A POL or PYR model works better than THR for both elite and club level endurance athletes. Seiler, who popularized the POL model recently suggested the three level zones could be combined into a binary model split at LT1 with POL and PYR basically being treated as the same.
The argument between POL/PYR and HIT may actually be false. The overall amount of HIT volume should remain constant and therefore once training volume drops below 5 hours per week (4 hours LIT, 1 hour HIT or 80/20) HIT volume becomes more dominant and the model naturally moves to HIIT. On average, approximately two HIT sessions per week at around 1 hour total TIZ appears sufficient to induce performance and physiological adaptations without overreaching during the long term. Conversely as training volumes increase LIT will dominate, over 90% at volumes of 20 hours per week. High volumes of LIT improves base and long term fitness, As Stalin is reputed to have said “quantity has a quality all of its own”.
It appears that THR leaves athletes tired over the medium term and liable to burn out without bringing the hoped for gains in performance as the body does not have enough recovery time. There is some research1 showing recovery above the LT1 level is much slower but adaptations below LT2 are limited, our so called “junk miles”. All the pain for little gain.
Pyramidal TID patterns have also been found in a study on elite XC sprint skiers during a six month pre-season period. The World-Class skiers in that study had an intensity distribution in their training of 88% LIT, 7% MIT and 5% HIT (SG/TIZ method).
1.) Seiler S, Haugen O, Kuffel E. Autonomic recovery after exercise in trained athletes: intensity and duration effects. Med Sci Sports Exerc. 2007 Aug