Coaches use many metrics to analyze swimming performance, both for competitive swimming and for training to become a faster swimmer. Most common among the metrics—besides time—are swim velocity, stroke count, stroke rate, and stroke length.
There have been numerous studies measuring force development of the swimmer’s body using tethered swims, where the swimmer is strapped onto a wire or line that is connected to a strain gauge on land that measures the force the swimmer produces while swimming. Santos et al.1 showed that asymmetries between propulsive forces generated by each side of the body can be detected using tethered swim measurements, but being able to measure the propulsive force and its proportion of total force development in each individual stroke is relatively new—and provides another way to measure and analyze a swimmer’s performance, as well as monitor training progression.
Force data provides another objective way to look at swimming technique, specifically efficiency—if a swimmer can learn to swim faster, but still use less force in each stroke, then their efficiency of moving through the water has improved.
Moreover, measuring force for tethered swims is not necessarily convenient or easy to do during everyday practice, but a smart new sport technology that every coach can use is capable of adding further insight into swimmers’ potential for improvement. Force measurements are another piece of the swimming technique puzzle, and it is a new and exciting piece to dive into: being able to optimize training both in the water and on land.Force measurements are another piece of the swimming technique puzzle, and it is a new & exciting piece to dive into: being able to optimize training in the water & on land. Click To Tweet
Does Strength on Land Automatically Convert to More Force in the Water and to Faster Swimming?
As a collegiate swimmer at the University of Cincinnati, I often wondered why some of my teammates could outperform me during dryland and strength training, yet I would swim faster than them. Since we were all Division 1 swimmers swimming at a high level, one could argue that all of us should have good technique and swim with similar, relatively low, resistance. What, then, was the differentiating factor?
Many years later, as a coach, I have seen several swimmers who are strong on land but not able to use that strength properly in the water. My background in research and analytics—coupled with my curiosity—led me to want to find out if force development on land corresponds to force development in the water. Being able to measure force development on land, and in the water for each arm stroke, offers the possibility of finding asymmetries between the right and left arm, and provides the ability to tailor and monitor a training plan to improve both force development and symmetry of the stroke technique.
Force Development in the Water—Does It Matter?
Force exerted by a moving object equals its mass times its acceleration; in swimming, however, this equation becomes a little bit more complex. Water density, resistance, and drag are among the factors that need to be considered when calculating force in the water. However, if these factors remain constant between swims, then increasing force should result in an increase in swim velocity.
High-level swimmers all have low resistance in the water, meaning that focusing on improving force generation (while maintaining the same low resistance) will improve swimming velocity. For more inexperienced swimmers, lowering resistance—by improving body position in the water through improved technique—will allow them to increase swim velocity while maintaining the same level of force generation. Being able to measure force in swimming is beneficial to both highly skilled swimmers and less-experienced swimmers and is a great objective way to look at swimming technique.The ability to measure force in swimming is beneficial to both highly skilled swimmers and less-experienced swimmers and is a great objective way to look at swimming technique. Click To Tweet
Can We Compare Force Development in the Water and on Land in a Swimming-Specific Manner?
I set out to find the answer to this question, together with coach Jack Fabian (Ph.D.) at Keene State College in New Hampshire, as combined we have several years of experience working with sport tech and equipment that helps improve swim performance.
I have been working with stroke technique analysis for several years, and in the past two years with a novel piece of sport tech called SmartPaddle, created by the Finnish company Trainesense. The SmartPaddle measures force development in the water during regular free swimming (untethered) and provides insight into the stroke technique for each arm individually. Connecting the data with video analysis provides a powerful combination to get a larger picture of the swimmer’s stroke and where and why it falls apart at fatigue. Being able to address any asymmetries between right arm stroke and left arm stroke is especially powerful, as this is data that has not been this readily available to coaches until now.
Force data is measured in three directions by the SmartPaddle: lateral sideways force, vertical force, and lateral propulsive force. The propulsive force is the force that generates the swimming speed forward, and hence the force that we want to see optimized and maximized for increased swim velocity. Force data is presented in graphs that provide a valuable overview of how the overall force is being used in each stroke—what proportion of the force generated is used for propulsive movement and how it changes from entry to pull phase to push phase to exit—and therefore where the stroke mechanics can be improved to make swimming more efficient. SmartPaddle also provides metrics like stroke count, stroke rate, impulse, splits, and hand velocity, which provide a comprehensive picture of the stroke together with traditional video analysis.
Coach Jack Fabian is an expert on using the VASA SwimErgometer and is therefore a great match in this endeavor to look at force development on land and in the water. The VASA SwimErg provides dryland training that is very specific for swimming in that it mimics swimming’s push and pull phase. It can be used to train proper swim mechanics at the fatigued state and to improve force development in the swim once the swimmer becomes fatigued.
Real-time data was provided with the ANT+ Wireless Power Meter, which, in this study, was connected to a training program (in this case, TrainerRoad) to record and monitor data during sessions, and to store, compare, and analyze over time. Metrics include power (in watts), distance, splits, stroke count, and stroke rate; for our purposes, we monitored and recorded stroke rate, time, and power.
This study was a first look at force and power in the water and on land, and we wanted to make the measurements as similar as possible between land (VASA SwimErg) and water (SmartPaddle). Protocols for land and water both consisted of a step test in six steps where stroke rate was increased, according to 40 – 43 – 46 – 49 – 52 – 55 strokes per minute (SPM) respectively.This study was a first look at force & power in the water & on land, and we wanted to make the measurements as similar as possible between land (VASA SwimErg) and water (SmartPaddle. Click To Tweet
On the VASA SwimErg, swimmers were to maintain the stroke rates for 90 seconds for each effort, and in the water the swims were 150 yards for each effort, which roughly corresponded to 90 seconds of swimming for the swimmers tested. Furthermore, they swam with a pull buoy and ankle strap to take out the effect of kicking as best possible, for better comparison to the measurements on land which isolate the upper body movements. Stroke rate was set and monitored by using FINIS Tempo Trainers in the water, and by the TrainerRoad program for the efforts on the SwimErgometer.
A SmartPaddle measures force (Newtons) and the VASA SwimErg power (watts), but since power equals propulsive force times velocity, there is a correlation between propulsive force and power. In this study, we looked at the relative change in force and how it correlates to the relative change in power once the swimmers fatigue. This indicates where the swimmer has potential to improve.
Findings of This Initial Look at Force Development in the Water vs. on Land
Question #1: Is there a correlation between being able to generate a lot of force or power on land and the ability to produce force or power in the water?
Yes, for the swimmers tested there was a linear relationship between the relative change in force in the water and the relative change in power on land that indicates a correlation between being able to develop power (or force) on land and being able to generate force in the water.
Question #2: Does higher force development correlate to faster swimming velocity?
Yes—for these swimmers, the ability to generate a lot of power on land meant being able to generate faster swim velocity. However, the swimmer with the highest force development on land was not the fastest in the water once fatigue set in. The swimmer who reached the highest swim velocity was the one who needed the least amount of force to increase swim velocity—i.e., the swimmer with the more efficient swim technique.
Question #3: Is a decrease in velocity due to a decrease in force development or to an increase in resistance (surface area)? If it is due to an increase in resistance, then the same drop in force/power should not be seen on land.
Force development decreased as the stroke rate increased and the swimmer fatigued, seen both in the VASA SwimErg measurements and with the SmartPaddle measurements. This indicates that the decrease in force in the water is not only due to an increase in resistance; there is a fatigue component that can be trained and improved on land, that can be carried over into swimming.The SmartPaddle provides great insight to any asymmetries in the stroke mechanics that might not be visible to the coach, in terms of force generation and efficiency. Click To Tweet
Furthermore, the asymmetries in force development between right arm and left arm when swimming were seen in the measurements on land on the VASA SwimErg, which means there is potential in improving the efficiency within the overall stroke mechanics by making the sides more symmetrical and similar in force development. This asymmetry can easily be addressed, improved, and monitored on the VASA SwimErg, as the data is in real time, and a coach can adjust technique instantaneously during the training.
This study found a linear relationship between propulsive force and velocity, and, once the swimmer fatigues, there was a significant drop in force and velocity when swimming at maximum speed. The strength of each stroke can be measured as impulse per stroke, as impulse equals propulsive force times the time interval of the propulsive part of the stroke. As stroke rate increases, the stroke length decreases, which means a shorter time interval for the propulsive part of the stroke. This in turn leads to less time to generate force, and hence impulse (strength) per stroke decreases. Focusing on maintaining stroke length and force generation per stroke when fatigue sets in will improve the impulse per stroke, and hence improve the ability to maintain a higher swim velocity for a longer time during a race performance.
Question #4: Will improving power on land automatically mean an improvement in the water?
Improving strength on land that is relevant to the movements of swimming can lead to improved force development in the water, both in terms of overall strength and in a more symmetrical stroke technique and force development, but of course the swimmer needs to use the proper mechanics both on land and in the water to see this gain. Although proper stroke mechanics can differ depending on the coach you ask, from a subjective standpoint there are objective measures that indicate whether the stroke mechanics are more efficient or not.
Measuring force as a means of improving stroke technique is valuable in terms of being able to assess if the large swimmers’ muscles (e.g., latissimus dorsi) are being activated, as proper activation means higher force generation. Once proper muscle activation is achieved, the next step is to maximize the amount of propulsive force: the SmartPaddle’s measurements provide insights into the efficiency of the stroke by showing what proportion of the total force developed is propulsive force. Pinpointing where the pull can be improved is easily done with force curves, and specific parts of the pull can become more efficient in terms of the proportion of propulsive force.
Application of Force Measurements on Land and in the Water—Why It Matters
Dryland programs can be designed with more specificity to swimming movements, and that targets a specific need of the athlete. Besides the obvious gains in strength of the swim stroke, a training plan where dryland training and swim training work in conjunction to maximize the potential of the athlete can reduce the occurrence of injuries due to overuse during hours of swimming, as stroke technique can be improved on land. Being able to target the specific areas of improvement on land allows for less time in the pool and more focus on building speed and endurance with efficient force development while swimming.Being able to target the specific areas of improvement on land allows for less time in the pool and more focus on building speed and endurance with efficient force development while swimming. Click To Tweet
The SmartPaddle allows for a way to monitor that the dryland program provides the desired effect. In addition, the SmartPaddle also provides great insight to any asymmetries in the stroke mechanics that might not be visible to the coach, in terms of force generation and efficiency.
Of course, there are other aspects of efficient swimming technique, but force measurements are one important piece of the puzzle that is now available to coaches and athletes. Force measurements in conjunction with video analysis and standard metrics like stroke rate and swim velocity provide a very powerful insight into how to become a more efficient and faster swimmer.
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1. K.B. dos Santos, G. Pereira, M. Papoti, P.C.B. Bento, and A. Rodacki. “Propulsive Force Asymmetry during Tethered-Swimming.” International Journal of Sports Medicine. 2013; 34: 606-611.