BODY SHOCK – an innovative running metric from fourth frontier x2
More: Fourth Frontier X2 Detailed Review
Body Shock refers to the speed at which force is applied to the foot during walking or running. Usually measured in force per unit of time, such as Newtons per second, peak loading rate is especially important in studies related to injury prevention. A higher loading rate can increase the risk of certain injuries.
For example, if your running routine involves switching between grass and roads, the impact on your joints varies significantly. On grass, the surface absorbs some of the physical impact, potentially reducing Body Shock. However, when you shift to hard surfaces, the Body Shock on your joints increases due to reduced shock absorption from the ground.
Fourth Frontier X2
24x7 ECG, Real-Time Alerts and Sports Tracking.
Tracking Body Shock is useful for individuals recovering from injury, as it can help guide the rehabilitation process and ensure the injured area is not subjected to excessive force too quickly. For athletes, understanding Body Shock can aid in fine-tuning running technique to optimise performance and efficiency while reducing strain on the musculoskeletal system. High Body Shock, especially during running, can be associated with a greater risk of injuries such as stress fractures, and by measuring and modifying this, it might be possible to reduce injury risk.
The Fourth Frontier X2 ECG also acts as a motion sensor device and records Body Shock with every foot strike, providing valuable data – similar to how Peak Loading Rate is measured in biomechanics and further similar to how Stryd use Leg Spring Stiffness. This information can be used to inform training and rehabilitation strategies, helping individuals to achieve their fitness and performance goals while minimizing the risk of injury.
frontier X2 also has an innovative heart rate metric analysing the ST segment of each heartbeat. When the amplitude of the ECG’s ST segment is compared to the amplitude of the PR segment (image below) and a difference of 0.2 millivolts or more is found, then we can infer electrolyte imbalances, conduction defects or oxygen deprivation – heart strain.
More: Fourth Frontier X2 Detailed Review
Fourth Frontier X2
24x7 ECG, Real-Time Alerts and Sports Tracking.
Last Updated on 28 January 2026 by the5krunner
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tfk is the founder and author of the5krunner, an independent endurance sports technology publication. With 20 years of hands-on testing of GPS watches and wearables, and competing in triathlons at an international age-group level, tfk provides in-depth expert analysis of fitness technology for serious athletes and endurance sport competitors.
