Treadmills remain one of the most popular types of cardio equipment. Regular use strengthens the cardiovascular system, improves aerobic endurance, enhances respiratory function, maintains muscle tone, and helps reduce body fat. For many people, it is also a way to relieve stress and boost mood through the release of endorphins and endocannabinoids during prolonged rhythmic exercise.
In this article, we will examine the two main types of treadmills: mechanical and electric. We will look at the key differences, their impact on movement biomechanics, and what to pay attention to when choosing.
Operating Principle
The main structural difference is the presence or absence of an electric motor.
An electric treadmill. The motor drives the running belt. Speed is set on the control panel and maintained automatically. The user adapts to the set pace.
A mechanical treadmill. There is no motor. The belt moves solely through the user's muscular effort: on every step, you must push the belt backward. To adjust resistance and smooth out the motion, these treadmills can be equipped with a magnetic brake.
There is also a separate category of curved mechanical treadmills, where the belt has a concave shape. The principle is the same: no motor, movement comes entirely from human effort, but the shape of the deck additionally affects gait biomechanics (more on this below).
Muscle Activation and Energy Expenditure
At comparable running speeds:
An electric treadmill reduces the need for horizontal push-off. The belt moves on its own, and the user mainly needs to keep up with moving their legs to stay on the belt. The push-off phase is less pronounced than in natural walking or running on a surface. Accordingly, activation of the posterior chain muscles (glutes, hamstrings, calves) during the stance phase is somewhat lower.
A mechanical treadmill requires full-force push-off on every step. This brings the pattern closer to the natural locomotor cycle, where the horizontal component of effort is necessary to move the body's center of mass forward. Studies show that metabolic cost on a mechanical treadmill at the same speed can be 20–30% higher compared to an electric one. This is a direct consequence of the fact that the person is the "motor."
Impact on Gait Pattern
An electric treadmill.
The moving belt carries the stance leg backward (hip extension), which can lead to a shortened push-off phase and reduced stride length. Several studies have documented decreased hip extension range and plantar flexion (ankle plantar flexion) when running on an electric treadmill compared to running on a solid surface. In simple terms, the foot "under-pushes" because the belt is already moving backward on its own.
A mechanical treadmill (flat).
The user determines both the pace and stride length. The need to push the belt stimulates active engagement of the foot, ankle joint, and calf muscles. This can help develop push-off strength and maintain ankle mobility.
A curved mechanical treadmill.
Requires even greater muscle activation. However, there is an important nuance: due to the concave shape of the deck, foot contact with the surface occurs earlier in the gait cycle and typically lands on the distal metatarsals and metatarsophalangeal joints (front of the foot). This can limit ankle dorsiflexion during the stance phase and create increased stress on the metatarsal bones, Achilles tendon, and plantar fascia during prolonged use, especially in untrained individuals.
Cushioning and Impact Loading
It is important not to confuse two things here.
Many electric treadmills are equipped with deck cushioning systems (springs, elastomers, special suspensions). It is the design of the deck and cushioning system that reduces impact loading on the joints, not the movement of the belt itself. The smooth belt motion provides comfort, but vertical impact forces are absorbed by the deck.
Mechanical treadmills generally have a stiffer deck with minimal cushioning. Impact loading on the lower extremity joints during running may be higher. This should be considered if you have joint problems, excess body weight, or an insufficient fitness level.
Who Each Type Is Best For
An electric treadmill is a good choice for:
Beginners who need a stable and predictable speed
People with excess body weight or joint problems (provided the treadmill has a good cushioning system)
Those who want to use built-in programs (interval, endurance, heart rate control, etc.)
Training with controlled incline (simulating uphill running)
A mechanical treadmill is suitable for:
Developing push-off strength and strengthening lower extremity muscles
Building a more natural gait pattern
Training self-paced control: acceleration and deceleration happen organically, without delays from program switching
Improving blood flow from the lower extremities in cases of venous insufficiency
Those who want to increase energy expenditure at the same speed
A curved treadmill is ideal for:
Athletic and well-trained individuals
Sprint and interval training
Developing explosive power and push-off force
However, due to the specific deck shape, it may not be suitable for long-distance running or low-intensity walking, nor for individuals with limited ankle mobility or foot pathologies.
General Selection Guidelines
When choosing a treadmill type, consider:
Your fitness level
Individual anthropometric data (height, leg length → belt length and width)
Condition of lower extremity joints and ankle mobility
History of injuries or their absence
Ability to control your own body in motion (coordination, proprioception)
Specific training goals
Alternative: Walking and Running Outdoors
If the main goal is to accumulate a large volume of walking, then in suitable weather the best option remains regular outdoor walking. This is the most natural form of locomotion: varied terrain, different surfaces, wind, the need to navigate around obstacles — all of this engages stabilizer muscles, trains coordination, and creates the very pattern of chaotic intensity changes characteristic of fartlek (variable-speed training).
No treadmill, no matter how advanced, can fully replace natural outdoor movement. But as a tool for controlled indoor training, it is an excellent option.