(Photo: frank uijlenbroek)

A quick look at the bench while a hockey match is in progress, or a visit to an elite squad coaching session, and a spectator can be forgiven for thinking that the coaches are indulging in a spot of internet shopping or trying to beat their latest 'Angry Birds' score. Lap-tops and tablets abound and at least two of the coaching staff may spend more time looking at screens than watching the players.

Why? Well, it is all to do with gaining as much information about what is happening to the players as they perform. Knowing when a player is tired or struggling with an injury is crucial in making match-changing decisions. In the old days, coaches trusted their gut feeling to be the ‘foundation stone’ of their every coaching decision. While this could sometimes have amazing results, with the coach being elevated to hero status, more often than not, the gut instinct proved a dodgy decision-making tool.

Dr Kirsten Spencer, a senior lecturer in sports coaching and performance analysis at the Coach Development Centre & Sports Performance Research Institute in Auckland, New Zealand explains: "Problems faced by coaches who relied on their memory or 'gut instinct' included memory overload, subjective bias, halo effect (performances rated higher or lower if the performer starts well…or badly), leniency error (where coaches over/under rate a performance) and highlighting (coaches only remember the best/bad performances and not the ‘bread and butter’)."

Which is why Dr Spencer's own area of specialism, performance analysis, is increasingly being used by coaches across a range of team sports. The objective measurement of players' performances gives a coach another viewpoint or angle on a  performance. As Dr Spencer points out, this does not replace the instinctive judgement of the coach but, by combining the 'scores' of measured, objectives and the coach's own opinions, key elements of that team/individual performance are quantifiable. Correct and constant application of performance analysis measurements will also give consistency to the results. 

Key elements that can be measured as part of the performance analysis process include player movement (high, low intensity, direction), team tactical analysis, technical knowledge (set pieces) and predicting performance (patterns of play).

During training and matches, players wear GPS systems (eg Catapult) and heart-rate monitors (eg Team Polar Sports). The GPS system can take a sample every five seconds and provides the coach with factors such as the distances covered by a player, the player’s velocity achieved, and the frequency, speed and duration of accelerations and decelerations. A gyro indicates the frequency of direction changes: an important point in a player's strength and conditioning training, as information about changes of direction information can indicate whether a player favours one leg/direction of turn and this knowledge may help to prevent overuse injury.

Use of a heart-rate monitor indicates the player's effort level. This is usually measured in duration and frequency within three bands: low, (0-6 kmh), medium (6.1-15 kmh) or high intensity (15.1 – 29.5 kmh ). The measurements are then expressed as a ratio – low: medium:high – so, for example, a midfield player might be working at a ratio of 25:55:20, with a lot of work in the mid intensity range, whereas a defender might be 45:30:25, with less sustained medium running, but needing to put in sudden bursts of high intensity when chasing an attacker.

Low intensity exercises are classified as standing and walking, medium intensity are jogging and running, and high intensity are fast running and sprinting). These movements are coded using a notational software system (e.g dartfish, sportscode) which records the video clip of each ‘action’.

This means that a coach is able to access accurate knowledge about the physical state of his or her players, rather than relying on when the 'players looks tired.' This is important research shows increasing fatigue impairs appropriate decision-making, which then has an impact on team performance. There is still a time and a place for those 'gut instinct' decisions, but now they can be backed up with hard facts.