Swimming performance: may the force be with you

Andrew Sheaff examines the relationship between force production in the water and swimming performance, and provides training recommendations for aquatic strength training to enhance performance. 

Over time, strength training has become commonplace in more and more team sports, in addition to several individual sports. But only within the last 20 years has strength training been embraced by the endurance community, particularly by runners and cyclists. However, while much of the research supporting strength training in endurance sport has been performed on runners and cyclists, the research support for traditional strength training for swimmers is much weaker. This is most likely due to the nature of force application in the pool. Applying pressure to water is a lot different than putting pressure into the ground or a bike crank!

In spite of a lack of scientific support, strength training is certainly practiced by swimmers. However, it seems that most programs are implemented from a ‘because we should’ perspective rather than with an understanding of how strength training can positively impact performance in the pool. In this article, we’ll explore how force production impacts performance in the water, as well as several effective strategies that you can incorporate in your training to improve force production.

Force production and performance

How important is force production to swimming performance? To determine the impact of strength and force production in swimming, swimmers are often tested by swimming in a stationary position against a tether, which is connected to a force gauge. Each swimmer’s individual force measurements are then compared to each swimmer’s speed over various distances. The evaluation of force profiles during tethered swimming has demonstrated to be very reliable(1). So, what does the research to date have to say?

The impulse, or force per unit time, during tethered swimming has been significantly related to swimming performance over 50-metres (m)(2). Further, another study found a direct relationship between force in the water and the velocity over 22.9m(3). Significant correlations were also found between average force during tethered swimming and 25m race velocity(4). When looking at distances longer than 50m, one study found relationships between force production and speed over 100m(5), and these findings were supported in similar studies(6-7). Force production in the water is therefore critical for sprinting success!

While it seems intuitive that the ‘sprint’ events would rely heavily on force production, what about 200m races, typically considered to be ‘middle distance’ events? Relationships between force production and race performance out to 200m have been demonstrated in multiple studies(8-11). In addition, high correlations have demonstrated in all four competitive strokes over 50-200m, so force is not just for the crawl swimmers(9)! As you can see, force production is not just important for the sprint events lasting 20-30s. It matters just as much in events lasting well over 2 minutes. Force production has even been found to be related to 500-yard crawl performance(12), implying that production matters for just about all swimmers.

Powering up

The evidence is pretty incontrovertible that force production in the water is related to performance over 50-200m – distances that represent the vast majority of swimming contributions. However, it’s often said that correlation does not equal causation. To build the case for resisted sprinting, we have to consider how resisted swimming affects force production acutely, and whether long-term training can enhance performance.

When considering the acute effect of resisted sprinting in the pool, researchers found that the impulse (force/time) and the peak pushing force were both higher while swimming with a parachute (see figure 1)(13). This implies that swimmers can overload force production by swimming with resistance. The question then becomes, is performance impacted when ‘aquatic strength training’ is employed for extended periods of time?

Figure 1: Swimming parachute

The Finis swim parachute. By increasing hydrostatic drag, a parachute allows swimmers to generate greater force production in the water for a given swimming speed.

This question was explored by a group of Greek scientists(14). They investigated the impact of a resisted sprint program on maximal velocity and competitive performance in swimmers. The specifics of the training high velocity training regimen can be found in table 1. Both the experimental group and the control group completed the high velocity training set described for a 12-week period, the only difference being the added resistance used in the experimental group. Both groups performed their standard swimming training for the remainder of each training week for the duration of the study.

Table 1: Training intervention #1
Set 1

3 rounds of:

2 x 50m 70% intensity

4 x 25m maximal intensity

Swimmers began a new repetition every 1 minute and 45 seconds


·        The training set was repeated 3 times per week for 12 weeks.

·        The experimental group performed the training with a resistive bucket.

·        The control group performed the same set without a resistive bucket.

The main results of the study can be found in figure 2. In a nutshell, the experimental group demonstrated significantly greater performance improvements than the control group, and these performance improvements were evident across 50m, 100m, and 200m events. As the only difference between the two training regimens was the inclusion of resisted sprinting, we can conclude the resisted sprinting will positively impact the majority of race distances targeted by swimmers in the pool. Beyond the impact on competitive performance, 10m sprint times were enhanced in the resisted group only, implying that improved performance was the result of enhanced maximal velocity.

Figure 2: Performance gains after resisted swimming using a towed bucket(14)

A more recent study followed up on these results with a similar training design(15). As with the Greek study, two groups of swimmers performed sprint sets four times per week. However, the experimental group performing resisted sprinting, while the control group performing regular sprinting. The specifics of training intervention can be found in table 2. When the results were tabulated, the American researchers found the 50m, 100m, and 200m swimming performances were enhanced in the experimental group only.

Table 2: Training Intervention #2
Training Set 1

3 rounds through

6 x 15m maximum effort

60s rest between repetitions

5 minutes between sets

Training Set 2

2 rounds through

4 x 25m maximum effort

90s rest between repetitions

5 minutes between sets


·        Each training set was repeated two times per week on separate days for 11 weeks

·        The experimental group performed the training with a resistive parachute.

·        The control group performed the same set without a resistive parachute.

When considering these two studies, as well as the theoretical rationale for resistance training in the pool, we have a compelling argument for resisted sprint training in the water. With this argument in hand, let’s take a look at how we can begin to implement resisted sprinting into a comprehensive training plan.

Technical matters

Many swimmers and coaches are concerned that resisted training in the water might harm swimming technique. A brief response would be to consider the studies described above. Even if the resistance training impaired technique, the swimmers got faster, so any technique impairment was outweighed by improvements in other qualities!

However, it appears that this fear is unfounded. In the study by the American scientists(15), there were no changes in 24 basic kinematic (movement) characteristics of the crawl stroke. Indeed, other research suggests that resisted training may actually improve technique, as opposed to impair it. Swimming with a parachute may enhance the continuity of propulsive action(13,16). This means that swimmers learn to reduce the time where no propulsion is created by either arm. This technical characteristic is critical for achieving high velocities for obvious reasons, particularly in sprinting(17).

It should be noted that there is some evidence that there may be a small change in the entry and catch phases of the stroke(18), although this effect is more common in fully tethered versus semi-tethered swimming (see figure 4). At the same time, the main propulsive phases are unaffected by tethered swimming. As these are the phases we are ultimately working to impact, there seems to be little concern that technique will be negatively impacted if appropriate resistances are chosen. More on that below!

Tethered vs. semi-tethered swimming
A quick note on terminology. In most testing situations, force production is measured through tethered swimming whereas most training interventions use semi-tethered swimming. What’s the difference? In tethered swimming, the swimmer is resisted and stationary in the water. No forward progress is made in the water. In semi-tethered swimming, the swimmer is resisted, but still moves forward in the water, albeit slowly! In the two training interventions we discussed, semi-tethered training was performed.

Getting wet

Hopefully, you’re convinced that force production is related to swimming performance, and resisted training in the pool can positively impact your performance.  Now it’s time to look at how to practically implement aquatic strength training into your training program. When doing so, you’ll have to consider how to resist your swimming, as well as the type of training intervention to use.

The first step is to determine how you plan to resist your swimming. The main idea is to increase the amount of drag you experience while moving through the water. Some commonly used equipment is listed, as well visual images in table 3. All of this equipment is inexpensive and available for commercial purchase. If you don’t have the means or opportunity to purchase any of the available equipment, use the images below as inspiration to ‘build’ your own gear. The major idea is to increase the resistance you experience as you swim. With this idea in mind, anything that fits the bill is appropriate.  Even a baggy t-shirt with pockets can be effective!

Table 3: Common aquatic resistance training gear
Commercial Resistance Gear


DragSox (see figure 3a)

Weight Belt

Elastic Tubing

Drag Suit

Do-It-Yourself Gear

Board Shorts


Plastic Bucket (see figure 3b)


Pulling Band



Kick Board

Figures 3a and 3b: Dragsox (top) and homemade drag bucket (bottom)

Using paddles and fins can serve to enhance the surface area of the hands and feet, respectively, which can further increase the overload on the muscles of the upper and lower body. Don’t worry about the type of fins or paddles – any type that feels comfortable to you should be good. In addition, using a pulling band or kick board can work to isolate the muscles responsible for kicking and pulling.

When choosing resistance equipment, it’s important to appreciate that more is not always better.  Excessive load can cause technical problems(19). While it’s important to create an overload, the overload should still allow you to retain the rhythm of your stroke. While swimming with resistance, your technique should feel very similar, just slowed slightly by the resistance. If it’s a colossal struggle, it’s too much!

Now that we’re set up with the appropriate training gear, it’s time to determine the best way to implement resisted training into the training program. As a starting point, consider the training sets used in the studies described above. When comparing the two training sets, you can set there is ample rest, short distances, and very high-quality efforts. If you choose to design your own training sets, keep these parameters in mind.

If you’d like to utilise some pre-designed training sessions, consider trying any of the sets used in the research studies described above. I’ve also included several sample sessions for to spark your creativity, as well as the rational and guidelines to consider when creating your own (see table 4). You can shift the focus of the session to work more on maximal power or power endurance by manipulating the training variables. Both can be valuable additions to your training. See which version you respond to best.

If you’re new to resistance training in the pool, start with lower volumes to determine how your body reacts to the training. You can always do more later. Any sprint resistance training session should be proceeded by a warm-up similar to what you’d use for any high intensity training session.

Now that you have a basic idea of how to design a training session, where do these sessions fit in a weekly schedule of training and how often should they be performed? Further guidelines for incorporating resistance training are below. While resistance training can be a very important part of a swimmer’s training program, remember it’s not the only part. It should be balanced against the other training components, with each receiving relative priority at different times.

Resistance training guidelines

  • As with all resistance work, it should be included through the calendar year to ensure strength improves over time.
  • Perform resisted sprinting 1-3 times per week in addition to your regularly scheduled training.
  • The frequency at which resistance training is included will depend on the time of year, the events you target, and the training time you have available.
  • Focus on quality over quantity. Less is more!
  • Be sure to include progression and variety in your resistance programme.

Another important consideration is how to progress resistance training over time. Table 5 provides several options for progressing your training. While any of the options can be appropriate at any time, as competition dates get closer, the same peaking strategies used for regular training apply to resistance training in the pool. The focus should be on less volume, more rest, less resistance, and shorter distances. Further away from competition, you can increase the resistance, total volume, repetition distances, and lower the rest intervals.

Table 5: Training progression options
·        Increase the distance of the sprint while attempting to maintain velocity.

·        Decrease the distance while attempting to increase velocity.

·        Increase the resistance used during the sprint while attempting to maintain velocity.

·        Decrease the resistance used during the sprint while attempting to increase velocity.

·        Change the type of resistance employed.

·        Add paddles or fins to overload the limbs.

·        Increase the rest periods while attempting to increase velocity.

·        Decrease the rest periods while attempting to maintain velocity.

·        Slightly increase the volume.

·        Include contrast sets to practice switching from resisted to normal swimming.

·        Overload the upper or lower body by performing resisted pulling and kicking.

Summary of the key learning points

  • For swimming performance, force production is critical in the pool. A base of terrestrial strength can be a valuable addition to your swimming regiment, but only up to a point.
  • Too optimise strength development in the water, strength training should take place in the water.
  • The best way to improve strength in the water is through resisted swimming. Be creative and use whatever equipment you have available, or make your own!
  • As with terrestrial strength training, adjust your training to target the strength qualities you desire.
  • Quality is key; ensure optimal recovery within and between sessions, aiming to complete 1-3 strength sets per week depending on your goals and available training time.


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