Interface Design: Velocity Parameterisation

The initial seminar component of the second workshop successfully upskilled the group of coaches with knowledge about how to interpret rowing acceleration and velocity graphs and the concept of velocity parameterisation. Some participants had greater initial familiarity with the topic and there was also a range of spe- cialisms within the group. Such a topic would appeal to the mathematical and scientifically minded coaches although attempts were made to present the inform- ation in a range of formats to appeal to the whole group. At this stage, the group were engaged with the research with an appreciation of how it might positively impact upon rowing performance. Two coaches present would be involved in the future training study and showed particular interest.

The interface design task was approached in the same way as for the stroke arcs. Following an introduction to the components of a good user interface, four groups set about designing relevant concurrent interfaces. Only two interfaces resulted from the design task which was disappointing. This may have been due to the complexity of the rowing skill causing confusion as to how it might be portrayed or because the mean age of the coaches was greater than the athletes in the pilot workshop resulting in some resistance to being creative and open with ideas.

Figure 4.11 was produced by a coach with a research interest in computer based user interfaces. He was inspired by one of the graphs presented during the seminar and a hospital heart rate trace. A flat trace represented zero acceleration, green a positive acceleration and red a negative acceleration. Regardless of the polarity of the acceleration, an envelope above and below the centre line would be presented. History was discussed with the interface giving an athlete sufficient time to absorb the previous stroke if rowing at training intensity. The interface had been specifically designed with acceleration emanating from the centre of the screen and scrolling from left to right as it was felt that this would focus the athlete’s attention and be the most natural way to absorb the information.

Video synchronisation was discussed alongside the interface with a cross hair used to indicate location. This would be most relevant for data review rather than real-time feedback. Target traces were also mentioned with the model being either a pre-programmed stroke or the best effort previously achieved.

Conversation led to the addition of stroke metrics on this interface with a second participant citing his design (figure 4.12). On this interface, a range of parameters would be provided including stroke rate, pace (split), time elapsed as well as measures of foot stretcher, handle and resultant force and the amount of time spent in particular stroke zones. The central bullseye component was likened

Figure 4.11: Scrolling acceleration interface design originating from coach work- shop.

to a ‘G-Force’ sensor with a central position being good and a marker away from the centre being bad. It was appreciated that the bullseye would move very quickly. While further clarification of this interface was sought after the workshop, exact clarity on the operation of the bullseye was not clear. A follow-up workshop may have produced further concurrent designs but could not be organised and therefore a further concurrent design was conceived by the investigator.

Two versions of the scrolling interface were implemented. The original (figure 4.13) replicated the design produced at the workshop. In the first instance no model was included nor any video synchronisation. It was also kept as a purely concurrent interface and therefore no stroke metrics were included. Following user feedback (chapter 6), a second version of this interface was produced with data updating from the right hand side of the screen and accelerations only appearing one side of the line depending upon polarity (figure 4.14). This made the inter- face look similar to graphs presented in reports and therefore more intuitive to interpret. It also meant that polarity was indicated by both screen location and colour.

The bullseye interface was simplified to remove the stroke level numerical con- tent. Further conversations with the designer, who was also one of the future study coaches, led to a design that had a fixed radius black circle to represent zero acceleration, an expanding green circle to represent positive acceleration (fig-

Figure 4.12: Bullseye interface design originating from coach workshop.

Figure 4.14: Modified right to left scrolling acceleration interface.

(a) Positive acceleration. (b) Negative acceleration.

ure 4.15a) and a contracting red circle representing negative acceleration (figure 4.15b). Pilot testing of this interface showed that the resolutions of small acceler- ations were masked by large accelerations around the front reversal of the stroke and hence a logarithmic acceleration scale was used.

Figure 4.16 shows the concurrent interface that was designed by the investig- ator. An attempt was made to distinguish the loading of the foot stretcher from the resultant forces applied during the drive of the stroke. The left hand ‘Recovery’ panel displayed only foot stretcher force in the same plane as handle travel during mid-recovery to mid-drive. In reality, the horizontal axis of this panel was time since it was discovered that graphing foot stretcher force against handle position led to a discontinuous and unrepresentative trace. Horizontal scaling was calcu- lated by the time to complete this section of the previous stroke. The ‘Drive’ panel displayed acceleration against handle position from the minimum to the maximum handle excursion. Scaling for this panel was set through the user interface control panel based on athlete typical stroke parameters.

Figure 4.16: Split screen interface.

Historical data was integrated into the design. Concurrent information was traced using a red spot with the current stroke displayed as a red line. At the start of the next stroke for that panel the red line would become a blue line, the oldest of the five historical blue lines would be removed and the new stroke information would begin to appear in red.

The terminal interface would display either the quality of catch, drive or stroke measure for the previous stroke as a numerical value. No specific coach input was given to this design due to its simplicity although two screens were developed. The first showed the value in red enclosed within a box and a target value in black.

Figure 4.17: Statistics history interface.

Figure 4.17 shows the second terminal interface that plotted the metrics from 10 historical strokes with latest stroke added to the left of the graph. In both cases, targets and graph scales were set through the user interface control panel.

The concurrent and terminal interfaces were piloted with one of the coaches involved with the training study. A full description of the results of the user testing and evaluation study are available in chapter 6.