Running vs. Cycling: The Science Behind
The eternal debate among endurance athletes, particularly those who compete in triathlons, is whether cycling or running is tougher on the body. There are obviously a number of differences between the two activities. In particular, running is the more efficient of the two, but cycling is lower-impact and easier on the legs.
Exercise scientists and biologists from Appalachian State University, Shanghai University, and the University of North Carolina took the argument one step further by systematically examining the differences between eccentric exercise (i.e. running) and concentric exercise (cycling) during a period of functional overreaching. Athletes engaged in a 3-day period of higher-than-average training volume and intensity.
The results, which are published in Brain, Behavior, and Immunity1 looked at three major factors that affect endurance athletes: inflammation, muscle damage, and immune function. The scientists showed running results in the most muscle damage, soreness, and inflammation over a 3-day period of intense training, while immune function remained the same among both athletes.
The participants in this study included 13 highly-trained distance runners aged 19 – 45 (seven males, six females) and 22 cyclists (17 males, five females). Details pertaining to the physiology of each group of participants are shown in Table 1 of the study. Each participant agreed to train normally and maintain a healthy weight for the 12-week duration of the study while avoiding the use of supplements that may promote recovery. During Week 5 of the study, each participant completed a 3-day exercise program that involved 2.5 hours of treadmill running or stationary cycling at approximately 70% of VO2 max. Prior to exercise on Day 1 of the functional overreaching period, each athlete provided a blood sample. Subsequent blood draws were taken immediately following exercise on Day 3, as well as one, 14, and 38 hours later. Blood tests were designed to examine biomarkers for inflammation, muscle damage, and immune response.
Inflammation2 is a normal – and necessary – way for the body to fight oxidative stress due to heavy wear and tear on muscles during exercise. Recent studies on inflammation show as this phenomenon becomes chronic, the incidence of overtraining syndrome, injury, and illness are drastically increased. Inflammation can also occur outside of exercise, caused by too little rest, improper diet, or stress. Much effort has recently gone into understanding inflammation and athletes, as well as the development of ways to reduce inflammation for better recovery.
When it comes to running versus cycling, inflammation was shown to be higher among the runners during the functional overreaching portion of the experiment. One protein and four inflammatory cytokines were examined: c-reactive protein (CRP), monocyte chemoattractant protein- 1 (MCP), IL-6, IL-8, and IL-10. Figures 1a – 1e show that runners and cyclists had few variations in their basal inflammation levels prior to exercise based on the existence of these proteins in their blood plasma. However, after three days of high-volume exercise, the runners showed the greatest inflammatory response, especially in the time period immediately following exercise. CRP levels remained higher in runners, even 38 hours post-exercise, while cytokines decreased markedly after 14 hours.
What causes such a systemic increase in inflammation in runners versus cyclists? The prevailing hypothesis is that running is a higher-impact activity that leads to greater muscle damage (discussed below), which necessitates more of a pro/anti-inflammatory response from the body in order to mitigate damage. Previous studies3 into the difference between eccentric and concentric exercise have shown similar results.
Muscle Damage and Soreness
To assess muscle damage and soreness among the athletes, levels of serum myoglobin and creatine kinase were measured. Myoglobin is a protein that is prevalent in cardiac and skeletal muscles. When muscle becomes damaged, myoglobin is released into the blood stream, where it can then serve as a quantitative biomarker for the amount of damage sustained during exercise. Similarly, creatine kinase is an enzyme that is found in skeletal muscle that is released upon oxidative stress and can be easily detected in the blood.
Like inflammation levels, runners and cyclists both had similar serum myoglobin and creatine kinase levels prior to the three-day period of intense exercise, as shown in Figures 2a and 2b. However, post-exercise, both biomarkers increased significantly for the runners while little increase was observed in the cyclists. For runners, creatine kinase levels remained significantly elevated 38 hours post-exercise, while cyclists actually saw decreased levels in comparison to pre-exercise values. A similar trend was observed for serum myoglobin but to a lesser degree.
Soreness, particularly delayed-onset muscle soreness (DOMS), was measured via subjective ratings of pain level from 1 – 10 by the participants. Soreness has been shown to correlate strongly4 with creatine kinase levels in the blood, and indeed that trend was observed in these studies. Prior to exercise, runners reported an average level of soreness just above a “2” on the pain scale, while cyclists were slightly below “2” (see Figure 3).
Immediately following the third day of exercise, runners reported feeling a soreness of “7,” while cyclists reported approximately half the amount of soreness, at “3.5”. Interestingly, runners continued to feel more soreness than cyclists up to 38 hours post-exercise, where cyclists reported being slightly more sore than their counterparts (approximately “2.3” vs. “2.4”).
Soreness and muscle damage are directly related to the level of impact of the two activities. The repetitive pounding of the runners versus the low-impact movements of the cyclists correlate to the amount of muscle damage, and therefore soreness, experienced.
Athletes who partake in high-level training are often at an increased risk of developing upper respiratory infections and illness thanks to the role that inflammation and stress play on the immune system. Immune function was examined both subjectively and objectively. From an objective perspective, the ability of the immune system to fight off bacteria, in this case Staphylococcus aureus, was measured using fluorescence labeling. Oxidative burst tests were also performed.
Surprisingly, runners and cyclists had similar immune function despite the fact that runners experienced more inflammation and muscle damage. As shown in Table 2, few significant differences were recorded in both phagocytosis and oxidative burst activity, indicating that immune function was similar among athletes. As predicted, immune function decreased immediately following the third day of intense exercise, but within 14 hours had returned to pre-exercise levels.
A second measure of immune function was taken subjectively via surveys conducted throughout the experiment. The Wisconsin Upper Respiratory Symptom Survey5, which includes 10 questions assessing various symptoms of upper respiratory disease (i.e. congestion, cough, fatigue, etc.), nine questions assessing functional impairments (i.e. ability to think clearly, breath easily, etc.), and one question to assess the global severity (i.e. mild to severe symptoms) was used.
Throughout the study, upper respiratory tract infection scores did not differ significantly among runners and cyclists, although runners did not consistently have slightly higher scores for severity and symptoms. This finding is consistent with the lack of innate differences between the athletes’ immune functions, as measured via phagocytosis and oxidative burst tests.
Critiques of the Study
As with any scientific study, there will be drawbacks in the methods used or in the experimental design. Although this study was comprehensive and filled gaps that previous, similar studies may have left open, it is not without criticism. One issue, from a scientific perspective, is that sample size was exceedingly small. With only 13 runners and 22 cyclists, there is certainly room for more participation in order to improve the statistical measurements.
Additionally biochemical measurements6 among both male and female endurance athletes are sometimes invalid, and should not always be treated as though they are equal. Scientific literature has proven that men and women produce inflammation7 in their bodies differently, which may affect athletic training in unique ways. While the authors do indicate that ANOVA calculations reveal no significant differences among men and women, it would be beneficial to look at each gender individually.
Finally, an overarching issue with this study is that it neglects the fact that VO2 max changes over time with fitness. Each athlete had his or her VO2 max tested at the start of the 12-week study. However, assuming that each athlete was in a varying state of fitness, VO2 max could have increased or decreased in five week’s time.
Therefore, exercising for 2.5 hours for three days in a row at 70% VO2 max may not have been as equal of an exercise among participants as the researchers had intended. Although the effect, in theory, should be negligible, the small sample sizes incorporated in this study indicate that even a small change in fitness could skew the results.
Overall, this study showed that when training load is increased for functional overreaching, runners (or triathletes) should be aware that inflammation and muscle damage will occur at a greater rate than is experienced by cyclists. While cyclists can build heavy periods of training into their regimes, runners should be careful to balance heavy and light workloads in order to minimize the damage caused by stress.
1. Nieman DC, Luo B, Dréau D et al (2014). Immune and inflammation responses to a 3-day period of intensified running versus cycling. Brain Behav Immun 39:180–185. doi:10.1016/j.bbi.2013.09.004 Link
2. Neubauer, O., König, D. & Wagner, K. Eur J Appl Physiol (2008) 104: 417. doi:10.1007/s00421-008-0787-6 Link
3. Margaritelis N. V., Theodorou A. A., Baltzopoulos V., Maganaris C. N., Paschalis V., Kyparos A., Nikolaidis M. G.. Muscle damage and inflammation after eccentric exercise: can the repeated bout effect be removed? Physiol Rep, 3 (12), 2015, e12648, doi: 10.14814/phy2.12648 Link
4. P. M. Clarkson, W. C. Byrnes, K. M. McCormick, L. P. Turcotte, J. S. White. Muscle Soreness and Serum Creatine Kinase Activity Following Isometric, Eccentric, and Concentric Exercise. Int J Sports Med 1986; 07(3): 152-155. DOI: 10.1055/s-2008-1025753 Link
5. Barrett B, Brown R, Mundt M, Safdar N, Dye L, Maberry R, Alt J., The Wisconsin Upper Respiratory Symptom Survey is responsive, reliable, and valid. J Clin Epidemiol. 2005 Jun;58(6):609-17. Link
6. Stephan van der Zwaard, Jo C. de Ruiter, Dionne A. Noordhof. Maximal oxygen uptake is proportional to muscle fiber oxidative capacity, from chronic heart failure patients to professional cyclists. Journal of Applied Physiology Vol. 121 no. 3, 636-645 DOI: 10.1152/japplphysiol.00355.2016 Link
7. Georges J. A. Casimir, Jean Duchateau. Gender Differences in Inflammatory Processes Could Explain Poorer Prognosis for Males. doi: 10.1128/JCM.02096-10. J. Clin. Microbiol. January 2011 vol. 49 no. 1 478-479 Link