Injury-Free Running, Second Edition: Your Illustrated Guide to Biomechanics, Gait Analysis, and Injury Prevention

Since the first edition of this book was published in 2013, new techniques for treating and preventing injuries have been developed. More importantly, some amazing new research has proven that there actually is an ideal running form. While previous studies suggested that because runners who are forced to modify their self-selected stride length or cadence become less efficient, it was assumed that runners have an innate ability to choose the ideal running form that is just right for them. The latest research shows that the runners self-select the best running form theory just isn’t true.

In 2017, scientists from the UK (1) performed a detailed biomechanical and metabolic evaluation on nearly 100 recreational runners and proved that making very specific changes in running alignment can not only make you more efficient but also allow you to run faster. I personally feel that these modifications in running form will also decrease your overall risk of injury. For slower recreational runners trying to remain injury free, a 2019 study showed that switching to a running technique called ground running reduces impact intensity by 35% and decreases musculoskeletal loading by 34% (2). Interestingly, switching to ground running from conventional running increases the runners’ metabolic rate by 5%, confirming that ground running is an excellent way to both stay fit and avoid injury. Because it takes almost no training to convert from regular running to ground running, you can markedly reduce your risk of injury with little to no effort.

Because parts of this book are moderately technical, Chapter 1 reviews everything you need to know about anatomy, while Chapter 2 explains everything that happens in your body while you walk and run. The importance of storing energy in muscles and tendons, and returning it to them, is always emphasized. Chapter 3 discusses new tests you can do at home to determine your risk of injury, and reviews new techniques for improving tendon resiliency and muscle strength. Not only will the exercise routines outlined in this book help you run faster, but they should also help you avoid injury.

A completely new chapter has been added that explains how to perform an at-home gait analysis. Chapter 4 reviews every aspect of gait analysis, and will walk you through the steps necessary to develop the ideal running style based on your running speed. This is followed by Chapter 5, an updated chapter on running shoes, as over the last five years a range of innovative models have completely changed the industry. Inspired in part by the early minimalist shoes, running shoe manufacturers have developed a wide range of interesting models, from the maximalist Hokas to the ultrafast Nike Alphaflys, which are actually capable of storing and returning energy. You’ll learn that unless you’re planning on running a marathon in less than two hours, you don’t need to spend $250 on a pair of shoes to run fast and/or avoid injury. It turns out that comfort is the key to improving efficiency and remaining injury free.

The last chapter of this book, Chapter 6, has also been modified to reflect the latest research regarding injury prevention, and a few novel treatment protocols have been added. For example, a great study by Sullivan et al. on plantar fasciitis proved that weakness of the toe and peroneal muscles (also known as the peroneals or fibularis muscles) are key in the development of plantar fasciitis (3). Until this paper came out, no one had even considered that weakness in the peroneals played a role in the development of plantar fasciitis. Other interesting studies have demonstrated that runners with retropatellar disorders can get back to running sooner when foot exercises are included in their treatment protocols (4), and that strengthening the soleus may be the key to treating and preventing Achilles injuries. The section on stress fractures details the precise steps you can take to get back to running, and the latest nutritional information is reviewed. A few surprising studies have shown that too much vitamin D can actually weaken your bones (5), and that Keto diets can cause rapid reductions in bone density and should therefore be avoided (6).

It seems like in the last five years more than ever, sports medicine specialists are finally realizing that rather than prescribing nonsteroidal anti-inflammatories and injecting tendons with corticosteroids (which are worse than no treatment at all), the best way to improve performance and avoid injury is by increasing muscle and tendon resiliency, improving neuromotor coordination, finding the ideal running shoe, and developing the precise running form that matches your biomechanical needs. Unlike the elite and recreational runners of the 1980s and 1990s who were treated with medications and ineffective stretches, today’s runners have access to state-of-the-art information that, with a little bit of effort, can allow them to run faster and avoid injury for a long time to come.

References

We take it for granted but the process of running around on two legs is an extremely unusual way to get around. Of the more than 4,000 species of mammals on earth today, only one is upright while walking. Even Plato commented on the curious nature of our preferred form of locomotion by referring to humans as the only featherless bipeds (there weren’t many kangaroos in ancient Greece).

The reason that 99% of animals on this planet prefer using all four limbs while walking and running is that moving around on two legs presents an engineering conundrum: When the foot first hits the ground, the entire limb must be supple in order to absorb shock and accommodate discrepancies in terrain, while shortly thereafter, these same structures become rigid so they can tolerate the accelerative forces associated with propelling the body forward. This is in contrast to quadrupeds, which have the luxury of being able to absorb shock with their forelimbs while their hindlimbs serve to support and to accelerate (picture a cat jumping on and off a ledge).

Shock absorption is particularly important in marathon running, since the feet of long-distance runners contact the ground an average of 10,000 times per hour, absorbing between two and seven times their body weight with each strike. In the course of a marathon, this translates into a force of over 12 million pounds that must be dissipated by the body. Obviously, even a minor glitch in our shock absorption system will result in injury. To make matters worse, the forces associated with accelerating the body forward are even greater than the forces associated with initially contacting the ground.

To understand the complex structural interactions responsible for shock absorption and acceleration, it is important to understand exactly how our joints, muscles, tendons, ligaments, and bones interact while walking and running. Because most runners are not familiar with anatomy and clinical biomechanics, the following section will provide an illustrated review of all the major muscles, tendons, ligaments, and bones associated with running. This review goes down to the cellular level, as understanding how our tissues repair and remodel is the key to preventing injuries and maintaining peak performance (e.g., healthy muscles and tendons store and return energy to enhance efficiency and off load our bones). To make this section easier to understand, the Greek/Latin origins of the names of our muscles and bones are listed. You will see that early anatomists never wanted anatomy to be complicated, as almost all of our muscles and bones are named according to their shape: The piriformis muscle looks like a pear, while the navicular bone resembles a ship.

The anatomy section is followed with a review of the words used to describe three-dimensional motion. At first, terms like dorsiflexion and eversion may seem complicated, but after hearing them a few times, they will quickly become part of your vocabulary. Last but not least, the final portion of this chapter summarizes what each muscle does while we run and what can go wrong if the muscle is weak and/or tight. All of this information will be covered in greater detail in subsequent chapters.

Fig. 1.1. Muscle anatomy. If you take a cross-section of any muscle, you’ll see small compartments called fascicles. Fascicles are visible to the naked eye and can be seen when cutting a piece of steak. Fascicles in turn are subdivided into fibers, which are embedded in connective tissue called the perimysium. The perimysium is a type of dense connective fascia, which is loaded with a mixture of strong supportive collagen fibers and a stretchable protein called elastin. The cells inside the perimysium are fibroblasts (A), which repair and remodel damaged collagen and elastin fibers. The perimysium is the structure we try to lengthen when getting massages and/or performing foam rolling.

Attached to the sides of fibers are satellite cells, which rebuild muscle fibers damaged during exercise. As will be discussed briefly, special sensory cells called spindles are also attached to the sides of muscle fibers. Spindle cells tell our nervous system exactly how fast and how far each joint is moving, and that information is analyzed to calculate the metabolic cost of each running step and make changes to improve efficiency. Last but not least, fibers are subdivided into myofibrils, which are made of proteins called actin and myosin. These proteins are the motors that drive muscle contraction. New research shows that when muscles are exercised in their lengthened positions (as in the bottom of this illustration), satellite cells kick into gear to accelerate remodeling. This information has been used to design exercises to help improve running performance.

Fig. 1.2. Tendon anatomy. As with muscles, tendons are divided into fascicles, fibers, and fibrils, but unlike muscles, which are almost 80% water, tendons are made of strong parallel collagen fibers, containing very few blood vessels and hardly any water. The limited blood supply and reduced water content allow tendons to function like steel cables: Their parallel fibers of type I collagen can withstand large forces without the slightest damage.

*When a tendon is injured, small repair cells called tenocytes, located between collagen fibers, rebuild the collagen fibers.

Recent research shows there are two completely different types of tendon: energy-storing tendons and positional tendons. The positional tendons are located where high force output is needed, such as in the muscles of your hips and thighs. When exposed to a stretching force, the small fibers slide back and forth over one another, moving only a small distance. This action allows the force generated by the muscle to then be transferred directly through the tendon to the bone. In contrast, energy-storing tendons, which are located almost exclusively below the knee, are designed with their fascicles angled slightly to one another, allowing them to slide and rotate on one another, and lengthening as much as 11%. This sudden lengthening is extremely important for maintaining running efficiency, as the stretching tendon stores and returns free energy like a bouncing rubber ball.

The improved storage of energy in, and the return of energy to, the energy-storing tendons explains why the world’s fastest marathon runners have the longest Achilles tendons. Elasticity present in energy-storing tendons also prevents injury, as it dampens force that would otherwise go into the muscle. The weak link in the application of force from tendon to muscle is the muscle–tendon junction. This is the most common site of a muscle tear, as the interface between the muscle and the tendon frequently rips (A in inset). Just as strengthening muscles in their lengthened positions stimulates muscle repair, strengthening tendons while they are maintained in a stretched position enhances tendon flexibility. Maximizing tendon flexibility is vital for avoiding injury and preventing age-related decreases in running performance because as we age, tendons naturally stiffen, which can be avoided with specific exercises and proper nutrition.

Fig. 1.3. Ligament anatomy. While tendons connect muscles to bones, ligaments connect neighboring bones to one another. They are structured similarly to tendons, except they contain more blood vessels to enhance healing, and more elastin fibers to make them stretchable (arrow). Ligaments are not as strong as tendons, and the higher elastin content makes them prone to tearing. The good news is that because they contain more blood vessels, they typically heal pretty quickly (except the ACL and PCL, which are located inside the knee joint and contain fewer blood vessels). (ACL = anterior cruciate ligament; PCL = posterior cruciate ligament; LCL = lateral collateral ligament; MCL = medial collateral ligament.)

Fig. 1.4. Bone anatomy. Bone is comprised of two different types of bony tissue: cortical bone and medullary bone. Cortical bone is also referred to as compact bone, while medullary bone is also known as spongy bone. The basic functional unit of cortical bone is the osteon, and it contains small blood vessels running through its core. Sprinkled throughout the osteon are osteocytes, which are important in repairing and remodeling bone. Cortical bone, which is surrounded by the pain-sensitive periosteum, is extremely powerful and resists bending forces like a steel pipe. In contrast, spongy bone is softer and is loaded with small chambers that allow for the production of red blood cells.

The ratio of cortical to spongy bone is dependent upon the stresses applied to the bone: Bones that are exposed to high bending forces, such as the metatarsals of your forefoot, are made almost exclusively of cortical bone (A). In contrast, bones that absorb shock, such as your calcaneus (B), are made primarily of soft spongy bone, which allows them to expand and absorb shock like a cushion.

Fig. 1.5. Sensory nerves of muscles and skin. Attached to the sides of muscle fibers and surrounded by epimysium, muscle spindles tell your central nervous system exactly how rapidly your muscles are firing and what they are doing while you are running. Contracture in the perimysium can inhibit information from spindles, increasing the risk of injury. The skin on the bottom of your feet is also important for injury prevention. Special receptors called Meissner’s corpuscles and Merkel receptors provide information regarding the transfer of pressure along bottom of your foot. When too much pressure occurs in one area, the skin receptors fire and produce a reflex contraction of the specific muscles necessary to offload the region receiving excessive pressure. For example, if excessive pressure is centered beneath your forefoot, the skin receptors cause your toe muscles to pull down, thereby redistributing pressure over a broader area (inset). Interestingly, foot massage and mobilization have been shown to increase the sensitivity of sensory receptors in the bottom of your feet, which can improve performance and help prevent injury.

Fig. 1.6. Skeletal anatomy.

*The tarsals are all of the foot bones located behind the metatarsals: the calcaneus, talus, cuboid, navicular, and the cuneiforms. The word tarsals is Latin for flat surface.

Fig. 1.7. Muscle anatomy (front view).

Fig. 1.8. Muscles of the back. The iliocostalis and longissimus muscles are important while running, since they prevent excessive forward lean of the torso. Collectively, these muscles are referred to as the erector spinae (Latin for erect the spine). The quadratus lumborum and the multifidi are powerful stabilizers of the spine and are exercised while performing side and conventional planks.

Fig. 1.9. Core muscles. These important muscles wrap around the torso, connecting our rib cage to our pelvis. The force created by the internal oblique (IO), external oblique (EO), and transversus abdominis muscles (TA) gets transferred through the lumbodorsal fascia (LDF) to help stabilize the entire lower spine (A). Though rarely discussed, the pelvic floor (not shown) and diaphragm (B) are also important core muscles. The diaphragm fires with the transversus abdominis to help stabilize the core and plays an important role in running, particularly sprinting. (Muscle abbreviations: ES = erector spinae; Mu = multifidi; PS = psoas; QL = quadratus lumborum; RA = rectus abdominis [the six-pack muscle].)

Fig. 1.10. Muscle anatomy (side view).

Fig. 1.11. Muscle anatomy (back view).

Fig. 1.12. The iliotibial band (ITB) and the iliopsoas. The ITB behaves as a broad tendon that transfers the force generated in the gluteus maximus and tensor fascia latae muscles to the leg and thigh. It has multiple attachments to the femur and plays an important role in preventing the opposite side of your pelvis from dropping too much while you run. The iliopsoas is a powerful hip flexor, and because of its multiple attachments to the lumbar spine, the psoas acts as a spinal stabilizer.

Fig. 1.13. Muscles of the front of the thigh. The adductors consist of the adductor longus, adductor brevis, adductor magnus, gracilis, and pectineus. The vertical portion of the adductor magnus is also called the ischiofemoral portion, since it runs from the ischium of the pelvis to the lower portion of the femur. The quadriceps consist of four different muscles: vastus lateralis, vastus intermedius, vastus medialis, and rectus femoris. The vastus lateralis is by far the largest of these muscles and plays an important role in shock absorption while running. The rectus femoris is the only quadriceps muscle to cross the hip joint, and it is one of the few hip muscles to possess a tendon that rotates appreciably. The rotation of the rectus femoris tendon allows it to store energy while your leg is extended behind you, and return that energy in order to bring your swinging leg forward.

Located in the quadriceps tendon, the patella is the body’s largest sesamoid bone. Sesamoid bones are located inside various tendons all over the body, especially ones requiring high force output. They essentially act to pull the muscle’s tendon farther away from the joint’s axis of motion, thereby improving the mechanical efficiency of the muscle. Think about a doorknob: If a doorknob is located close to the hinge, it is difficult to open the door. However, as the doorknob moves farther away from the hinge, less force is required to open the door. That’s essentially what sesamoids do. Sesamoid is Latin for sesame seed.

Fig. 1.14. Muscles of the back of the thigh. The hamstrings are subdivided into the semimembranosus, semitendinosus, and biceps femoris (which contains a long head and a short head). Because it attaches so low on the femur, the vertical component of the adductor magnus behaves as a hamstring. The hip rotators are also important while running, as they prevent the entire lower limb from twisting inward too much.

Fig. 1.15. Muscles of the calf and arch. The flexor hallucis brevis is important, as it contains two small sesamoid bones, which often cause problems in runners. Weakness of the muscles of the arch is an extremely common cause of injury: Abductor hallucis weakness correlates with the development of bunions, while a weak flexor digitorum brevis is a common cause of plantar fasciitis. The tibialis posterior plays an important role in supporting the arch, as it possesses numerous attachment points to the center of the arch.

Fig. 1.16. To describe motion, the body is divided into three reference planes: sagittal, frontal, and transverse.

Fig. 1.17. Sagittal plane motion of the spine.

Fig. 1.18. Sagittal plane motion of the hip.

Fig. 1.19. Sagittal plane motion of the knee.

Fig. 1.20. Sagittal plane motion of the toes and ankles.

Fig. 1.21. Frontal plane motion of the hip.

Fig. 1.22. Fixed frontal plane positions of the knees.

Fig. 1.23. Transverse plane motion of the hips.

Fig. 1.24. Transverse plane motion of the forefeet.

Fig. 1.25. Pronation and supination occur in all planes and represent lowering and elevation of the arch, respectively.

In order to understand what it takes to be a great runner (and remain injury free), it’s important to understand exactly what’s going on while we’re upright and moving around. To accurately describe the various anatomical interactions occurring while we walk and run, researchers have come up with the term gait cycle. Traced back to the 13th-century Scandinavian word gata for road or path, one complete gait cycle consists of the anatomical interactions occurring from the moment the foot first contacts the ground until that same foot again makes ground contact with the next step.

The gait cycle consists of two distinct phases: stance phase, in which the foot is contacting the ground; and swing phase, in which the lower limb is swinging through the air preparing for the next impact (Fig. 2.1). Because of the complexity of stance phase motions, this portion of the gait cycle has been subdivided into contact, midstance, and propulsive periods. Although running is also divided into the same three periods, the increased speed and the need for a more forceful propulsive period changes the timing of the events: The contact and midstance periods are slightly shorter, and the propulsive period is longer (Fig. 2.2).

Fig. 2.1. Gait cycle of the right leg. Stance phase begins when the heel hits the ground and ends when the big toe leaves the ground. Swing phase continues until the heel again strikes the ground. Stance phase is subdivided into contact, midstance, and propulsive periods. Important components of the gait cycle are step length, stride length, and cadence. Step length refers to the distance covered between the right and left foot in a single step, while stride length refers to the distance covered by a single foot during the entire gait cycle; i.e., the distance covered during two steps. Cadence (or step frequency) is the number of times your feet make ground contact per minute. While walking, the typical person takes 115 steps per minute with an average stride length equal to 0.8 times body height.

Fig. 2.2. Stance phase while running. Although running is divided into the same phases as walking, there is tremendous variation in stride length and cadence depending upon running speed. While recreational runners have stride lengths of about 6½ feet (2 m) and cadences of 165 steps per minute, the world’s fastest marathon runners have stride lengths of more than 10 feet and cadences of around 200 steps per minute. In contrast, Usain Bolt set the world record in the 100-meter sprint by running with a stride length of 16 feet (4.8 m) and a cadence of 265 steps per minute!

The neurological mechanisms necessary to complete the gait cycle are unusual in that swing phase motions are reflexive and present at birth (e.g., an unbalanced toddler will immediately swing the lower extremity into a protected position), while movements associated with stance phase represent a learned process. This statement is supported with the clinical observation that children born without sight make no spontaneous attempts to stand up and walk on their own and will only do so when physically guided.

As soon as we become toddlers, we begin experimenting with a wide range of walking and running patterns, subconsciously analyzing the metabolic expense associated with each variation in gait. This is a time-consuming process, and perfecting the musculoskeletal interactions necessary to become metabolically efficient can take up to a decade to master. Even when adjusting for size differences, the average three year old consumes 33% more oxygen when traveling at a fixed speed than an adult. By the age of six, children continue to burn more calories while walking and running. Fortunately, by age 10, mechanical efficiency is equal to that of an adult, and after almost a decade of practice, children are finally efficient at getting around on two legs.

What is Perfect Running Form?

Despite the controversy among coaches as to what constitutes perfect running form (they’ll tell you to modify everything from the position of your wrist to the angle of your torso), the actual answer is pretty simple and can be traced back to a 1953 article published in the Journal of Bone and Joint Surgery (1). In this article, a team of orthopedic specialists conclude that in order to