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.