Validity and Reliability of the 30-15 IFT
It is critical that the coach understands the test is both valid and reliable before they include it within their testing battery. Any test that lacks significant validity and/or reliability will produce worthless results that should not be used literally. Moreover, even a test with sufficient validity and reliability will still have some degree of error/inconsistency, but understanding how much is a crucial part of the data analysis.
The 30-15 IFT has been shown to have good test-retest reliability with a typical error of measurement to be of 0.3 km/h (ICC = 0.96), suggesting a potential difference of about 1 stage (i.e. 0.5 km/h) (3, 7).
The 30-15 IFT has been shown to be a valid and reliable measure of V02 max (8), though it is worth noting that this was only compared to the V02 max achieved during the University of Montreal Track test – otherwise known as the Léger-Boucher track test (9) – and not the typical “gold-standard” laboratory gas analysis.
Another reason coaches often use the 30-15IFT is to establish the athlete’s maximal aerobic speed, with this they will then individualise their training prescription. In this instance, it is vital the coach understands that the VIFT (i.e. the athlete’s 30-15 IFT score) is not a direct reflection of their maximal aerobic speed. This is where things get a little complicated, but we will try and keep it as simple and understandable as possible.
As an athlete can continue running, and even run faster even though they have already achieved their V02 max, maximal aerobic speed is then simply the ‘slowest’ speed an athlete will achieve their V02 max (10). As a result, an athlete may reach their V02 max at 17km/h during the 30-15 IFT, but may achieve a total score of 18.5km/h on the test. This is perhaps more easily understood by viewing Figure 4. The ability to continue running, and even increase running speed, after V02 max has been reached is known as the ‘anaerobic velocity reserve’ (3). However, this is why ‘corrective equations’ are used to calculate maximal aerobic speed from V02 max tests. All in all, this suggests that the 30-15 IFT may not be a useful marker of maximal aerobic speed.