REF-942 · Pedlar et al., 2018 · Journal of Applied Physiology, Vol. · Paper · PubMed

Cardiovascular response to prescribed detraining among recreational athletes

Blimited evidenceMeasured on recreational to trained athletesWritten before October 2026, being re-checked

Recreational runners (n = 21; 48% male; age 34 ± 7 yr) trained for 18 wk (~7 h/wk) up to the 2016 Boston Marathon and then limited all exercise to <2 h/wk, with no session over 1 h, for 8 wk. Heart structure and function, exercise capacity and plasma volume (PV) were measured at peak fitness (10-14 days pre-race) and again 4 wk and 8 wk post-race.

Treadmill performance fell step by step, confirming detraining. By 4 wk, PV, left ventricular wall thickness, LV mass and right atrial area had all dropped; by 8 wk, the right ventricle chamber had shrunk, with no further fall in PV or LV wall thickness. Reverse cardiac remodelling ran on a time course specific to each structure and was largely independent of PV contraction.

Participants

21 recreational runners, age 34 ± 7 yr, 48% male, who trained for and ran the 2016 Boston Marathon.

Protocol

18-wk training program (~7 h/wk) ending in the marathon.
Prescribed detraining for 8 wk: total exercise <2 h/wk, no single session >1 h.
Assessments at peak fitness (10-14 days before the marathon), 4 wk and 8 wk postmarathon: cardiac structure and function, exercise capacity, PV.
Mixed linear modeling adjusted for age, sex, V̇o2peak and marathon finish time.

Key Results

After 4 wk of detraining: PV Δ -6.0% (P < 0.01), LV wall thickness Δ -8.1% (<0.05), LV mass Δ -10.3% (P < 0.001), right atrial area Δ -8.2% (P < 0.001).
After 8 wk: right ventricle chamber size reduced (end-diastolic area Δ = -8.0%, P < 0.05), without further reductions in PV or LV wall thickness.
Physiological detraining was evidenced by serial reductions in treadmill performance (no figure in the abstract).
LV chamber volumes appeared less responsive to detraining.

Practical Application

"What do I lose if I mostly stop for a month or two after my marathon?" In 21 recreational runners held to <2 h/wk for 8 wk, plasma volume fell 6.0% and left ventricular mass 10.3% within the first 4 wk, the right ventricle followed by 8 wk, and treadmill performance declined at each test. The early loss is fast and central; most of it is in by week 4.
The off-season cost comes from the size of the cut, not from stopping entirely: these runners still exercised a little. Not from this paper; the base's own practice: keep a short off-season and do not let intensity drop to zero (SYNTH-76); what holds fitness on a reduced load is in REF-374 and REF-587.
Inference, not tested here: because plasma volume contracts within weeks, heart rate at a given easy pace is expected to sit higher on return; treat that as detraining, not illness.
Retraining was not measured, so this paper cannot say how fast the losses come back.

Limitations

No control group; changes after a marathon include recovery from the race itself.
n = 21; the size of the performance decline is not given in the abstract.
Exercise was restricted, not stopped; adherence to the limit is not described in the abstract.
No retraining phase.
Written from the abstract and record metadata only (full text not read).
How this entry was checked and changed
Why this level

uncontrolled pre-post, n = 21