Running shoes are an important though highly complex biomechanical necessity for every runner. Many studies have been conducted to understand the impact of running with or without shoes on the kinetics and the kinematics (together known as biomechanics) of running. These studies consider the in-shoe pressure sensors, pressure mats, three-dimensional motion analysis systems, and lightweight accelerometers and many more sophisticated technologies to study the modern shoe biomechanics.
To understand the effect of running shoes on a runner’s foot, we first need to understand the biomechanics of the foot as well as running, energy expenditure during run, forces that act on foot when you run, different foot strikes and much more. Only after that we would be able to comprehend the effect of different types of running shoe designs on our running economy as well as running-related injuries.
Before you read further, give a quick glance to my previous article where I explained what we mean by Running Biomechanics, what constitutes a good running form and much more.
Running Shoes Categories
Around 7-10 years back, the shoes were broadly classified based on the amount of foot control they offered. But innovation in shoe design continues to happen and now the companies have started altering the amount of cushioning in the shoes and have started offering minimalistic and maximal shoes. There are a vast number of running shoes available in the market today and sometimes it is overwhelming to decide which one to buy. They can be very broadly classified into the following categories:
Motion control running shoes
a) Provide high stability and durability.
b) Recommended for runners with low arches, flat feet and moderate to serious over-pronation, which is the excessive inward rolling of the foot following a foot strike.
c) Shoes available in the market in this category are – Hoka One One Arahi 4, Brooks Adrenaline GTS 20, the Mizuno Wave Alchemy 12.
Stability running shoes
a) Recommended for the runners with normal running gait, normal shaped feet (normal arch/neutral feet) and neutral pronators (the feet roll inward in an efficient way). This shoe supports your natural stride.
b) Shoes available in the market in this category are – Asics GT 2170, Brooks Ghost 13, Mizuno wave rider 24.
Cushioned Shoes or Neutral Padded Shoes
They are without a lot of corrective or supportive elements. They are recommended for runners with little to no pronation as they offer both shock absorption and protection with little to no extra support throughout the gait cycle. They can be further classified into Barefoot, Minimalist, and Maximalist running shoes depending upon the cushioning.
Offer low midsole height, low heel-toe/zero drop (less than 8mm), high flexibility, and lower weight, no-arch support, thin sole with no motion control.
Shoes available in this category are Saucony Kinvara 9.
They create an ultra-lightweight, ultra-flexible from heel to toe, barely-there barefoot experience with heal drop of 0mm and reduce energy wastage as there’s less weight to carry. There is minimum cushioning/stability, and the runners rely solely on the body’s natural shock absorbing mechanisms.
Shoes available in this category are – Ultra Minimal Vibram Five-Finger, Vivo barefoot.
They are also generally constructed with a low heel-toe drop but they contain substantially greater midsole cushioning from the forefoot to the rearfoot compared to a traditional shoe providing good shock absorption. They are heavier in weight.
Shoes available in this category are – Hoka One One Clifton 4, Sketchers Go run Ultra R, New Balance Fresh Foam 980 Boracay.
Now that we are clear about the running shoes categories, let’s dive into understanding how these running shoes alter biomechanical efficiency of running and some of their impact on the risk of running-related injuries.
Impact of running shoes on the Ground Reaction Forces (GRF)
As discussed in my previous article, the Ground Reaction Forces act on the body when the body reacts to the external environment. The GRF is basically the net effect of muscle action and the acceleration produced in the body (in proportion to gravity and relative mass) while running.
GRF has the following components:
Vertical: The parameters are peak impact and rate of increase of force. Cushions in the shoes absorbs the reaction forces to protect the musculoskeletal system.
Anterior-Posterior: The parameters are braking and propulsion. The friction introduced by shoe soles impact these parameters.
Medial lateral: The parameters are pronation and supination. Shoes change the distance between the point of application of GRF and ankle joint thereby controlling the foot movement.
Footwear basically introduces the adjustments in the movement of legs which effect the kinetics of running. Running shoes changes the knees and ankle joint angles which changes the muscle activity in the lower extremities.
Impact of shoes on foot motion and excessive pronation
Various biomechanical variables such as strike pattern, ground impact forces, foot posture or foot pronation have all been proposed as injury risk factors. Various footwear features such as cushioning, stability provided, and motion control systems have been designed to lessen these risk factors.
Many a times, the inward rolling when the foot hits the ground (also called pronation), can result in serious injury over time. Running shoes can also control the magnitude and/or rate of both foot motion (rate/amount of pronation) and impact loading by placing it at optimum orientation for force.
- Motion-control/high-stability shoes hold the foot firmly in place.
- Stability shoes offer some motion control but manage to provide more support, flexibility, and cushioning.
Following are the few conclusions from numerous research conducted on the effect of motion-control running shoes on injury risk.
The tibial rotation (twisting of the shinbone) is significantly reduced during running with motion-control shoes in comparison to neutral shoes. This reduction in tibial rotation has been linked to a reduced risk of running injury.
Runners have more stable activation of the quadriceps muscles, specifically the vastus medialis obliquus, and lower leg muscles which may reduce symptoms of Patellofemoral Pain Syndrome (PFPS). They tend to bring the lower limb back to more neutral skeletal alignment which assist the knee to follow a more congruent path reducing the perceived PFPS.
These categories of shoes offer higher resistance to fatigue of the lower leg muscles during running, particularly in runners with pronated feet. This finding again suggests that motion-control shoes might reduce overuse injuries in runners with pronated foot types.
The following section covers the impact of various shoe features (like shoe weight/shoe lacing pattern, shoe upper) on the muscle activity and the risk of running-related injuries.
Impact of shoe weight on muscle activation and running injury risk
Impact on muscle activation
Shoe weight leads to increased muscle activation. The lightest shoes might increase tibialis anterior muscle (outer side of shin) activity which prevents the slapping of foot on the ground at first contact and helps lift the foot at ankle.
The heaviest shoes could increase semitendinosus (hamstring) activity which propels the body forward during running. They could increase gastrocnemius lateralis and soleus muscle (calf muscles) activity during the stance and push-off phase.
Refer to my previous article for more details about the different phases of running and the muscle activity during each phase.
Impact on running injury risk
The peak vertical ground reaction force (GRF) increases with the weight of the running shoes. When running longer distances, the maximum vertical forces acting on the body are typically more than two times the body weight. Greater the GRF, greater running speeds are achieved. But along with increased speed, there are the increased injury risk. The higher magnitudes of impact forces and / or pronation that may occur during running are harmful to the human body and may lead to the development of running injuries.
Research indicates that the difference between a lightweight and heavyweight running shoe can easily exceed 200g, which would result in running economy changes of around 2% – significant for performance – especially over a longer running distances such as a half or full marathon. But this may also increase the risk of injuries due to higher impact forces.
Impact of shoe midsole on running injuries risk and running efficiency
Shoe midsole is the shock-absorbing layer of material within the shoe.
The design of the midsole enables the athlete to run better by optimal redistribution of positive lower limb joint work from the knee to the joint of your toes above the ball of your foot. The reduction in the rate and the magnitude of the impact forces to the musculoskeletal system leads to optimum force and energy transmission.
The softest running shoes midsoles can cause the runners to experience more impact force than the hardest midsoles. Thicker midsoles could provide better cushioning effects and attenuate shock during impacts but might also decrease plantar sensations of a foot at the touchdown.
Shoes with cushioned heels promote a heel-strike running pattern, whereas runners with neutral shoes and barefoot have a forefoot or mid-foot strike pattern. The high impact peak occurs with heel-strike and likely causes increased loads on the tibia, calcaneus, and plantar fascia thus increasing the injury risk.
The supinated foot has limited shock reduction capacity. So, the runners with a supinated foot type are recommended cushioned shoes which enhance force reduction upon ground contact.
Impact of shoe bending stiffness on running performance
Many studies conclude that increasing the stiffness of running shoes at the optimal range can benefit performance. Stiffer shoes would reduce energy expenditure while running, maximise VO2, energy loss at metatarsophalangeal joint ( joints in the bones of feet/ankle and toes) compared to a less tough one.
Impact of shoe lacing patterns
Much research has been conducted to study the impact of shoe lacing pattern on the risk of lower limb injuries and foot biomechanics while running. These research have typically examined the influence of the number of laced eyelets and lacing tightness (e.g., weak, regular and strong) on the biomechanics (including stability and comfort perception).
Following are a few derivations of these studies:
- The tightest (strong) and highest lacing (i.e., seven-eyelet) conditions reduced loading rates and rate of pronation of rearfoot motion.
- The lowest peak pressures at the heel and adjacent midfoot regions were observed in the high lacing pattern than in the lower lacing patterns.
- The low lace shoe conditions resulted in lower impacts and lower peak pressures under metatarsal heads (feet bones) which is probably induced by the foot sliding within the shoe.
- The firm foot-to-shoe coupling with higher lacing leads to a more effective use of running shoe features and is likely to reduce the risk of lower limb injury.
Impact of shoe upper
Shoe upper influence the fit and comfort of the shoe which changes the kinematic and kinetic strategies of runners. It was demonstrated in many research studies that firmer foot contact within a shoe would result in lower loading rates due to a better coupling of foot and the footwear. Even though this is argued, but still well researched that the structured upper shoes would provide greater movability and robustness, resulting in a uniformly distributed foot pressure and reduced loading at the bottom of the foot.
Scientist have provided excellent evidence on how running shoes absorb the running impact forces, improve dynamic stability, increase performance and running economy (metabolically efficient energy conservation) and increase the comfort levels of the runners. Each concluded research has led to better shoe design and improvement in comfort, cushioning and /or performance.
When we are in the process of understanding the importance of running shoes on the risk of injuries, it is very important to understand that there are numerous factors that leads to the running-related injuries. Increased impact forces, foot strike pattern and /or inefficient muscle activation are just a few of those. The importance of shoes in reducing that risk cannot be questioned. But while assessing the risk factors, it is imperative that we focus on other reasons too.