Isolated vs. functional training

Why is isolated training on DAVID exercise equipment an advantage over functional training? Patients with musculoskeletal complaints compensate for the complaints by using other muscle groups that take over the original movement. This physical compensation is a natural phenomenon but should be restored during rehabilitation.

The DAVID equipment uses isolation to activate muscle groups that the above phenomenon can restore. An example of this is the Hip-Fix on the DAVID Back Extension.¹

DAVID’s isolation principle

EMG validation studies were conducted in collaboration with the University of Cologne, Germany, to determine if DAVID’s isolation principle activated the target muscles (agonist) and blocked the surrounding solid muscles (antogonist). This example of the Back Extension Device results showed that the strong hip extensors were blocked and inhibited, creating a high activation level in the spinal target muscles.

Denner A. Muskuläre Profile der Wirbelsäule. Berlin, Heidelberg; Springer; 1997. Chapter 7.4, Ergebnisse Eigener Reliabilitäts- und Validitätsuntersuchungen; p. 163–178.

The Importance of Specific Training

There is a common belief that exercises with guided movement patterns using exercise devices are less effective than free-weight exercises that enhance overall coordination. However, this notion contains a fundamental error. Each exercise imparts specific skills relevant only to that particular movement and not much more. For instance, a bench press primarily trains the muscles and nervous system to perform that specific movement efficiently, with limited benefits.

We must question whether an exercise is the most effective and safe way to train the chest, shoulder, arms, and corresponding joints. In reality, a reverse correlation exists between the level of coordination required and the intensity of safe training. Exercises demanding higher coordination tend to have lower training intensity, while those with high intensity, like squats, carry a higher risk of injury. Squats can be highly effective at intense levels, but they also pose a significant risk to the back, leading to injuries, especially for young and enthusiastic individuals.

Therefore, it is vital to determine the primary motivation behind each exercise. Is it to become skillful in a specific movement, like bench press, or is it to strengthen the muscles and joints to function effectively in daily life or participate in sports safely? Understanding the purpose of each exercise helps us tailor training regimens that align with specific goals to prioritize overall strength, functionality, and safety.

Our philosophy is the latter and therefore our sole motivation is provide safe, effective and comfortable exercises for all relevant muscle groups and joints in the human body.

The Loading Principle in Exercise Equipment Design

When it comes to designing exercise machines, a significant distinction exists between multi-joint and single-joint exercises. In multi-joint exercises like the leg press, load regulation occurs automatically as the human skeletal leverage changes. In contrast, single-joint movements such as the leg extension require precise loading regulations, often accomplished with an eccentric cam. This critical difference means that even without restrictions in loading, a multi-joint training device can be quite effective as long as it functions smoothly and provides adequate seats, grips, and footplates.

However, the same cannot be said for single-joint movements. Many devices available in the market are far from being safe in this regard. While they may carry the CE mark indicating technical safety, little attention is given to biomechanical safety, which is equally crucial for ensuring effective and safe workouts.

At DAVID, we understand the importance of optimizing the loading principle in both multi-joint and single-joint exercises. Our exercise equipment is carefully designed to ensure biomechanical safety and effectiveness, providing users with a secure and productive training experience. By prioritizing both technical and biomechanical safety, we aim to deliver exercise machines that help users achieve their fitness goals while minimizing the risk of injury.

In a multi-joint movement the load is regulated by the changing “leverage arm” of the musculoskeletal system. In the beginning (red) the leverage is long, as legs are straightened (green) the leverage shortens and the load to muscles is reduced. In a single joint movement, the leverage arm remains the same in all positions and therefore the load must be regulated by the device.

Strength – length relationship of the Sarcomere

The first basis for the loading design is the functioning principle of the smallest part of the human muscle, the “Sarcomere”. Sarcomereconsists of two different elements, the ”myosin” and the “actin”. These elements slide within each other and are connected with “cross bridges”.

The number of active, interacting cross bridges determines the pulling strength of the sarcomere. The greatest number of interactions occurs at the midpoint of the length of the sacromere. When lengthened, many cross bridges are detached and when shortened, they cross over each other.

In short, purely concentric pulling force of the muscle is the greatest at the midpoint of the movement.

Stretch Shortening Cycle

This graph below shows the importance of eccentric / concentric cycle. Eccentric movement is when muscles are activated while lengthening and concentric movement when muscles are shortening. This diagram shows that muscles strength in the concentric phase is significantly higher when perceived by an eccentric phase (graph in the middle) compared to a situation where there is only concentric phase (graph on the left). This stored energy is lost if the eccentric phase is stopped for 0,9 seconds or more (graph on the right).

Electromyographic and force production characteristics of leg extensor muscles of elite weight lifters during isometric, concentric, and various stretch-shortening cycle exercises. (4)

This phenomenon is a critical characteristic of the muscles in real world situations where we have to face mass with inertia. Without even understanding this theory, we practice this in every-day situations. For example if we need to jump up, we go down first in a rapid movement before changing direction. This would seem unusual, since we have to first decelerate our body mass on the way down and again accelerate on the way up.

Artificial loading principles, like air pistons or electric motors can never imitate inertia in a proper way. This is a serious drawback, since inertia behaves totally differently during fast or slow movements and “stretch shortening cycle” is a critical component of muscle development. Combined with the David cam principle and natural loading with inertia, David can provide the most effective loading at any speed regardless of the training motivation.