Abstract
Context:
Ankle plantarflexion is thought to play an important role in swimming performance; thus, coaches and swimmers often seek ways to increase range of motion (ROM) in the ankles.
Objective:
To assess whether osteopathic manipulative treatment (OMT), specifically applying the muscle energy technique (MET) principle of post–isometric relaxation, increases ankle plantarflexion and therefore improves swimming performance.
Methods:
Healthy young male and female competitive swimmers were randomly assigned to either a control, sham, or MET group. At baseline, ankle plantarflexion was measured via goniometer, and a 25-yard flutter kick swim with a kickboard was timed. After receiving the ascribed intervention, the ankle plantarflexion measurements and timed flutter kick were repeated. The initial plantarflexion measurement was retrospectively used to determine the presence of somatic dysfunction, by way of restricted motion, with reference to expected normal ranges based on age and gender. Paired t tests were used to analyze the pre- to postintervention changes in ROM and flutter kick speed within each group.
Results:
Fifty-five swimmers (32 girls and 23 boys; mean age, 12 years) participated in this study. Sixteen participants were in the control group, 17 in the sham group, and 22 in the MET intervention group. Among participants with restricted ROM, those in the MET group showed a statistically significant increase in ankle plantarflexion for the left and right ankles (P=.041 and P=.011, respectively). There was no significant difference in ROM of the control or sham groups. For flutter kick speed, there was no significant pre- to postintervention difference in any group.
Conclusion:
Although a single application of MET, using post–isometric relaxation, on participants with restricted ROM immediately significantly increased swimmers’ ROM for bilateral ankle plantarflexion, it did not immediately improve their swimming performance.
Winners of swimming events are sometimes decided by mere fractions of a second. Thus, coaches and swimmers seek opportunities to maximize efficiency and minimize potential barriers to improved speed. One area that coaches and swimmers seek to improve is ankle flexibility, especially plantarflexion. Various modalities of stretching, including static, dynamic, and proprioceptive neuromuscular facilitation, are used in the athletic environment.
1,2 However, our search of the literature in May 2016 (PubMed and EBSCOhost) and Feb 2017 (Osteopathic Medicine Digital Repository) uncovered no studies that examined the use of osteopathic manipulative treatment (OMT), or specifically muscle energy technique (MET), as a tool for effectively increasing the ankle's plantar flexion range of motion (ROM) in swimmers. Furthermore, we discovered no studies that examined the effect of MET on swimming performance.
The front crawl (or freestyle) stroke in swimming uses a flutter kick in the lower extremities. The flutter kick consists of 2 alternating motions: the upbeat kick and the integral downbeat kick. The upbeat kick functions mainly as a stabilizer of the body, while the downbeat kick generates propulsion through the water.
3 In the downbeat kick, the hip slightly flexes, the knee extends, and the ankle plantarflexes. The opposite then occurs during the upbeat kick.
Optimal swimming technique is determined to a great extent by the flexibility of the ankles.
4 Greater ankle plantarflexion is associated with less resistance on the downbeat kick, producing more propulsion with less effort,
5,6 and freestyle kick performance depends on ankle joint flexibility.
7 When the ability to plantarflex during the downbeat kick is restricted, drag is increased and less water is displaced backward, resulting in less forward propulsion.
8
Muscle energy technique has been shown to increase the ROM in multiple joints.
9-11 In the present pilot study, we tested the hypotheses that MET, using the principle of post–isometric relaxation (PIR), will increase ankle plantarflexion and result in faster swimming speed using the flutter kick.
Competitive swimmers, both male and female between the ages of 8 and 17 years, were recruited from Pittsburgh-area swim teams via an email advertisement. Two weeks before the study, the swim coaches distributed a handout prepared by the investigators to parents during practice. One week before the study, an email prepared by the investigators was sent by the coaches to the email addresses of the children on their listserves. The email had consent and asset forms attached; these forms were also available in hard copy at the time of the study. To ensure a safe rehabilitation window and to allay concerns of potential harm, swimmers were excluded if they had a history of ankle sprain in the previous 2 months, ankle fracture in the previous 3 months, or any previous ankle fusion surgery. Parents or legal guardians were required to sign an informed consent form, and each child was required to sign an assent statement, as stipulated by the study protocol, which was approved by the institutional review board at the Philadelphia College of Osteopathic Medicine.
This pilot study was prospective, randomized, controlled, and partially double-blinded. Each participant was excused by the coach from a portion of his or her regular swim practice to participate in the study, which took about 10 to 20 minutes. Participants were randomly assigned to 1 of 3 groups: control, sham, or MET. Each participant attended 1 study session.
Throughout the study, investigator 1 (D.E.S.) recorded the demographics, performed and documented the ankle measurements, documented the flutter kick times as reported to her, and performed the assigned intervention. This investigator was blinded as to which participants would be determined to have restricted ROM. Investigator 2 (B.N.V.) timed the kicks and reported them; she was unaware of the groups to which each participant had been assigned or the measurements obtained by investigator 1.
The protocol described in the following paragraphs was followed for all participants.
Table 2 summarizes the change in the ROM of bilateral ankle plantarflexion, as measured before and after the intervention.
Table 2.
Effects of Post–Isometric Relaxation on Ankle Plantarflexion and Timed Flutter Kick in Pediatric Competitive Swimmers: ROM Before and After Intervention by Group
| ROM of Left Ankle | ROM of Right Ankle |
| Group | Before | After | Δa | P Valueb | 95% CI | Before | After | Δa | P Valueb | 95% CI |
| Whole Group | | | | | | | | | | |
| Control (n=16) | 47.094 | 47.844 | +0.750 | .693 | −4.721 to 3.221 | 46.375 | 46.750 | +0.375 | .796 | −3.404 to 2.654 |
| Sham (n=17) | 52.618 | 50.647 | −1.971 | .382 | −2.675 to 6.616 | 49.324 | 51.294 | +1.97 | .182 | −4.964 to 1.023 |
| MET (n=22) | 42.659 | 46.568 | +3.909 | .046 | −7.742 to −0.076 | 43.955 | 50.432 | +6.477 | .004 | −10.690 to −2.264 |
| Restricted ROM Subgroup | | | | | | | | | | |
| Control (n=12) | 43.000 | 44.250 | +1.250 | .594 | −6.263 to 3.763 | 42.292 | 42.542 | +0.250 | .896 | −4.353 to 3.853 |
| Sham (n=10) | 45.300 | 46.700 | +1.400 | .650 | −8.150 to 5.350 | 42.700 | 45.200 | +2.500 | .164 | 1.230 to −6.230 |
| MET (n=20) | 40.775 | 45.125 | +4.350 | .041 | −8.500 to −0.200 | 42.300 | 48.575 | +6.275 | .011 | −10.924 to −1.626 |
| Nonrestricted ROM Subgroup | | | | | | | | | | |
| Control (n=4) | 59.375 | 58.625 | −0.750 | .838 | −9.974 to 11.474 | 58.625 | 59.250 | +0.625 | .680 | −5.001 to 3.751 |
| Sham (n=7) | 63.071 | 56.286 | −6.786 | .027 | 1.085 to 12.486 | 58.786 | 60.000 | +1.214 | .661 | −7.654 to 5.226 |
| MET (n=2) | 61.500 | 63.00 | +1.500 | .500 | −20.560 to 17.560 | 60.50 | 69.00 | +8.50 | .182 | −40.270 to 23.270 |
Table 2.
Effects of Post–Isometric Relaxation on Ankle Plantarflexion and Timed Flutter Kick in Pediatric Competitive Swimmers: ROM Before and After Intervention by Group
| ROM of Left Ankle | ROM of Right Ankle |
| Group | Before | After | Δa | P Valueb | 95% CI | Before | After | Δa | P Valueb | 95% CI |
| Whole Group | | | | | | | | | | |
| Control (n=16) | 47.094 | 47.844 | +0.750 | .693 | −4.721 to 3.221 | 46.375 | 46.750 | +0.375 | .796 | −3.404 to 2.654 |
| Sham (n=17) | 52.618 | 50.647 | −1.971 | .382 | −2.675 to 6.616 | 49.324 | 51.294 | +1.97 | .182 | −4.964 to 1.023 |
| MET (n=22) | 42.659 | 46.568 | +3.909 | .046 | −7.742 to −0.076 | 43.955 | 50.432 | +6.477 | .004 | −10.690 to −2.264 |
| Restricted ROM Subgroup | | | | | | | | | | |
| Control (n=12) | 43.000 | 44.250 | +1.250 | .594 | −6.263 to 3.763 | 42.292 | 42.542 | +0.250 | .896 | −4.353 to 3.853 |
| Sham (n=10) | 45.300 | 46.700 | +1.400 | .650 | −8.150 to 5.350 | 42.700 | 45.200 | +2.500 | .164 | 1.230 to −6.230 |
| MET (n=20) | 40.775 | 45.125 | +4.350 | .041 | −8.500 to −0.200 | 42.300 | 48.575 | +6.275 | .011 | −10.924 to −1.626 |
| Nonrestricted ROM Subgroup | | | | | | | | | | |
| Control (n=4) | 59.375 | 58.625 | −0.750 | .838 | −9.974 to 11.474 | 58.625 | 59.250 | +0.625 | .680 | −5.001 to 3.751 |
| Sham (n=7) | 63.071 | 56.286 | −6.786 | .027 | 1.085 to 12.486 | 58.786 | 60.000 | +1.214 | .661 | −7.654 to 5.226 |
| MET (n=2) | 61.500 | 63.00 | +1.500 | .500 | −20.560 to 17.560 | 60.50 | 69.00 | +8.50 | .182 | −40.270 to 23.270 |
×
Among participants who received MET, the whole group and those in the subgroup of restricted ROM had statistically significant increases in bilateral ankle plantarflexion (whole group: P=.046 on the left and P=.004 on the right; subgroup of restricted ROM: P=.041 on the left and P=.011 on the right). Among participants in the control and sham groups, the whole groups and subgroups of restricted ROM did not demonstrate any statistically significant change in plantarflexion from before to after the intervention.
In the subgroup of nonrestricted ROM, there was no significant change in ankle plantarflexion, except in the left ankle of the sham group, which demonstrated significantly less ROM after the sham intervention (a loss of 6.786°; P=.027)
At the outset of this study, we applied an interventional protocol to all participants within randomly assigned groups, blinding the investigators as to whether participants were symptomatic or asymptomatic with regard to restriction of ankle plantarflexion, mitigating the potential bias of treating one participant differently from another. For those participants receiving MET, using the principle of PIR, the technique was applied as a way to gently stretch myofascial structures, to allow for increased plantarflexion, and to observe how this functional gain affects flutter kick performance, which was measured in seconds over 25 yards.
In the clinical setting, the indication for OMT is the diagnosis of somatic dysfunction. We retrospectively diagnosed somatic dysfunction using the most objective criterion—ROM—referenced against a national guideline for normal ROM.
15 Once we had subgroups of individuals with somatic dysfunction (restricted ROM) and without somatic dysfunction (nonrestricted ROM), we were able to compare these subgroups with each other and with the whole group.
After MET, there was a statistically significant increase in the ROM of both ankle joints in both the whole group and the subgroup of restricted ROM, with no change in the sham or control interventions. These findings supported our hypothesis that MET, using the principle of PIR, will significantly improve plantarflexion, notably distinguishing the presence of somatic dysfunction via restricted ROM.
When looking at the raw data points, the 9- and 10-year-olds (the youngest in the group) were the participants whose left ankles lost ROM (mean, 11.5
o), whereas the older participants (age 13 years) all stayed the same or gained ROM. This finding could be enough to skew the statistics. This loss did not occur on the right side, except in one of the 9-year-old participants. Our speculation is that the younger participants may not have complied properly with the instructions to plantarflex to the comfortable full range when the left ankle was measured (the first ankle of the 2 to be measured in the protocol). Regardless of the reasoning, however, the small subsample provides poor power for this statistical outcome to be meaningful. There was no change, by way of increased plantarflexion, with the control, sham, or MET interventions in the subgroup of nonrestricted ROM. Although this finding may be because these participants’ ankles did not have somatic dysfunction because they were not initially restricted in their ROM, it is more likely that the numbers were too small to be powered enough to definitively demonstrate that assertion. In a future study, the numbers in the subgroup of nonrestricted ROM would need to be higher. Looking at the performance data for flutter kick time, in both the whole group and the subgroup of restricted ROM, the participants who received MET were actually slower on postintervention flutter kick than the control or sham groups. However, none of the differences was significant. These findings rejected our hypothesis that MET, using the principle of PIR, will improve flutter kick performance and reduce swim time. Similar results have occurred in studies that observed decreased performance of swimming, jumping, or sprinting when using methods of muscle stretching that differ from PIR—namely, static stretching and proprioceptive neuromuscular facilitation stretching.
1,16,17
For the subgroup of nonrestricted ROM, the numbers are, again, too small to make any statistical conclusions on swimming performance in participants who have ankle plantarflexion within or above the normal range.
Previous studies have shown that MET is effective at increasing joint ROM.
9-11 What is less clear is the mechanism by which this increased joint ROM occurs. Traditionally, we speak of a muscle relaxation that occurs after an isometric muscle contraction, whereby there is a refractory period in which the muscle may be passively lengthened without insult to the neuromuscular apparatus.
18 However, there may be a variety of neurologic and biomechanical mechanisms that affect the change we see with MET.
19
In the present study, the intervention (control, sham, or MET) was applied directly before the participants were given a physical task (the second timed flutter kick). In the whole group and subgroup of restricted ROM (the groups whose numbers were sufficiently powered to make conclusions), we theorize that the MET participants may have been more fatigued by the PIR, thus slowing them down on the second timed swim. Although we did not evaluate this factor, we retrospectively postulated that high-energy phosphates were depleted with the PIR and that there was not enough recovery time after the intervention to reap the benefit of having increased ROM. Bishop supports a similar theory when addressing warm-up protocols before sports activity.
20 Future studies will provide a longer recovery period before the second timed swim to test the energy-depletion concept with PIR.
There are a few other notable limitations of this study, some of which may have especially affected performance measures. Beginning with the participants themselves, the age and maturity level of the younger participants seemed to affect their ability to follow instructions without distraction. Furthermore, the participants were at different strength and skill levels with regard to their swimming abilities, which may have affected performance variability. Some participants had already been swimming for close to an hour before being evaluated for the study, which may have affected levels of fatigue, hindering subsequent performance.
The small sample size in this pilot study limits the generalizability of our findings. A larger study population with participants stratified by age, gender, and skill level would address these potential influences on performance variability.
It would be useful to find participants who have a history of ankle trauma (nonacute sprain/strain, healed fracture, or uncomplicated recovery from ankle surgery), as these participants would be ideal candidates to best benefit from MET. An additional modification of the experimental design could include having separate investigators to document ankle measurements, perform the MET, and measure swim times to eliminate the potential for bias. Because each participant underwent only a single session with a single set of evaluations for ROM and flutter kick time, we are uncertain as to the effects of MET, using PIR, over subsequent days or weeks. Furthermore, other biomechanical factors contribute to swimming performance. In particular, arm strength and ROM are obvious and critical components of swim speed. In our study, the action of the arms was eliminated from the swimming stroke to decrease confounding factors on the effect of ankle ROM. However, controls such as this are not realistic for swimming competitions.
Finally, we chose to use MET's principle of PIR to increase ankle plantarflexion and ROM. Post–isometric relaxation was selected mainly because it can be taught to swimmers, coaches, and trainers. Other types of OMT, such as soft tissue technique and balanced ligamentous tension, can be tested for their effects on ROM and swim time.
We thank Jane Z. Dumsha, PhD, Chief Research Operations Officer, and Mindy George-Weinstein, PhD, Professor and Chief Research and Science Officer, both at the Philadelphia College of Osteopathic Medicine, for their design input and critical editing of this manuscript.