REF-1303 · Chen et al., 2009 (with Chen et al., 2007) · Journal of Sports Sciences · Paper · PubMed

How long after a first big downhill run before hard running?

In untrained men, running economy at 80-90% VO2max was still worse 2 and 5 days after 30 min of steep downhill; at 70% it was not. Probably a first exposure (B).

Main caveat: Read from the abstracts only; magnitudes at each intensity (2009), the per-intensity results (2007), participant characteristics and individual responses could…
limited evidenceMeasured on non-athletes and recreational people

Chen and colleagues tested whether running economy measured at a high intensity is affected more than at a low one after downhill running. Fifteen untrained young men ran on the level at 70, 80 and 90% of VO2max (5 min each) before and 2 and 5 days after a 30-min downhill run at −16% at the speed of their 70% VO2max.

Downhill running reduced maximal isometric knee-extensor strength, caused soreness and raised plasma creatine kinase and myoglobin, all lasting 5 days.

All running-economy and kinematic measures (oxygen uptake, ventilation, respiratory exchange ratio, heart rate, perceived exertion, blood lactate, stride length and frequency) were significantly changed from baseline at 2 and 5 days at 80% and 90% of VO2max, but not at 70%.

In the companion study (2007), ten young men ran 30 min at −15% at 70% VO2peak and were tested at 65, 75 and 85% VO2peak before, immediately after and 1-5 days later: knee-extensor strength fell 7-21%, creatine kinase and myoglobin rose three- to six-fold and soreness lasted 4 days; oxygen uptake was 4-7% higher from immediately after to 3 days after, with higher heart rate, ventilation, RER, perceived exertion, lactate and stride frequency and shorter strides with less ankle and knee motion.

The authors attribute the poorer economy to changes in running form and compromised muscle function.

Our reading: for a runner new to descents, a big downhill session shadows hard running for 2-5 days, while easy running below the lactate threshold is spared — the strongest case in this batch for a gap of several days before hard running after a first downhill block (still changed at day 5).

Protocol

2009 — participants: n = 15 untrained young men; age and VO2max not in the abstract. Familiarity: untrained; the downhill run was a first exposure (inferred from "untrained").
2009 — damaging session: 30 min of downhill running at −16% at the speed of the pre-determined 70% VO2max.
2009 — tests: level running at 70, 80 and 90% VO2max, 5 min each, before and 2 and 5 days after; oxygen uptake, minute ventilation, RER, heart rate, RPE, blood lactate, and stride length and frequency by high-speed video. Markers: maximal isometric knee-extensor strength, soreness, plasma CK and myoglobin.
2007 companion — participants: n = 10 young men (training status not stated). Session: 30 min at −15% at 70% VO2peak. Tests: level running at 65, 75 and 85% VO2peak, 5 min each, before, immediately after and 1-5 days after; the same physiological measures plus ankle, knee and hip range of motion (120-Hz video).
Time points: 2009 — 2 and 5 days (48 h and 120 h); 2007 — immediately and daily to 5 days (24 h to 120 h).
Funding and interests: not stated in the 2009 abstract or PubMed record; the 2007 paper is indexed in PubMed as "Research Support, Non-U.S. Gov't" and OpenAlex lists the National Science Council (Taiwan) as funder. Printed statements could not be read.

Key Results

2009 — change from baseline after a 30-min −16% downhill run (abstract):

Level-running intensity2 days (48 h)5 days (120 h)
70% VO2maxno significant changeno significant change
80% VO2maxall economy and kinematic measures changed (P < 0.05)changed (P < 0.05)
90% VO2maxchanged (P < 0.05)changed (P < 0.05)
Markers — knee-extensor strength down, soreness, CK and myoglobin uppresentstill present (lasting 5 days)

2007 companion — after a 30-min −15% downhill run (abstract):

MeasureResultDuration
Oxygen uptake during level running (stages at 65, 75 and 85% VO2peak; per-stage results not given)+4 to 7% (P < 0.05)immediately to 3 days
Heart rate, ventilation, RER, RPE, lactate, stride frequencyincreasednot given per variable
Stride length, ankle and knee range of motionreducednot given per variable
Markers — knee-extensor strength−7 to −21% (P < 0.05)soreness 4 days
Markers — CK and myoglobinthree- to six-fold increase—
Neither abstract gives the size of the 2009 economy change, confidence intervals or individual responses; the 2007 abstract does not say whether the 65% stage changed, so the two abstracts cannot be compared at easy intensity.

Mechanisms

Measured: economy changed together with stride length and frequency and with joint range of motion; the changes appeared at 80-90% of VO2max but not at 70% (2009).
Authors' interpretation: altered running form and compromised muscle function from damage reduce economy, and economy tested at a high intensity is affected more than below the lactate threshold.
Inference: damaged muscle costs most when force per stride is high, so a recovery jog shows little while a threshold or interval session meets the full cost.

Practical Application

How long after a first big downhill run before hard running? In untrained men, running economy at 80-90% VO2max was still worse 2 and 5 days after 30 min of steep downhill; at 70% it was not. Probably a first exposure (B).
After a first or unusually long descent, keep threshold and interval running away for days, not a fixed 72 h (economy at 80-90% VO2max was still changed at day 5 in 2009; no tested time point was clean). Not from this paper; the base's own practice: graded downhill exposure finished before the taper, and not a first downhill block inside the last ~10 days before a race (SYNTH-61).
Easy running looks cheap in the damage window — economy at 70% of VO2max showed no significant change at 2 and 5 days (2009), though the 2007 abstract reports oxygen uptake 4-7% higher for 3 days without saying whether its 65% stage was spared.
Accustom the legs first. These were untrained men on a −15 to −16% slope for 30 min; graded downhill exposure reduces the damage of the next bout (REF-660, REF-549). Not from this paper; the base's own practice: a slower build of downhill work for a runner new to descending (SYNTH-61).

Limitations

Read from the abstracts only; magnitudes at each intensity (2009), the per-intensity results (2007), participant characteristics and individual responses could not be checked.
Untrained or unspecified young men, a first exposure to a steep 30-min descent; trained or descent-accustomed runners will show less.
No control group; no time-trial outcome; economy measured in 5-min stages.
The 2009 abstract says the markers lasted 5 days; the 2007 abstract gives oxygen-cost changes for 3 days and soreness for 4 — consistent in direction, different in reported duration.
Funding: 2007, National Science Council (Taiwan) per OpenAlex; 2009 not stated; conflicts not stated.
How this entry was checked and changed
Why this level

uncontrolled pre-post, n = 15 (2009) and n = 10 (2007), the rubric's B band; the outcome is running economy, a determinant of performance rather than performance, in untrained men; read from the abstracts (both full texts are closed and the Edith Cowan University records listed by OpenAlex are metadata only)