There are so many ways to design a programme. The final design, however, depends on the wants and needs of the client, the equipment available and the time available (both per session and until specific goals need to be achieved).
Last Saturday (23rd June 2018) one of my clients completed the 150 miles from Seascale to Whitby. This is the second time he's completed this event; this time, however, he beat his first attempt by a significant margin. So how has the link between strength and conditioning and personal training for this client worked? Going back two or three years we used a fairly standard interval training system based predominantly on heart rate. The sessions were of varying length and intensity with target heart rates established for each session. There are lots of advantages to using heart rates, especially for longer duration intervals. However, they are much less useful for short, high intensity work (since it takes time for the heart rate to increase via the sympathetic nervous system response). Completion, though, of the 150 miles was the goal and that was achieved
In strength and conditioning, though, heart rate is often subservient to other measures of intensity. Whilst heart rate is variable over intervals (i.e it will probably get higher for any given speed as a session develops), intervals based on calorie output, Wattage or METS (metabolic equivalents) are absolute targets. Whilst speed of intervals based on heart rate will likely decline over a workout, speed of intervals in a session based on an absolute target will not. They are unrelenting; this can be a significant advantage since every period of work aims to meet a specific target zone of the absolute. These zones are always based on some form of diagnostic test, so the zones are 100% individual. The best tests I've used always give a pure and simple figure accurate to 1 unit or smaller. i.e this is the Wattage you can do over this time or this is the time or metres you did. The least useful tests have large margins of measurement (like mph or levels) - this has knock on effects in terms of how useful the diagnostic is for interval prescription.
The best tests are also really simple to conduct and absolute in terms of judgement as to when a client or athlete ends the test and what score they get. Good tests will discriminate to fine margins; less good tests leave scope for ambiguity or they allow such large margins of measurement that some get scores they scarcely deserve whilst others are underscored.
Ultimately, the 150 miles was covered so much faster for a multitude of reasons - the client was more experienced, they knew more about nutrition (the POP system) and they trained to very specific zones using Watts. Interestingly, though, we cross-referenced their endurance Wattage zone with heart rate so, when on the road, they'd know what HR to ride at.