How Exoskeletons Prevent Hiking Knee Injuries

I. Why Are Knees Prone to Injury?

1.  In daily activities, the knee joint bears internal loads far exceeding body weight. Classic biomechanical studies using kinematics and musculoskeletal modeling on healthy adults estimate that during normal stair climbing, the distal-proximal (primary compression direction) contact force at the tibiofemoral joint averages about 3 times body weight, with peaks reaching approximately 6 times body weight at higher flexion angles.

Source: Knee and hip kinetics during normal stair climbing - PubMed

2.  This indicates that even in seemingly ordinary actions like “climbing stairs,” internal knee forces are multiples of body weight. In scenarios like hiking, which involve prolonged, frequent repetition and varied terrain, tissues like cartilage, meniscus, and ligaments are more susceptible to cumulative damage. This is precisely why exoskeleton robots are needed to assist in protecting the knee joint.A counterintuitive fact: the core source of stress within the knee joint is muscle activity, not just body weight! The primary muscle groups involved are the hamstrings and quadriceps, which act as antagonistic pairs. During normal walking, these muscle groups remain in a prolonged state of antagonistic co-activation, causing the actual internal knee pressure to be much greater than the pressure exerted by body weight alone. Related research shows that during walking, regardless of load carriage, muscles contribute over 65% to the knee joint contact forces.

Source: Tibiofemoral joint contact forces increase with load magnitude and walking speed but remain almost unchanged with different types of carried load - PMC

Specifically, approximately 20% of the contact loading was attributed to the quadriceps muscles. Thus, while the magnitude of tibiofemoral contact forces increases with carried load and walking speed, the relative contributions of muscle and external load to these forces do not change.

II. How Do Hip-Assist Exoskeleton Robots Protect the Knee Joint?

1.  From the previous section, we established that the primary source of internal knee stress is muscular. Therefore, reducing the force output of either the hamstrings or quadriceps can directly decrease the overall internal knee pressure. This is precisely why individuals with knee pain instinctively use their hands to support their knees when climbing stairs a typical antalgic (pain-avoiding) gait adaptation.

Source: Antalgic Gait in Adults - StatPearls - NCBI Bookshelf

Furthermore, research shows that compared to a “normal squat,” a “hand-supported squat” significantly reduces peak tibiofemoral joint force, suggesting that hand support can lower knee joint loading.

Source: Effect of hand support during squats on tibiofemoral and patellofemoral joint forces - PubMed

2.  The brain’s motor control neurons play a crucial role in this process. A well-established conclusion is that human movement exhibits strong adaptive characteristics. During motion, the body automatically and dynamically adjusts muscle activation. When an external force intervenes in the movement process, muscles adaptively reduce their output to maintain a movement trajectory as close as possible to the expected trajectory without intervention.

Source: Learning to walk with a robotic ankle exoskeleton - ScienceDirect

3.  Consequently, when a hip-assist exoskeleton robot, through external force application, alters the force demand on the quadriceps and hamstrings, this antagonistic pair will adaptively reduce their overall co-activation output, thereby lowering internal knee stress and achieving a protective effect.Theory established, let’s examine if experimental data supports this. A study on a hip-assist exoskeleton robot a device that seemingly does not directly assist knee flexion/extension demonstrates its effectiveness. The points where the device applies hip extension and flexion forces are located on the lower thigh, just above the knee. This mimics the classic support position of “hand-on-knee” assistance. Thus, it can alter the coordination of muscles involved in knee extension and flexion. The study recorded electromyography (EMG) data from key muscles. Activity in the rectus femoris (a quadriceps muscle) decreased by an average of 33.56%.

Source: Frontiers | Reducing the muscle activity of walking using a portable hip exoskeleton based on human-in-the-loop optimization

(Note: EMG is a reliable indicator of actual muscle force output.)

The benefits of hip-assist exoskeletons can even extend to the ankle joint. The following paper demonstrates that although assistance is applied only at the hip, the user’s hip and ankle muscle activations significantly decrease. This indicates that hip assistance can alter muscle coordination along the kinetic chain and reduce antagonistic output in distal joints.

Source: Powered hip exoskeletons can reduce the user’s hip and ankle muscle activations during walking - PubMed

4.  In summary, hip-assist exoskeleton robots significantly reduce the force output of the two most important muscle groups for the knee—the quadriceps and hamstrings—during walking or climbing. This allows them to mimic the knee stress reduction of “hand-on-knee” support, forming a protective effect on the knee joint and thereby reducing the risk of injury under the same activity intensity. Additionally, research shows that hip-assist exoskeleton robots provide significant help in the recovery of patients after total knee arthroplasty, further supporting their protective role for the knee.

Source: Early Recovery of Walking Ability in Patients After Total Knee Arthroplasty Using a Hip-Wearable Exoskeleton Robot: A Case-Controlled Clinical Trial - PMC

III. How to Choose an Exoskeleton Robot?

Since exoskeleton robots can indeed protect the knees during hiking, the next question is how to choose an effective product.

1.  First, it’s important to note that the control algorithm (assistance timing/human-robot coupling method) of an exoskeleton largely determines its impact on knee joint load. When the algorithm matches human movement, it can reduce muscle force and protect joints. When the algorithm is inappropriate, it may not only fail to save effort but could even potentially cause joint stress. As shown in one study: peak knee compressive force during unassisted walking was about 3.10–3.48 times body weight. Under four different human-robot interaction modeling strategies, the peak knee compressive force during exoskeleton-assisted walking ranged from approximately 2.82 to 5.83 times body weight.

Source: Hip, knee, and ankle joint forces during exoskeletal-assisted walking: Comparison of approaches to simulate human-robot interactions | PLOS One

2.  Now, let’s compare some popular exoskeleton products through key parameters: Dnsys X1, Hypershell X, and VIGX π6.

Comparison of Exoskeleton Product Parameters

• Weight: VIGX π6 has the lowest total weight at 1.9kg. This directly reduces the absolute burden of wearing the device. Furthermore, with a design that better aligns with the body’s center of mass, the VIGX π6 offers greater comfort during prolonged wear. (Note: Dnsys X1 and Hypershell X official websites do not list total weight, only mechanical part weight. The weights here are based on measurements.)
• Algorithm & Sensors: The most crucial aspect is the algorithm. Subjectively, all three products can provide a noticeable assistance effect. However, objective comparison is key. Besides motor state data, all three are equipped with 6-axis IMU sensors, enhancing the device’s perception of current movement state. Compared to the other two, the VIGX π6 adds a visible-light camera and a dTOF sensor. This allows for more direct perception and analysis of the user’s leg movements and terrain changes, greatly improving the accuracy of assistance mode switching and gait adaptation while reducing latency.
• Structural Design: Dnsys X1 and Hypershell X use the common dual-motor side-mounted power structure. VIGX π6 employs a single-motor front-mounted design. In comparison, the latter aligns the force line with the plane of thigh movement, making the assistance fit the natural gait better. This significantly reduces parasitic horizontal torque, markedly decreasing torso sway at high assistance levels, thereby improving wearing comfort and reducing wasted energy expenditure.

Overall, significant differences exist between products. Consumers should make comprehensive comparisons and choose a product with superior performance that better suits their needs. Especially when the primary goal is knee protection, greater attention should be paid to selecting the right device.