Swimming Power: Relevance & Muscle Physiology - Part 1

By Deniz Hekmati

To me, there is one key element that is crucial for power development and maintenance. This component is often times overlooked, but it is also one of the most vital ingredients to humans from birth: proteins. Slipping through our everyday thinking, proteins are extremely crucial in DNA development, immune defense, and neuromuscular contractions.

In swimming, there are 5 major standout areas where power becomes a headline topics:

  1. Start
  2. Turn
  3. Stroke
  4. Underwater Kick
  5. Breaststroke Kick

The starts and turns are the two most significant swimming aspects that correlates with powerful lower body properties (Garcia-Ramos et al., 2016). They found that squat jumps at body weight (BW), BW + 25%, BW + 50%, BW +75%, and BW + 100% had positive impact on start-performance to 5M, 10M and 15M. Leg power also seems to have an effect on turn performance as well, especially coming out from the wall. Many coaches would argue that there is a 5th stroke, being under-water (UW) swimming. Although no direct literature exists on core power and UW speed, many would argue that some correlation may be seen if researched. Breaststroke is the only stroke where leg power is with certainty contributing to forward propulsion without much literature to back that statement up. I say this, because it is becoming more commonly accepted that the flutter kick in freestyle and backstroke acts more of a drag minimizer by upholding body position, before it helps with forward propulsion. On the other hand, the dolphin kick in butterfly will act and aid strongly during the recovery phase of the arms, leading to a smooth entry and a more powerful pull, although no direct literature exists to confirm that.

The most controversial of all the components is the upper body strength profiles and its effect on actual stroke power increase or time drops in swimming performance. This is an ongoing debate, as literature still is scarce on the true effects of either increased back or chest strength and its transfer to improved stroke length. Subsequently, there is only one equation to explain swimming power in form of speed:

Swimming Velocity = Stroke Length x Stroke Rate

Stroke Rate
The finesse of fast swimming is to find each individuals most optimal stroke rate (SR) for their races – the swimming coaches should be able to guide the swimmers to their best suited stroke rates. It has now been confirmed that a higher SR also leads to significantly increased metabolic demands (Morris et al., 2016). Therefore, be mindful of your stroke rate in practice, and in a race. In addition, swimming is a highly technical sport, where just small angle differences in the wrist, elbow, and shoulder joints can be either detrimental, or advantageous within each stroke in each race. Lastly, at a certain SR, stroke length (SL) gets compensated and power decreased.

Stroke Length
This is the variable that the strength coach has the utmost ability to positively affect with smart and sport specific programming. Further research is strongly encouraged in this area, especially looking at what the transfer of the movement actually applies to increased swimming speed or stroke power. Pešić and colleagues found a positive effect in freestyle stroke efficiency, and stroke length in breaststroke (2015). Other literature also exists that upper body strength profiles do not have any impact on stroke power. However, it is important to note that the older research also used old techniques to develop strength, and that an updated intervention might find something that correlates more strongly to SL development.

What is Power?

The power developed by a muscle is defined as the product of the load and velocity in a given movement:

Power = Load x Velocity

Hill Force Power VelocityRenowned physiologist, Dr. Hill (1938) developed very central principles around force and power production. More specifically, he found a relation between force-velocity, and power-velocity. Surely, a movement is slowed down when more load is added. Picture a squat, - you will be standing up slower with 100kg on your back compared to 50kg. Therefore, the most force is generated when you are moving the slowest (top two graphs). The above figures illustrate a model in rats with two different concentrations of potassium (K+) was used during incubation of the rat muscle (left vs. right graphs) (Pedersen, Nielsen, Ovegaard, 2013). When it comes to power, it has its own set of rules. Looking at graph C and D, you can see that the maximal power occurs somewhere around 30-40% of the maximal force production. So if your 1 repetition maximum is 100kg, you generate the most power closer to 30-40kg. One of the most powerful lower body movements that can be done is a pure body weight squat jump, because the speed at which the muscles are shortening is a very optimal speed for power. But if you start misusing and prescribing them in abundance, you may inhibit proper power adaptation.

Muscle Contractions
It all comes down to the proteins. A muscle contraction is also known as the sliding filament theory. In short, there are two acting key contractile proteins: actin and myosin. These two connect and together make power strokes that is the equivalent of a muscle contraction, as the release of ATP allows myosin to bind to actin.

Sliding Filament Theory

Take a second to let this sink in, and picture a swimming stroke. This cycle is happening thousands of times in different muscles including: internal rotator cuff muscles (subscapularis, supraspinatus, infraspinatus, and teres minor) latissimus dorsi, pectoralis minor, and triceps brachii. Depending on the individual athlete’s physiology, by-products, force generation, and pH sensitivity will differ considerably.

Power Influences

Fiber Types
Maximal power during a movement, such as the swim stroke, is determined by the contractile capacity of the muscles involved. The contractile capacity of a muscle is primarily influenced by fiber type composition (Cormie, McGuigan, & Newton, 2011). There are three main fiber types in humans—Type I, Type IIa, and Type IIx—which differ based on their contractile properties. Type I fibers are designed for extended use at low velocities (i.e. aerobic exercise). Type IIa and IIx fibers are characterized by high power outputs, velocities, and rates of force development and are suited for brief, powerful contractions (i.e., sprinting), but lower oxidative capacities, less capillary and mitochondiral density. Type IIa fibers have greater fatigue resistance than Type IIx fibers while Type I fibers are the most fatigue resistant (Schiaffino, 2010).

Histochemical and Immunochemical Properties
The myosin heavy chain (MHC) isoform—specific to each fiber type—determines the speed at which the actin filaments are displaced and thus determines the maximal unloaded shortening velocity (Vmax) of the fiber (Schiaffino, 2010). The difference in Vmax between fiber types is suggested to be the main determinant of maximal power output (Pmax) of a fiber (Lieber, 2010), with Vmax and Pmax increasing in the order of I<IIa<IIx (Schiaffino, 2010). Type II fibers have been shown to have a Vmax and Pmax three and four times greater, respectively, than Type I fibers (Faulkner, Clafin, & McCully, 1986) and research has consistently shown that Pmax is greater in muscles with a high percentage of type II fibers than muscles with a high percentage of type I fibers (Cormie et al., 2011).

It is important to understand as a coach that a considerable amount of difference exist between type I and type II fibers within the different muscle groups when looked under the microscope to evaluate the muscle “staining.” Histochemical properties evaluate MHC isoforms to better understand enzymatic activity in a molecular level. The most abundantly studied enzyme in the muscle is myosin ATPase and its staining during ATP hydrolysis.

A more recent and accurate way of evaluating the functionality of the muscle is to look at the various molecular isoforms of key muscle proteins (immunihistochemical properties). And this is where things get complicated. Depending on how cross-bridge interactions, the myosin controls the pH sensitivity of the ATP-splitting reaction. We now know that there are 4 different MHC; I, IIa, IIx, IIb (the small letters designates the heavy chains). If exclusively one heavy chain is detected in the muscle, it is considered to be a type I, which means that there is a substantial amount of fast twitch muscles that could potentially be found within one muscle group.

Levels Of Muscle

Diurnal Effects
Diurnal effects refer to daily changes in the body, such as hormonal secretion, body temperature, and metabolic demand. Deschodt and Arsac evaluated the difference in maximal cycling power and technical swimming abilities in eleven nationally competitive swimmers, and how it was different from morning and night (2004). A maximal 6-second sprint cycling test was done together with a 50M freestyle sprint. The tests were randomly performed at 8 AM, 1 PM, and 6 PM with 15h in between each.

Diurnal Effect In PowerThe figure  illustrates the difference in power between the three time frames, which held true for both the test (p < 0.01). A 7% gain in power was seen between morning and night in the cycle sprint. One of the reasons for this might be because of a higher rate of ATP turnover at night, which potentially could explain the difference. Interestingly, the morning showed a greater technical ability than evening. Since swimming competitions include morning and evening sessions, this information is valuable to know as a coach. Depending on the main emphasis of the workouts, these numbers should be considered when planning a training cycle.

Swimming Training on Muscle Fiber Type

While inherited factors account for approximately 45% of the variance in muscle fiber type (Simoneau & Boucard, 1995), muscles have a remarkable ability to adapt to use and disuse. Research has shown that MHC isoform transitions can occur with training. Endurance training causes an increase in Type I fibers with a concomitant decrease in Type II fibers (Schaub, Brunner, Von Schulthess, Neidhart, & Baumann, 1989; Trappe et al., 2006). And indeed, endurance athletes display a greater proportion of Type I fibers—69% —compared to recreationally active young men—41% (Malisoux, Francaux, & Theisen, 2007). On the other hand, resistance and plyometric training have been shown to induce a shift in fiber type towards Type IIa (Wildrick, Stelzer, Shoepe, & Garner, 2002; Andersen, Klitgaard, & Saltin, 1994; Malisoux et al., 2006). Resistance and plyometric-trained individuals express Type II fiber proportions of 56% and 42%, respectively (Malisoux, Francaux, & Theisen, 2007).

With regards to sprint training, a number of studies consisting of cycling or running sprints lasting less than or equal to 30 seconds performed approximately three days per week have revealed changes in fiber type proportions towards Type II (Allemeier et al., 1994; Dawson et al., 1998; Esbjornsson et al., 1993; Jansson, Esbjornsson, Holm, & Jacobs, 1990; Jacobs, Esbjornsson, Sylven, Holm, & Jansson, 1987). Even so, other sprint-training investigations (Esbjornsson-Liljedahl, Holm, Sylven, & Jansson, 1996; Linossier, Denis, Dormois, Geyssant, & Lacour, 1993; Simoneau et al., 1985) have showed shifts in fiber proportions towards Type I; however, these studies used sprints of excessive duration and/or frequency with short recovery periods between reps—highlighting the sensitivity of fiber type plasticity to training design. Research by Esbjornsson et al. (1993) exemplifies the effect frequency has on muscle fiber type transitions. Six weeks of ten-second cycle sprints with 50 seconds rest between, three times per week, resulted in a significant fiber shift towards Type IIa. In a seventh week, Esbjornsson et al. (1993) increased cycling frequency to 14 times per week, resulting in a shift in fibers towards Type I. Research by Esbjornsson et al. (1993) not only demonstrates the sensitivity of fiber adaptations to frequency but also the rapidity with which fibers shifts occur. Thus, from examination of the sprint-training literature, it can be concluded that less frequent, lower volume training with an emphasis on rest and recovery are key to optimal type II fiber adaptations.

It is interesting to note that previous research investigating fiber type proportions in swimmers have revealed 67% Type I fibers (Costill, et al., 1991; Fitts et al.,1989; Houston et al., 1981; Trappe et al., 2000) similar to the proportions of endurance athletes. The high type I fiber proportions in swimmers suggests that traditional swim training may not be optimal for the sprint-swim events if maximal power output is the goal. Only a few studies have examined the effect of swim volume on muscle fiber type and performance.

Fitts et al. (1989) examined the effect of ten weeks of normal swim training—90-min per day, five days per week, totaling 4,266-m per day—on the adaptations to muscle fibers of 12 male collegiate swimmers. The swim training resulted in significant decreases in Type II fiber size and Vmax. They then investigated the muscle fiber response to ten days of intensified swim training—two sessions per day of 90-min each, totaling 8,970-m per day. It is customary for many swimmers to engage in intensified training periods, the conventional idea being that these periods provide further increases in adaptations necessary for improved swim performance. Fitts et al. (1989) found no improvement in swim performance following the ten-day intensified training, nor were there additional effects on aerobic enzyme capacities—an adaptation which would be expected to be a significant purpose for the intensified training. Moreover, Type II fiber Vmax was further decreased and a leftward shift of the force-velocity curve was observed for each subject.

Houston et al. (1981) divided ten collegiate swimmers into two groups: a moderate-intensity group—swimming distances of 183-437-m with short rest between sets, for a total of 3,200-m per day—and a high-intensity group—swimming distances of 23-183-m with long rest between sets, for a total of 1,650-m per day. Both groups trained for 6.5 weeks, approximately four days per week, for 90-min each session. Results showed similar adaptations in VO2max, aerobic enzyme activities, and muscle fiber composition with no difference in swim performance at 23-, 91-, or 457-m between the two groups.

Costill et al. (1991) studied the effect of a reduced volume swim-training program on swimming endurance, power, and performance. For six weeks, 24 male collegiate swimmers were split into two groups: a “short” group—swimming one 90-min session five days per week, totaling 4,950-m per day—and a “long” group—swimming two 90-min sessions, one in the morning and one in the afternoon, five days per week, totaling 9,435-m per day. During the six weeks of training, 25-yd swimming velocity increased in the “short” group and decreased in the “long” group. No differences were observed in exercising blood lactate, heart rate, or glycolytic and aerobic enzyme activities between the two groups during the six weeks of varied training. Additionally, the two groups resumed the same training following the six-week intervention for an additional 14 weeks. Swimming power, endurance or performance did not differ between the groups after 14 weeks of the same training. It was thus concluded that the increased volume and frequency of training experienced by the “long” group provided no additional benefit over the “short” group. Questioning the efficacy of the type of swim training conducted in the study, Costill et al. (1991) state, “Since the majority of competitive swimming events lasts less than 3 min, it is difficult to understand how training at speeds that are markedly slower than competitive pace for 3-4 h/d will prepare the swimmer for the supramaximal efforts of competition.”

Trappe et al. (2000) examined the effect of a 21-day taper (reduction in swimming volume) on contractile properties of Type I and Type II fibers of six male collegiate swimmers. Prior to the taper, the athletes were swimming 6,200-m per day for five months. Swim volume was systematically reduced during the taper to 2,000-m per day during the last two days. The reduced volume resulted in improved swim performance of 4%, and a 17% and 13% increase in whole muscle power during a swim bench test and during a tethered isokinetic swim power test, respectively. Type II fiber diameter increased 11%, with 67% increase in shortening velocity, and 2.5-fold increase in power. The results by Trappe et al. (2000) demonstrate that a reduction in swim volume has significant effects on the maximal power output of Type II fibers and is associated with improved swim performance


Swimming is a power sport. Therefore, each exercise in the weight room should be performed with a deliberate and fast acceleration while trying to maintain the highest speed possible throughout the muscle shortening phase (concentric contraction), no matter the load. Proteins and underlying principles of muscle physiology make up for crucial elements of fast swimming. This is a very novice introduction to how deep muscle physiology research has come.

Additionally, this might explain the birth of Ultra-Short Race-Pace Training as well. If you keep training at race speed, by only use the relevant muscle fibers and motor units – more than likely – the muscle fibers will slowly start shifting towards what is exactly needed in your swimming events.

Understanding the deep physiology will give the coach an upper hand in delivering the best possible workouts. If you don’t have access to a coach, we would love help you drop some time this coming winter and next summer – do not hesitate to apply for a strategy session to see if you would be a good fit for our Swimmer’s Edge Program!


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