DETERMINACIÓN DEL IMPACTO POTENCIAL

This thesis provides new insight into the limits of neuromuscular function on a stationary cycle ergometer. However, interpretation of the data must be considered in the context of the limitations of the research.

General limitations

 Due to the crank torque system employed in the first and second study measuring total crank torque, the contribution of the two limbs could not be dissociated. However, as the thesis progressed, measuring forces on the left and right cranks separately became possible (i.e. Axis cranks) was available and as such was implemented in study three.

 The number of pedal cycles used to calculate average values and variance ratios for a given cadence interval varied depending on the cadence interval assessed. Due to a revolution taking more time to complete at low cadences compared to high cadences, and because the sprints were performed on an isoinertial cycle ergometer, fewer pedal cycles was available for inclusion in the analysis of low cadence intervals. For example, in study

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three, approximately five pedal cycles were used for analysis of the 40-60 rpm cadence interval, while approximately 10 pedal cycles were used for the analysis of the 160-180 rpm cadence interval. In addition to the effect of cadence, the number of pedal cycles included within an interval was also participant dependent (i.e. some participants could overcome the external resistance more rapidly than others leading to fewer pedal cycles performed at the beginning of a sprint).

 Although, the co-activation profiles of different muscle pairs were illustrated, values used to compare conditions were represented by an average value calculated over the full pedal cycle. As such co-activation was not calculated over different portions of the pedal cycle, except for average co-activation calculated for agonist-antagonist ankle muscles in the downstroke and upstroke phases in study three.

 Specific cadence intervals (i.e. low, moderate and high cadences) were used in the three studies to assess the effect of data selection procedures, training interventions and ankle taping on the production of power, as such, the effect of these outside of the investigated cadence intervals is unknown and only informed assumptions can be made regarding potentially changes.

Study one limitations

 With regards to the data selection procedures implemented in study one, when only one experimental data point was available for a given 5 rpm cadence interval, it was selected as a maximal cycle/data point unless the power/torque values were substantially lower than those of maximal cycles selected from the adjacent intervals. Consequently, a data point for that given cadence interval was not included in non-maximal cycle T-C and P- C relationships which lead to a small discrepancy in the number of maximal and non- maximal cycles (i.e. 24 ± 3 pedal cycles vs. 19 ± 5 pedal cycles).

Study two limitations

 Although EMG could be used to assess patterns of muscle activation and co-activation of muscle pairs, EMG amplitude could not be compared before and after training in study two due to issues with normalisation of the signal. The location of the EMG electrodes on the lower limb muscles were marked at baseline and were continued to be marked over the training period until the post-training session to ensure consistency of electrode placement. However, issues arose regarding the most appropriate reference value to normalise EMG signals to. The maximal intensity of the sprint bouts performed in training has the potential to modify maximal levels of activation for those muscles

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trained, which meant that normalising signals to peak EMG values like recommended in previous research (Rouffet & Hautier, 2008) was not an appropriate method for this study.

 The use of dual-energy x-ray absorptiometry may have provided a more robust quantification of total and lean muscle volume in study two, although this equipment was not available at the time the research was conducted. However, to ensure consistency within and between subjects the same experimenter performed all anthropometric measurements pre- and post-training.

 Due to participants displaying highly variable responses to high velocity training, a larger sample size (i.e. n >8) may have been required to enable the full effect of this training intervention to emerge. Further, matching groups for number of contraction cycles completed as per the work of (Tomas et al., 2010), rather than time spent training (i.e. time for which muscles were recruited), may have underestimated the training volume required to improve power production at fast movement velocities.

Study three limitations

 Ankle taping did not affect the kinematics of the ankle joint in the exact same way for all individuals (i.e. ankle joint ROM). Although, the same researcher performed the same taping procedures on all participants to ensure consistency and reduce the level of experimenter variability, variations in ankle range of motion were seen between participants at each of the different cadence intervals assessed (i.e. 40-60 rpm, 100-120 rpm and 160-180 rpm). Although the tape used was rigid, it still offered some laxity and participants may have produced forces during the sprints that the tape could not withstand causing it to deform, changing ankle joint range of motion within a pedal cycle. In the piloting phase of this study, alternative methods for stiffening the ankle joint were considered such as ankle-foot orthoses. However, these devices were not deemed sturdy enough and therefore unsafe to use during maximal cycling exercise.

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