REF-235 · Nieman et al., 2014 · Brain, Behavior, and Immunity, Vol. 39, pp. 180-185 · Paper · PubMed
Immune and inflammation responses to a 3-day period of intensified running versus cycling
Participants
n=35: 13 trained long-distance runners (age 34.4 ± 2.4 yr) + 22 trained cyclists (age 36.6 ± 1.7 yr; P=0.452 for age)
Protocol
Exercise: 2.5 h/day for 3 consecutive days at 70% VO2max (running or cycling), in the lab during week five of the monitoring period
Blood samples: before and after the 3-day block, and at 1 h, 14 h and 38 h of recovery
Assays: muscle damage (CK, myoglobin), inflammation (CRP, IL-6, IL-8, IL-10, MCP), innate immunity (granulocyte and monocyte phagocytosis and oxidative burst)
URTI monitoring: Wisconsin Upper Respiratory Symptom Survey (WURSS) for 12 weeks
Key Results
| Parameter | Runners vs Cyclists (post 3-day block) |
|---|---|
| Creatine kinase (CK) | 133% higher in runners |
| Myoglobin (MYO) | 404% higher in runners |
| C-reactive protein (CRP) | 87% higher in runners |
| Interleukin-6 (IL-6) | 256% higher in runners |
| IL-8 | 61% higher in runners |
| IL-10 | 32% higher in runners |
| MCP (monocyte chemoattractant protein) | 29% higher in runners |
| DOMS (delayed onset muscle soreness) | 87% higher in runners |
| Granulocyte/monocyte phagocytosis | Significant downturns by 14 h and 38 h recovery, pattern not different between groups |
| Granulocyte/monocyte oxidative burst | Significant downturns by 14 h and 38 h recovery, pattern not different between groups |
| 12-week URTI severity | No difference (runners 18.3 ± 5.6 vs cyclists 16.6 ± 4.0, P=0.803) |
| 12-week URTI symptom score | No difference (runners 33.4 ± 12.6 vs cyclists 24.7 ± 5.8, P=0.477) |
Mechanism
Inference, not tested in this study: running's ground-impact (eccentric) loading is the usual explanation for the far greater muscle damage and the larger systemic inflammatory response (CK, MYO, IL-6, CRP), while cycling is predominantly concentric. What the data do show: the innate-immune downturn (phagocytosis, oxidative burst) and the 12-week URTI symptomatology were the same in both groups, so the immune cost of the 3-day block did not track the muscle damage.
Practical Application
After 3 days × 2.5 h at 70% VO2max, 13 trained runners had 133% higher CK, 404% higher myoglobin, 256% higher IL-6, 87% higher CRP and 87% more soreness than 22 trained cyclists — yet the post-exercise fall in innate immune function and the 12-week URTI symptom scores did not differ between the sports. For a cyclist, a functional-overreaching block costs far less muscle damage and inflammation than the same block of running would, but no less immune vulnerability.
Running block planning: Inference, not tested: three consecutive days of intensified running create a large inflammatory load; the study's recovery samples ran to 38 h, so how long soreness and CK take to normalise beyond that is not shown here. Not from this paper; the base's own practice: allow 48-72 h of easy training after such a block.
Overreaching blocks: Inference, not tested: cycling tolerates a higher frequency of long days before muscle damage becomes limiting — the study compares one 3-day block, not progressive volumes.
URTI risk: both modalities suppressed innate immunity equally at 70% VO2max, and infection symptoms over 12 weeks did not differ — the "open window" followed the metabolic load, not the modality. Not from this paper; the base's own practice: guard the immune window with sleep and fuelling rather than by choosing the sport.
Limitations
Unequal group sizes (n=13 vs n=22) and allocation by sport, not randomization; trained but not elite athletes; single intensity (70% VO2max) — responses may differ at threshold or supra-threshold; no dietary standardization reported in the abstract; running group inherently self-selected for eccentric tolerance.
How this entry was checked and changed
Content correction 2026-09-27
Tier line said Tier 4-5 (Elite/International) -> the abstract says "trained" runners and cyclists and the Limitations already said "trained but not elite"; now Tier 2-3.
Mechanism (eccentric loading, "immune suppression driven by metabolic stress") -> labelled inference; "plan 48-72 h recovery", "nutrition and sleep matter more" -> labelled house practice. Type line notes allocation by sport, not randomization.
Cross-reference descriptions checked against the cited entries' current content; wrong years, wrong entries and claims the cited entry does not make were corrected.