Hemolytic Anemia from Footstrikes – A Runner’s Perspective


Mechanical Hemolytic Anemia + How it Affect Runners

The main source of runner’s anemia is foot strike impact which can trigger mechanical hemolytic anemia in athletes.  It is this force, according to the Journal of Applied Physiology, initiates a cascade of events that cause  your red blood cells to burst. This was first recorded in 1861 by an Army physician observing a soldier who just completed arduous and demanding field marches. The soldier was suffering from foot strike anemia. Hence, we have one of the many names for runner’s anemia, March Hemoglobinuria. Runners are not alone. This condition is also reported in tennis, basketball, weightlifters,  conga drum players, bicyclists, rowers, cyclists, ballet dancers, hand strengthening exercises, and in people after beating their head against a wall!




The rupturing process is called hemolysis; the words hemo is the meaning for blood and lysis is the meaning for breakdown. As the dying process of hemolysis continues the red blood cell count diminishes, which affects overall health, performance, stamina, quality of life and sports enjoyment.  This condition is described by many names.

Mechanical Hemolytic Anemia caused by footstrikes may also be referred to as:
  • Exercise-induced hemolysis
  • Exertional hemolysis
  • Foot strike anemia
  • Foot strike hemolysis
  • Hemolytic anemia
  • Intravascular hemolysis
  • Runner’s anemia
  • March hemoglobinuria (yes, are in marching)
  • Mechanical hemolytic anemia
  • Microangiopathic hemolytic anemia
  • Sports anemia

In any given one mile of running, your foot strikes the ground at full impact and intensity about 1600 times. The combination of continual, repetitive contact of your foot to the earth surface, coupled with the shock forces radiating upwards on the lower extremities, and any body equipment protection all play significant roles in exposure, risks, and injuries.

For more than 80 years, there are many literature reports of red blood cell hemolysis from numerous types of sports, exercise, and demanding elite activities. Most notably long-distance track runners who reported blood in their urine after racing.  Exercise-induced hemolysis, specifically from long distance and marathon running is connected to higher rates of red blood cell death.  The footstrike trauma from running is a key consideration of hemolysis.




What is Hemolytic Anemia?

Let’s start with some straightforward terms, biology, and the inner working structures.  Oxygen is one component of the air we breathe. It is literally the life blood of the human body (pun intended). Whole blood is made up of several elements:

  • White blood cells (WBC) or leukocytes make up about 1% of our blood and their life span is about one to three days.  They support our immune system as warriors in the first line of defense against invading infectious microorganisms. White blood cells are produced in the bone marrow at a rate of approximately 100 billion per day.


  • Plasma makes up 55% of our blood volume and consists of 92% water with additional proteins, lipids, and hormones. Plasma is the fluid transportation network. Its function is to move molecules and nutrients in and out of the system. By bringing nourishment, water, hormones, medications, proteins to your cells throughout the body, the tissues grow, work, and behave appropriately. Plasma is also the sanitation scavenger. It removes cell and tissue byproducts, waste, and discarded particles. In addition to supplying nutrition and elimination, plasma maintains your blood pressure.


  • Platelets make up less than 1% of our blood and have a life span range of nine to 12 days. They are your internal and external first aid, Band-Aid, produced by the bone marrow.  When we bleed, platelets circulating in the blood stream are activated and arrive quickly at the scene. They begin the clotting process in about 12 -15 seconds to stop the bleeding. They are your plugs.


  • Red blood cells (RBC) make up about 44 % of our blood and last about 120 days. They travel from the lungs in our respiratory system to all parts of the body. Red blood cells carry oxygen and remove carbon dioxide. The body produces 200 billion red blood cells per day.




Red blood cells are also called erythrocytes. The word comes from the Greek, erythros meaning red and kytos for a hollow vessel. The primary mission of red blood cells is to carry oxygen from the lungs in your respiratory system to every bodily organ, tissue, and cell. On the return trip, they take carbon dioxide from the cells back to the lungs, which we breathe out.

Inside red blood cells is an iron-containing protein called hemoglobin. Hemoglobin is the conveyor belt that transfers oxygen to waiting cells. When a red blood cell breaks apart, the hemoglobin goes directly into the blood stream and reduces the quantity of oxygen available that makes it to the tissue cells for absorption.

Hemolytic anemia happens when the rate at which red blood cells rupture and die is faster than the rate they are born from the bone marrow.  This situation also happens when red blood cells are removed by the spleen.  This supply and demand become unbalanced.

Recurrent traumatic force impacts brought on by physical activities such as cycling, weightlifting, rowing, biking, swimming, jogging, and long distance marching and running are a few examples that can cause red blood cells to rupture. If the body offsets the loss then the cost is mild. Sometimes, the body is unable to correct quickly enough resulting in low levels of hemoglobin and iron. The reduction of hemoglobin is called anemia.




In the investigation, entitled ‘Footstrike is the major cause of hemolysis during running’, published in the Journal of Applied Physiology the medical team of R. D. Telford, G. J. Sly, A. G. Hahn, R. B. Cunningham, C. Bryant, J. A. Smith looked at the influence of running and cycling on the destruction of red blood cells.

They took 10 male triathletes. Each person did two distinct sessions of one-hour of cycling and one-hour of running one week apart at equal peak oxygen uptake of 75%.  Doctors monitored the following substances for signs of hemolysis comparing the two sporting activities, running and cycling and their outcomes.

  • Plasma or serum free hemoglobin measures the amount of hemolysis for any given reason. Hemoglobin is found inside the red blood cells. Normal plasma does not contain free floating hemoglobin levels. Its presence in the blood stream  indicates red blood cell rupture.
  • Serum haptoglobin concentrations decrease as the extent of hemolytic anemia increases. Haptoglobin attaches to free plasma hemoglobin letting natural breakdown occur. Low levels of haptoglobin indicate hemolysis of red blood cells.
  • Methemoglobin is a generic and general measure of trauma to the circulatory system and red blood cell stress. A high level indicates the reduction of oxygen to the tissue cells that can result in neurologic and cardiac symptoms as the tissues are starving for oxygen.

The study results showed that both running and cycling increased plasma free hemoglobin; however, in the running component there was a fourfold greater increase in plasma free hemoglobin.  From cycling, there was no meaningful change to the haptoglobin levels. Yet, there was an important reduction after running.  Methemoglobin, the general stressor measurement, showed a twofold elevation. This happened after running and cycling, meaning that both activities reduced the oxygen supply to the tissues. There was no significant difference in the amount of methemoglobin decline between the two exercises.

Overall, the study concluded, “The present data indicates that, whereas general circulatory trauma to the red blood cells associated with one hour of exercise at 75% maximal oxygen uptake may result in some exercise-induced hemolysis, footstrike is the major contributor to hemolysis during running.”

In addition, proof of exercise-induced hemolysis was found in sporting activities that do not have the foot impact motion. This suggests the need for self-monitoring, annual blood work, and risk reduction by athletic enthusiasts involved in hard training, strenuous physical activities as long-term performance can be affected.




Anyone can develop anemia; however, mechanical hemolytic anemia has a higher incidence in physically active people and athletes. It starts very slowly and is insidious. The signs and symptoms are so subtle that many people do not even know they have it or are at risk. The hints range from no signs or symptoms to non-descript and specific warnings that something is wrong.

Seek out medical care if you have unexplained indications which include the following:
  • Feeling tired, worn down and fatigued
  • Faintness, dizziness, lightheadedness, confusion
  • Sallow, pasty, pallor skin complexion
  • Weakness, shakiness, unsteady with reduced power and skill in the physical activity
  • Unexplained fever, infection
  • Blood in the urine or dark urine
  • Yellow shadow to the skin and whites of the eyes and developing jaundice
  • Increased heart rate, heart murmur, chest pain
  • Enlarged liver and/or spleen
If ignored or left untreated for a long period of time one can develop:
  • Anemia
  • Thrombosis or clots
  • Chronic kidney disease
  • Pulmonary hypertension
  • Organ damage
  • Reduced quality of life
  • Reduced performance

Gastrointestinal blood loss has been detected in about 20 percent of long-distance runners. This occurs from strenuous races accompanied by traumatic mechanical kidney or renal blood loss. These effects have not been observed in swimmers or bicyclists.

Early identification of Runner’s anemia is possible and treatable. Keep current with your yearly physical exam or doctor’s appointment. Be proactive with requesting a simple blood test which will spot changes in the blood well in advance, especially if you are a devoted, passionate runner or athlete.





The causes of hemolytic anemia are varied and dependent on age, overall health, hereditary, and environmental conditions. The origin of hemolytic anemia is divided into two categories.

One is called intrinsic hemolytic anemia, from the inside. These are conditions in which the body itself makes defective red blood cells.  The issue is innate or congenital, due to something within the organ or body itself, plainly meaning coming from the inside the system. Examples of intrinsic causes are:

  • Genetically inherited red blood cell disorders
  • Thalassemia
  • Sickle-cell anemia
  • Paroxysmal Nocturnal Hemoglobinuria
  • G6PD deficiency of a red blood cell enzyme
  • Hereditary spherocytosis

The other category is extrinsic hemolytic anemia, from the external environment. These are conditions come from the outside of the body where red blood cells are mechanically or biologically destroyed or damaged in the circulation. The types are usually immune or drug related and other triggers.

Some examples of extrinsic causes are:
  • Auto-immune diseases such as rheumatoid arthritis, systemic lupus erythematosus, and chronic lymphocytic leukemia
  • Infectious hemolysis from gram positive bacteria such as Streptococcus, Enterocuccus, and Staphylococcus
  • Parasitic hemolysis from Plasmodium and malaria
  • Medication drug-induced hemolysis some examples include acetaminophen (Tylenol), penicillin (Pen VK), ampicillin, methicillin, chlorpromazine (Thorazine), ibuprofen (Motrin), interferon alpha, procainamide, quinine, and rifampin (Rifadin)
  • Mechanical trauma destruction hemolysis
  • Prosthetic heart valve replacement surgery
  • Cardiopulmonary bypass surgery
  • Paroxysmal nocturnal hemoglobinuria (PNH) which in very rare and life-threatening disease of the blood.
  • ABO mismatches blood transfusion reaction where you receive the wrong type blood in a blood as a transfusion. The body’s immune system makes antibodies that quickly kill red blood cells.





  • Snake or insect bites
  • Nutritional deficiencies such as Vitamin B12, Vitamin E
  • Lead poisoning, burns
  • Tumors, Lymphoma
  • Myelodysplastic syndrome
  • Microangiopathic hemolytic anemia
  • Pyruvate kinase deficiency


Risk Factors

While there are many risk factors for hemolytic anemia mentioned above, Runner’s anemia has relatively few. In addition, these can be minimized or eliminated with proactive thought and equipment. Here are some pearls to consider in diminishing the risks.

Risk Factors

Check the hardness of the running surface. Solid, resistant, rigid pavement contributes to foot strike anemia and addition risks of injury with each pounding stride. Wear great shoes that have firm, hard insoles with soft linings and cushioning.

Establish some precautions if you are a long-distance runner, aerobic dancer, triathlete or elite athlete by limiting the length, intensity, and frequency of the sessions. Lower levels of oxygen in the blood can lead to rising levels of lactic acid resulting in accumulation and longer recovery times.

Depending on the frequency of your workouts, a single sport exercise may not lead to anemia; however, daily or twice daily incidents of hemolysis can cause iron deficiency. This, in turn, can affect sports activity performance.

Key Pearls to Minimize Risks
  • Running surface hardness and flexibility
  • Running shoes support, soft linings, hard insoles, and cushioning
  • Watch length, intensity, consecutive, session frequency
  • Keep current with health care providers annual check up exam





March hemoglobinuria, sports anemia, traumatic hemolysis, foot strike impacts and blood loss play a role in the differential diagnosis. There are several things your doctor or health care provider will do to diagnose footstrike mechanical hemolytic anemia; however, the primary diagnostic method is blood tests.

Physical Exam

Upon physical exam, your doctor will look for a change in skin pallor and eyes. They will palpate and examine the stomach and abdominal areas. This will help in detecting tenderness and enlarged organs such as your liver and spleen.

Blood Tests

The doctor will order an analysis of a blood sample. Within that sample there are several substances that will be checked.

  • The total amount of red blood cells count, if lowered will indicate loss of blood.
  • Serum haptoglobin levels look for the amount or red blood cells in the body.
  • The urinalysis will look for blood in the urine, especially within hours of days or of exercise.
  • Reticulocytes are young, developing red blood cells. Looking at this count determine how many red blood cells your body is making. A higher count indicates more are being manufactured to fill a need.
  • Liver function tests will check the overall health of your liver. The accompanying bilirubin will measure the amount of red blood cells the liver has broken down.
  • Iron and ferritin levels may be ordered to rule out iron deficiency anemia.
  • Microscopic view of the blood might be performed to confirm correct size and shape.
  • Rarely is a bone marrow aspiration or biopsy completed. This provides information as to how many red blood cells are being made and their shape.
Erythropoietin (EPO) Oxygen Doping

In some sports sectors, there is extensive and well-known use of erythropoietin (EPO) doping among athletes and competitors. Erythropoietin is a natural hormonal protein our bodies release from the kidneys. This hormone activates bone marrow to make more red blood cells. An increase in red blood cells brings more oxygen to tissues, organs, and cells.

The prescription medication of erythropoietin is called epoetin alfa (Epogen or Procrit). It is given as an injection into a vein or under the skin. Epoetin alfa is approved for use in people who have kidney disease and require dialysis. The agent treats and prevents chronic renal failure anemia.

Blood erythropoietin doping is hard to detect. A red flag possibly indicating misuse is a high hematocrit level. Exercise, training, and working out would cause the hematocrit to be lower. Everything has side effects and a risk. Many of the risks are unknown and will not be knowable until sometime in the future. The bottom line is a personal ethic to the sport and maintaining your health, now and long-term.





Unless intense, frequent, and severe over a long period of time, footstrike hemolysis will not negatively affect your health. Treatments differ based on the cause of hemolysis, severity, your age, health, and tolerance to medications.

Mild cases will resolve on their own with time, rest, and recovery. For most runners and athletes, the reduction of physical activities involved with the rest and recovery part is the most difficult. Take a well-deserved time out and try another sporting avenue. If not and you are a long distance running athlete who develops a serious case here is a pearl for consideration. While it is recommended that a rest period be taken from intense exercise, some people prefer to start cross-training. This is a great way to try another sport. Either way it is curable with rest, recovery, and treatment.



Changes in diet or taking medications are not necessary. In rare, but critical conditions a blood transfusion may be needed. This method will quickly increase red blood cells and oxygen supply by direct replacement. In the most serious cases where the spleen is found to be destroying red blood cells, surgery may be required to remove the spleen.


All medications have risks, benefits, and side effects. Consult your health care provider before starting anything new.

Some medications used in treatment of severe conditions include:
  • Immunoglobulin that enhances the function of the immune system.
  • Corticosteroids that block the body from making antibodies that destroy red blood cells.

A non-drug way to limit, prevent, and treat this condition is look at your shoes! You have invested a lot of time, sweat, coaching, training, and devotion to your chosen sport. Great footwear combined with insole hardness reduces impact forces. Studies have repeatedly shown that the hardness of the shoes insoles is a successful technique in reducing the amount of hemolysis when compared to soft insoles.



See them here: (Insoles for FootStrikes)


Red blood cells require iron to perform optimally. Every day we lose one to two milligrams as a normal part of body processes. This amount is easily absorbed from the small intestine and replaced by the foods we eat. However, is some instances your health care provider may recommend an iron sulfate or iron gluconate replacement vitamin. These can be purchased without a prescription. Check with your doctor for your individualized dosing and length of therapy. Oral iron supplements can cause gastrointestinal upset, constipation, nausea, vomiting, abdominal discomfort, and dark tarry looking stools. Blood tests will been to be performed to make sure the iron and/or ferritin levels have returned to normal ranges.

Iron loss in sports activities and exercise is cumulative. This can occur in athletes who join in other physical trainings, such as tennis and basketball players, weightlifters, cyclists, and ballet dancers. It comes chiefly from the number of consecutive training sessions, degrees and intensity of hemolysis, perspiration, gastrointestinal bleeding, and hematuria (blood in the urine).

When the condition of iron deficiency anemia is diagnosed, your doctor will prescribe the appropriate type and dose of iron replacement therapy for you. The incidence of iron deficiency anemia increases in people who follow a vegetarian diets, young-adolescent, and females who are menstruating.

While iron does have a relevant function in an athlete’s performance, do not start any iron supplementation without seeking medical advice from a health care provider. Taking too much iron can harm the heart and liver, and may result in a condition called hemochromatosis.

Summary Checklist of What to Expect in Treatment:
  1. Make and keep your doctors appointment.
  2. Physical exam
  3. Blood work
  4. Urine tests
  5. Possible medications (iron supplement, immunoglobulin, corticosteroids)
  6. Sport equipment (firm, hard insoles, soft lining and supportive structure)




According to the Journal of Sports Medicine, Arthroscopy, Rehabilitation, Therapy and Technology, firm, hard insoles successfully reduce hemolysis in runners.  Shock absorbing insoles limit the intensity, amount and size of impact forces caused at foot strike. This is in addition the selection of soft running paths and cushioned well supported running shoes.


Example of a highly cushioned, well supported shoe


See more here: (Highly Cushioned Running Shoes)


A study compared soft and firm insoles on the development of runner’s hemolysis. In the group of athletes using soft insoles with less cushioning, there was a significant increase hemolysis. The softer the insoles the higher the rate of red blood cell rupture. Conversely, the group that used hard, firm insoles showed less hemolysis as the equipment successfully limited the foot impact intensity.

Here are some proactive preventative measures you can take to minimize any risk or cumulative harm. These involve the following:
  • Watch and replace your running shoes consistently. It is not in your best interest to completely wear out your running shoes before investing in another good pair.
  • Wear hard, firm insoles with shock absorbers with soft shoe linings. This will lessen and limit the impact forces that radiate up the lower extremities with each step. It is important to realize that even with better designed footwear, padded, firm insoles there will be some hemolysis just from the pressures of walking and running.
  • Locate and run on softer surfaces, if possible as this will augment the cushioning effect of the equipment. Runners who were encouraged to modify their gait and running technique found a reduced level of hemolysis.




False Positives

In the case you may not be aware, a test result that shows a condition that does not exist is called a false positive. A false positive is an error and mistaken result. It is important during diagnosis that multiple and varied markers are tested and verified. Experienced clinicians and laboratories will double check conclusions. There are several instances where a screening can result in an incorrect finding.

They include:
  • Toxins that include arsenic, metals, copper, nickel, lead, chromium/chromates, and platinum
  • Hepatitis infections
  • Systemic Lupus Erythematosus
  • Epstein-Barr Virus
  • Typhoid fever
  • Sickle cell anemia
  • Leukemia
  • Lymphoma
  • Tumors and types of cancers
  • Penicillin, pain medication, Dapsone, quinine, nitrites, nitrofurantoin
  • Streptococcus infection
  • Wiskott-Aldrich syndrome
One must also take into account associated and related problems consisting of:
  • Blood in the urine, hemoglobinuria
  • Low iron in the red blood cells, iron deficiency anemia
  • Preexisting medical disorders






The literature supports that red blood cell hemolysis happens from many sports, exercises, and physical activities.

The condition accepted as foot strike mechanical hemolysis or exertional hemolysis is caused by repeated trauma to the soles of the feet upon hitting the pavement. Associated with the destruction of red blood cells, the sustained chronic impact has shown influences on red blood cell loss, iron deficiency anemia, and hematuria.

A runners or athletes’ iron deficiency stage can keep them from optimizing aerobic strength and dampen their performance.

There are important health issues that accompany iron deficiency and iron deficiency anemia, in both males and females. With monitoring,  treatment, and stable follow-up proactive measures can be taken. By selecting a firm, hard insoles, cushioned shoes, competitors, and trainers can lessen or negate red blood cell hemolysis.

The training for any sport is a devotion. You train hard, use the best equipment, and balance it all with healthy dietary choices and supplements.

If you find yourself beginning to have to work harder and make more of an effort than before, it is time for a physical check up. Unexplained tiredness, fatigue and sleeping difficulties are not the norm.

Trace elements such as iron in the blood keep the body function to peak performance.

It is responsible for maintaining your immune system and energy production structures. Carrying oxygen to starved tissues, is a huge task when the intense exercise workload is large. Muscles, ligaments, brain, and heart all need oxygen while you are running the marathon.

Staying healthy means listening to your body.

It means taking the time to make appointments and follow up with physical exams, blood and urine tests, and possible the pharmacy. It also means keeping your equipment up-to-date, stable, supportive, and not in tatters!

When it comes to running , physical activity, and sports, the season is always right no matter what time of year.

Be pre-emptive by seeking information and knowledge of all aspects of your sport. When taking the initiative to be safe and curtail injuries, you will continue to enjoy this sport, the comraderies, and thrive.


This material is not intended as a substitute as medical recommendations. It is supplied by RunnerClick as a guide to initiate questions and discussion with your health care provider. Make sure you discuss any questions you have with your health care provider as related to your unique, specific, individual conditions and concerns. This article used sound, credible references and they are listed below for your further investigations.


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