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Injury Prevention In Swimming Series: Arm Entry

This article is about how the arm entry is a critical factor in freestyle swimming success and injury prevention of the shoulder.

In a study, the following technique conclusions were reached. Most females completed the arm entry with the hand above the shoulder. Most males completed the arm entry with the hand at the same level as the shoulder. An effective entry, is where the hand instantly begins generating propulsion and speed, basically having the arm under the shoulder during the entry phase.

Over 70% of the females completed the arm entry with a hand above the shoulder, and less than half of the males completed the arm entry with the hand above the shoulder, but for both males and females the exposure time to shoulder stress was significantly less with the swimmers that completed their arm entry with their hand level with the shoulder.

Next, something called “exposure time” was looked at. Exposure time was defined as the time exposed to shoulder stress as a time from the completion of arm entry until the hand is below the shoulder. It was shown that the exposure time is quite significant. For males the exposure time was over 1/10 of a second and for females it was over 1/4 of a second.


Next, something called the index of coordination was looked at, which plays a huge factor in freestyle swimming success. First, let’s look at the different levels of index of coordination (IOC).

  • 0 index of coordination is when the entry arm is in position to begin generating propulsion at the same time the opposite arm finishes generating propulsion.

  • A negative index of coordination is when the entry arm doesn’t begin to generate propulsion when the opposite arm finishes generating propulsion.

  • A positive index of coordination is when the entry arm begins generating propulsion before the opposite arm finishes generating propulsion.

The same study found that the entry phase decreased with an increase in swimming velocity/speed. It was also shown that the index of coordination increased with an increase in swimming speed. It has been shown that for swimmers to swim faster they need to decrease the entry phase and increase the index of coordination.


Next, it was hypothesized that swimmers that complete the arm entry with the hand level with the shoulder would have a lower exposure time, a higher index of coordination, and a faster swimming speed than swimmers that completed the arm entry with the hand above the shoulder. A study was done to test this hypothesis using 108 university swimmers (70 males and 38 females).

Swimming with an arm entry where the hand is level to or below the shoulder will decrease shoulder stress significantly as well as increase swimming speed.

The swimmers swam with pressure sensors that were strapped to the swimmer’s arms so that they could swim freely with no difficulty. The pressure sensors measured the pressure difference between the palm of the hand and the back of the hand, and force was calculated using the surface area of the hand.


Each swimmer sprinted one lap to the wall, and data was captured over the last 10 meters. It took the average female swimmer about 2/10 of the second to get her hand below the level of her shoulder.


There was a significant difference in the distribution of swimmers by gender and arm entry position. Over 70% of the females completed the arm entry with a hand above the shoulder, and less than half of the males completed the arm entry with the hand above the shoulder, but for both males and females the exposure time to shoulder stress was significantly less with the swimmers that completed their arm entry with their hand level with the shoulder.


Males and females who completed their arm entry with the hand level with the shoulder had an identical exposure time. For both males and females, the index of coordination was significantly higher for the swimmers who completed their arm entry with the hand level with the shoulder. Males and females who completed their arm entry with a hand level with a shoulder had an identical index of coordination. For both males and females swimming velocity was faster for the swimmers who completed their arm entry with the hand level with the shoulder. The significance of the effects were substantial particularly for the exposure time to shoulder stress and for the index of coordination.


In conclusion, swimming with an arm entry where the hand is level to or below the shoulder will decrease shoulder stress significantly as well as increase swimming speed.

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