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PURPOSE: The aim was to compare mesocycles with progressively increasing workloads and varied training intensity distribution (TID), that is, high-intensity (HIGH, > 4 mmol·L blood lactate), low-intensity (LOW, < 2 mmol·L blood lactate) or a combination of HIGH and LOW (referred to as "polarized" POL) on 5000-m running time and key components of endurance performance in recreational runners. METHODS: Forty-two runners (peak oxygen uptake (V˙O2peak): 45.2 ± 5.8 mL·min·kg) were systematically parallelized to one of three groups performing a 4-wk mesocycle with equal TID (two to four training sessions) followed by a 3-wk mesocycle with increased weekly training impulse (i.e., 50% increase compared to the first 4-wk mesocycle) of either HIGH, LOW, or POL and 1 wk tapering. V˙O2peak, velocity at lactate threshold and running economy were assessed at baseline (T0), after 4 wk (T1), 7 wk (T2), and 8 wk (T3). RESULTS: The 5000-m time decreased in all groups from T0 to T2 and T3. V˙O2peak increased from T0 to T2 and T3 (P < 0.03) with HIGH and from T0 to T2 (P = 0.02) in LOW and from T0 to T3 (P = 0.006) with POL. Running economy improved only from T1 to T3 and from T2 to T3 (P < 0.04) with LOW. An individual mean response analysis indicated a high number of responders (n = 13 of 16) in LOW, with less in HIGH (n = 6/13) and POL (n = 8/16). CONCLUSIONS: On a group level, HIGH, LOW, and POL improve 5000-m time and V˙O2peak. Changes in running economy occurred only with LOW. Based on the individual response of recreational runners the relative risk of nonresponding is greater with HIGH and POL compared with LOW.
Zinner et al. (Tue,) studied this question.