When a person is running his body is moving continously up and down a weight carried in a bag affects the motion of the bag and thereby the body.

• a) The body has completed its downward and start its upward movement from the lowest position;$$\begin{gathered} {\text{F}}_{\text{dn}}{\text{= F}}_{\text{t}}{\text{+ F}}_{\text{i}}{\text{- F}}_{\text{f}}\text{=} \\ {\text{= m (g+A}}_{\text{up}}{\text{) + m W}}^{\text{2}}{}_{\text{dn}}\text{/}{\text{}}_{{\text{2}}_{\text{s}}}{\text{- F}}_{\text{f}} \end{gathered}$$
• b) The body starts to fall from the highest position;$$\begin{gathered} {\text{F}}_{\text{up}}{\text{= -F}}_{\text{t}}{\text{+ F}}_{\text{i}}{\text{- F}}_{\text{f}}\text{=} \\ {\text{= - m (g-A}}_{\text{dn}}{\text{) + m W}}^{\text{2}}{}_{\text{up}}\text{/}{\text{}}_{{\text{2}}_{\text{s}}}{\text{- F}}_{\text{f}} \end{gathered}$$ Where:
  • F_t = gravitational force
  • F_i = inertial force
  • F_f = frictional forces
  • A_up = acceleration of the body in upward movement
  • A_dn = acceleration of the body in downward movement
  • W_up = velocity of the weight in upward movement
  • W_dn = velocity of the weight in downward movement
  • m = mass of the weight
  • s = displacement, distance, there inertial forces act to stop the downward or upward movement of the weight and to direct it downward or upward again.

The document USA 4,878,606 presents a device comprising a waist belt, a shoulder strap, an adjustable underarm strap. A bag is supported by waist belt by means of a multiple belt loop system adjacent the user's hip.

The human body is continuosly moving. A bag has to follow the complecated movement of the body. The presented device does not provide appropriate directed elasticity to hold a bag and its contents securely in place with a minimum impact to the body during the complicated movements. In the case the bag is fixed too tight or too loose to the body of user it creates discomfort and even injury by long time use with heavier loads.

The presented device has a diagonnally crossing shoulder strap and underarm strap to hold the shoulder strap in its proper place, which is a result of lacking elasticity. The tight waist belt does not allow to distribute weight automatically and accordingly to movements.The shoulder strap is attached to the ends of the bag.

In ordinary devices the weight of a load is not fixed in its position inside of bag and will move with a greater velocity than the bag. Thus F_i consists of two components, i.e. the mass and velocity of the weight contributing the inertial force When these forces become sufficiently strong the weight and the bag begin to move relative to the body. When displacement s becomes sufficiently great the weight creates a discord relative to the motion of the body.

In this way the weight and the bag fall out of the step with the motion of the body which the carrier experiences as an unpleasent bouncing movement. Displacement s becomes even greater.

If it is necessary to carry paper or documents in format up to A4, to move around freely and to have hands free while having a breast pocket available at the same time, there are at present no known device which permit to insert or take out materials without taking off first a bag. The invention as claimed provides a solution to this problem.

The purpose of the invention is to keep the displacement s at a so low level that it does not disturb a carrier The invention is directed to a device which comprises an elastic waist belt (D), a shoulder strap (A) and a bag or holder (E). The shoulder strap (A) is attached to the elastic waist belt (D) by an adjustable fastening (B), which is adjustable along the elastic waist belt (D). The upper end of the bag or the holder (E) is attached to the shoulder strap (A) and the lower part of the bag is formed adjustable on the elastic waist belt (D) by means of an adjustable fastening (F), which slides along the elastic waist belt (D). The bag or holder may be detached from the shoulder strap (A). The elastic waist belt (D) has different elasticities on the front and rear side and least one buckle (C,G).

Equations (1) and (2) show that the lower the level of displacement s the greater forces are acting upon the device and thereby the body of a carrier. With the device of the invention the weight is pressed tightly against the body and thereby reducing the moment of the weight upon the carrier's shoulder and subsequently increasing the friction. This together with the elasticity of the of the belts, holds bag and its contents stationary. The counteractive force of the elasticity is proportional to displacement s.

The forces F_up and F_dn act on a relatively limited area of the body.When a person runs or jumps the body begins to fall with an acceleration g,whereby $\text{a=g}$.Thus F_t =0 and weight strikes the bag and thereby the body upward with the inertial force F_i. Equations (1) and (2) show that F_dn is always greater than F_up.

Accordingly a harder fastening is needed when the body moves upward; than the body starts to fall. Usually a weight is bound equally in the both cases or a bag is hanging on the belt (D).

The elastic waist belt (D) which enables a dampening effect downward together with the friction of the shoulder strap (A) counteract the force F_dn on the both sides of the body. When the body starts to fall the elastic waist belt (D) acts only under the bag. In this way the same effect is achieved with less pressure and a lighter fastening to the body.

When the weight of the load is increased or the carrier begins to run instead of to walk, the equlibrium between forces F_dn F_up and forces fixing the bag become disrupted. With the bags ordinarily in use it would be necessary to take a bag off and open buckles to adjust the length of the belt or strap in order to fasten the bag more securely to the body or the weight and bag will be hold with hands which are not free in this case.

The invention has adjustable fastenings (B) and (F) which are adjustable along the elastic waist belt (D). It is not necessary to open any buckle or take off the bag to adjust the belt or strap. This is carried out simply by drawing the elastic waist belt (D) through the freely sliding fastening (F) and press the elastic waist belt (D) downward simultaneously (Fig.3.). The length of the elastic waist belt (D) and shoulder strap (A) is made adjustable for more ajdustment.

If a carrier suddenly falls or jumps a device will be exposed to considerably stronger forces. In this case the durability of the construction is put to a serious test. The invention effectively reduces an impact of heavier blows due to the elasticity of the elastic waist belt or belts (D). The bag or holder (E) is attached to upper end of the front side, which enables to fix the weight inside of the bag partly or entirely (Fig..2.) In a second embodiment of the invention two bags are connected to the elastic belt (D) comprising of two elastic waist belts sliding freely against one another (Fig.4.) and in a third embodiment the bags are jointed into one.

(Fig.5.) enabling the distribution the increasing pressure of the bag upon the waist belt and the shoulder strap and thereby on the body.