Also, the changes in inter-cycle and inter-participant variability at this cadence interval were not cohesive. Additionally, the reduction in range of motion imposed by the ankle tape was not as substantial at 100-120 rpm and 160-180 rpm, compared to 40-60 rpm as indicated by lower standardised effects in Table 5.3, therefore both condition and cadence had an effect.
5.4.1 Effect of ankle taping on the left side of the P-C relationship
Our results show that ankle taping produced its largest effect on the left side of the P-C relationships and more specifically during the downstroke phase of the pedal cycle, as revealed
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by a 0.35 ± 0.49 W.kg-1 reduction in crank power at 40-60 rpm and a 0.1 ± 0.1 N·m.kg-1 reduction in T0 (Figure 5.4). While possible small reductions were also observed for upstroke power at 40- 60 rpm and T0 with ankle taping (Figure 5.4) the ratio of downstroke to upstroke power was high, similar to that observed by (Dorel et al., 2010), highlighting the greater importance of the downstroke phase for power production.
The reductions in power produced during the downstroke were accompanied by reductions in peak crank torque, produced during the first part of the pedal cycle (Figure 5.5). Ankle taping also had the greatest effect on the ankle joint kinematics at these low cadences, with the ankle less dorsi-flexed during the downstroke phase while its angular velocity was also reduced. As such, it appears that the restriction imposed by tape caused participants to plantar- flex their feet to a great degree, earlier in the pedal cycle (Table 5.2), which enabled plantar- flexion to be maintained ~5% longer in the pedal cycle, perhaps in an attempt to increase the duty cycle of the leg (Elmer et al., 2011). In compensation to the adjustment at the ankle, the range of angles covered by the hip joint was increased, associated with an increase in hip extension velocity, leading the hip extensors to operate on a different part of the power vs velocity curve. The reductions in crank torque and power during the downstroke were associated with a reduction in neural drive to the ankle musculature (GAS, SOL and TA) as illustrated in Figure 5.8. This finding suggests that these muscles were less active. The increase in peak VAS EMG suggests that this muscle was more activated, which may have resulted in an increased power production of the knee extensors during the downstroke phase. The reduction in the neural drive to plantar- flexing GAS and SOL and dorsi-flexing TA resulted in less co-activation of these agonist- antagonist muscle pairs over the downstroke (Figure 5.9). As such, ankle taping may have passively increased the stiffness of the joint, reducing the need for co-activation between agonist and antagonist muscles to actively stiffen the joint. Upon consideration of EMD, the reductions in peak EMG of the ankle muscles occurred around the same section of the pedal cycle (15-30%) for which the decrease in peak crank torque was observed. The co-activation of muscle pairs considered to work co-actively to produce and transfer force (i.e. VAS-GAS and VAS-SOL) (Zajac, 2002), were relatively unaffected by taping, perhaps due to the increase in VAS activation accounting for the decreased activation of SOL and GAS. In contrast, the average co-activation of other muscle pairs that work to produce and transfer positive force from the hip extensors to the ankle plantar-flexors during the downstroke (i.e. GMAX-SOL and GMAX-GAS) were reduced with taping, which potentially contributed to the reduction in power output observed.
In the upstroke phase, the ankle adopted a more dorsi-flexed position which may not have required the ankle joint to rotate at the same velocity for this joint action. With this new ankle position, the hip and the knee did not appear to require the same flexion velocity to return the joints back to their position at TDC. The more dorsi-flexed ankle position was concomitant with
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more TA activation in the upstroke, although this did not result in more co-activation with the plantar-flexor muscles. Substantial increases in ankle joint variability that accompanied the changes in the amplitude of the profiles, indicates that participants were not able to find a consistent solution to overcome the perturbation, nor did they execute a similar strategy as a group.
Inter-cycle variability was greater for ankle joint movement and several of the distal and proximal muscles (Table 5.7) and inter-participant variability greater for the ankle joint, most muscles and all co-active muscle pairs. Participants may have used the abundance of movement solutions offered by the human body and searched for their own unique solution to the acute perturbation at the ankle. Participants were required to produce maximal power on the cycle ergometer with little prior experience of the pedalling movement itself, let alone with the unfamiliar addition of ankle tape. Indeed, greater movement variability is typically observed in those unskilled or novice to a task (Sides & Wilson, 2012). Further to this, the varied responses in crank torque patterns and ankle joint motion between individuals may in part be attributable to Achilles tendon stiffness. It is known that tendon stiffness influences the transmission of force from the muscle, and that inter-individual variability in tendon stiffness is substantial within and between populations (e.g. men vs. women) (Magnusson et al., 2007; Waugh et al., 2013). Therefore, participants with stiffer Achilles tendons may have displayed larger reductions in power production as a result of the ankle taping, assuming that taping provided the same level of ankle stiffness across all participants.
Overall, it appears that ankle taping may have restricted the contribution of the ankle joint at a section of the P-C relationship (i.e. low cadences) for which the joint has been shown to contribute most to external power (particularly in the downstroke), while operating over a wide range of joint angles (McDaniel et al., 2014).
5.4.2 Effect of ankle taping on the middle of the P-C relationship
At the apex of the P-C relationship, Copt calculated during both the downstroke and upstroke phases were ~4 rpm higher when the ankles were taped. This finding combined with the increase in hip flexion velocity implies that the power producing muscles surrounding the hip may have been operating at a different section of their force-velocity relationship. Pmax (Table 5.1) and power produced between 100-120 rpm (Figure 5.4) during both the downstroke and upstroke phases were similar between conditions. Like observed at low cadences, ankle joint kinematics, including, range of motion and angular velocities in both its movement phases were still moderately reduced with ankle tape. As shown in Figure 5.6, a more dorsi-flexed position across the whole pedal cycle was exhibited. The range of motion of the hip and the portion of the pedal
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cycle for which it was extended increased, perhaps to account for the reduction in plantar flexion over the downstroke. Although the activation of GAS and SOL were reduced (Figure 5.8), the level of co-activation between their agonist-antagonist pairs were not affected during the downstroke (Figure 5.9) indicating that these muscles may have worked together to maintain a stable joint position, providing adequate support for force transfer to the crank. The reduction in average co-activation of GMAX with GAS and SOL over the first 50% of the pedal cycle indicates that the transfer of power from the hip extensors to the ankle plantar-flexors may have been less effective. Additionally, this decrease may not have contributed to the reduction in power due to an increase in power transfer from hip extensor muscles to the knee extensors at the same section of the pedal cycle (i.e. increased co-activation of GMAX-RF) (Figure 5.9). Less variability in crank torque profiles was seen between cycles, indicating that participants repeatedly executed a pattern which was favourable for maintaining power production in the downstroke and upstroke despite the perturbation of tape. More variability observed for proximal GMAX, VAS and RF suggests that participants explored strategies that altered the elemental variables (i.e. level of neural drive across the pedal cycle), in attempt to maintain the result variables (i.e. maintaining power).
5.4.3 Effect of ankle taping on the right side of the P-C relationship
On the right side of the relationship, there was a small increase in C0 calculated in the downstroke (Table 5.1). This may have resulted from ankle taping reducing the complexity of the movement (i.e. reducing the degrees of freedom) and as such the pedalling movement became less variable. However, taping had a trivial effect on the level of power produced at 160-180 rpm during both the downstroke and upstroke phases. Although a reduction was observed in peak crank torque during the downstroke and more negative torque, as illustrated in Figure 5.5, more torque was applied to the crank during the first half of the downstroke which may have compensated for these reductions, and thus power production was maintained. Despite the lack of difference in power at these high cadences, ankle taping still had a moderate effect on the kinematics of the ankle with a more dorsi-flexed position adopted over the pedal cycle. As illustrated in Figure 5.7, the range of angles at which the ankle joint operates (irrespective of ankle taping) narrows as cadence increases. Combining this finding with a lesser contribution of the ankle to crank power (McDaniel et al., 2014) may help to explain why the effect of tape was not like that observed when cycling at low cadences. In compensation to the reduction in ankle range of motion, the hip and knee joints moved through a greater range of angles, for which were covered at a faster velocity during extension for the knee and flexion for the knee and hip. The portions of the pedal cycle for which the hip extended, a heightened level of neural drive was observed and like in the other two cadence intervals may have been a strategy to produce power in compensation for the
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perturbation at the ankle. Interestingly, GAS and TA were more activated in the downstroke, however as noted in Table 5.6, average co-activation was not different (Figure 5.9). Only one of the two co-active pairs including GMAX were moderately reduced (i.e. GMAX-SOL), as such the power from the hip extensors to the ankle plantar-flexors was better maintained at high cadences. More variability was observed in the way participants applied force to the crank from cycle to cycle, but equivocal differences were seen in the profiles of the lower limb joints and several muscles. It appears that participants explored different execution strategies (i.e. decreased variability between cycles for GMAX and SOL, but increased variability for VAS) via the many movement solutions offered by the human body (Latash, 2012) but were still able to produce the same result variable (i.e. the maintenance of power while the ankle was taped).