The beach offers several unique features for enhanced training. For example, we can work against the water resistance, we can use the instability of the sand for balance training, we can use the softness of the sand to reduce impact loads on the body, and we can use the “heaviness” of the sand to increase metabolism.
The water creates hydrodynamic resistance. When you are moving your body or an object in the water, the effect of gravity on the load is diminished because of the buoyant forces acting upward in the water. Instead of gravity being the resistance, you are now working against the resistance of the water. The resistance of the water is always working opposite the direction of movement.
The forces you need to produce in order to overcome the water resistance depend on the following:
- The area of the body or object that is facing the movement direction.
- The velocity of your movement squared (v 2).
- The shape of the body or object that is moving through the water.
- The degree of friction between you and the water.
This means that the larger the area of your body or an object that is facing the movement direction, the more force you need to produce. It also means that it requires a substantial increase of force to increase the velocity of your movement just a little bit. This is because the forces required are proportional to the velocity squared.
Walking lunges in waist high water is an example of an exercise you can do (see Figure 1).
Walk as fast as you can for the desired number of steps (depends on your goal). Add a barbell or any kind of dragging device if added resistance is necessary.
The Sand is Unstable
As we attempt to maintain static balance standing on one leg, we often find ourselves making small adjustments on the stance foot in the form of eversion/inversion movements that shift the pressure between the external and internal edge of the foot.
These small movements are more taxing to perform on soft sand because it moves. When the internal edge of your foot “finds” the sand, it is expecting your steady living room floor. Instead, the sand moves, and the nervous system must “adjust the adjustment” in order not to fall.
The instability of the sand varies significantly with the type of sand you are standing in. If the sand is hard and wet, it might be easier to perform a balance exercise on the beach. The sand takes shape after your foot and you kind of “sink into it.” In general, balance exercises should be performed in soft sand.
However, there is an even harder way to practice balance on the beach. The hard way is to go to the edge of the beach, where the waves come in. When the waves move out again, there is a small strip of the beach where the top layer of sand is pulled out by the wave.
To some degree, the edge of the beach is more challenging than a balance board. On a balance board, the degree of instability is constant. You are constantly being challenged. On the edge of the beach, the degree of instability changes with the coming and the going of the waves. In the time span between two waves, you think you are fine. Then the wave comes in, you feel the instability, but you maintain balance. Then, there is a shock as the wave moves out again and pulls the sand along. If you are good, you maintained your balance.
You can benefit from this feature of the beach by performing single leg exercises like the “clock” (see Figures 2 and 3) at the edge of the beach.
Reach for imaginary points corresponding to approximately 9:00 and 3:00. Complete at least one semi-circle before repeating with the other leg.
The Sand is Soft
When we walk, run, sprint or jump on a steady surface, each foot contact creates an impact force.
To get an idea of how our bodies experience this impact force, take your bathroom scale and drop a two to three pound item on it. Watch how the indicator violently rises before settling at the level corresponding to the weight of the item.
Impact forces can be of substantial magnitude (see below table).
|Type of Activity||Impact Forces (g)|
|Walking||0.5 – 1.0 g (3)|
|Jumping (from 0.45 meters)||5-7 g (4)|
These forces travel up through the body, but we are designed in such a way that our fascia and muscles dissipate these forces before they reach the cranium. This process of dissipation depends, among other things, on the supporting surface.
Thus, because of the sand’s yielding properties, impact forces experienced when running, sprinting or jumping on the beach are reduced, compared to performing similar activities on a steady surface.
The body will experience significantly different levels of impact forces depending on the type of sand you’re moving on. There is a four times greater impact force on wet compacted sand compared to dry uncompacted sand.
Being able to reduce impact forces can be beneficial (necessary) during rehabilitation of lower extremity injuries. Also in training stages with increasing and/or large volumes of running, sprinting or jumping, it can be beneficial to perform a certain percentage of this volume in a low impact environment.
Now, if we run or jump on sand, the contact phase between the feet and the ground will, for some athletes, be longer. This happen because the sand moves as force is applied to it. The longer contact phase means we are practicing a slower movement pattern compared to performing the same activity on a harder surface.
This is no problem if your primary sport takes place on the beach, but since the basic principle of training specificity tells us that “train slow, be slow,” we need to understand how sand training affects our performance on harder surfaces, if that is our goal.
Performing plyometric and sprint training in sand can improve speed and jumping ability in soccer players. Furthermore, there seems to be a high correlation between jumping ability in sand and jumping ability on a hard surface. This means that to some degree, the same capacities are behind performance on both surfaces.
However, after a period of training in sand, at least three to four weeks should be spent optimizing recruitment patterns for harder surfaces, if performance in those types of environments is the goal.
The Sand is “Heavy”
The dry un-compacted sand is soft on our tendons and joints because it moves when we land on it. But for the same reason, it is also more demanding to run, sprint or jump in the sand.
Running on sand has a 1.2 to 1.6 times greater energy cost compared to running on a firm surface.
If you are walking (at speeds exceeding 3 km/h), the difference in energy cost increases to about 1.8 to 2.7 times more on sand than on a firm surface.
The same pattern is seen during repetitive jumping exercises. The energy consumption during jumping in sand is about 120 percent of the energy consumption during jumping on a firm surface. Also, your maximal jump high is significantly reduced.
The increased energy consumption when running, walking or jumping in sand can be explained by the following:
- A reduced recovery of potential, kinetic and elastic energy.
- A decrease in efficiency of the positive (in take off phase) work done by muscles and tendons.
These effects take place because the sand moves as force is applied to it. This slows down the total contact time, including the amortization phase of the stretch shortening cycle. This means that the increased impulse normally created by any stretch shortening cycle is diminished.
In other words, running or jumping on sand shifts the emphasis from eccentric work (including strain on tendons and joints) to concentric work performed by the contractile component of the muscle tendon complex.
This feature of the sand is relevant for weight loss (the increase in energy cost) or for energy systems work with a focus on anaerobic lactic metabolism. Regular protocols for walking, running or sprinting can be used.
It should be remembered that walking, running and jumping in sand increases various movements of the foot (flexion, eversion/inversion). The volume and intensity of training should increase gradually in order for the athlete/client to get accustomed to these movements.
Further features of training on the beach (and outdoor training in general) include training in fresh air, under the healing sun (at temperatures below 18 degrees C). Also, beach training offers the opportunity to train barefooted, which has several beneficial effects as well.
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