An 18-Day Stretching Regimen, With or Without Pulsed, Shortwave Diathermy, and Ankle Dorsiflexion After 3 Weeks

Abstract

Context: The amount of retained ankle flexibility gains and the effects of diathermy on those gains are unclear.

Objective: To determine the retention of flexibility 3 weeks after an 18-day stretching regime and the effect of pulsed, shortwave diathermy on that retention.

Design: We used a 2x4 factorial with repeated measures on day (1, 19, 24, and 39). The other independent variable was treatment (stretch only versus diathermy and stretch). The dependent variable was ankle-dorsiflexion angular displacement as measured on a digital inclinometer.

Setting: Therapeutic Modality Research Laboratory.

Patients or Other Participants: 23 healthy college-aged volunteers (8 males, 15 females; age = 22.7 ± 2.1 years, height = 171.1 ± 8.8 cm, mass = 70.4 ± 13.5 kg).

Interventions: All subjects performed 3 weeks (not including weekends) of low-load, prolonged, long-duration stretching. One group performed stretching only; the other group also received diathermy.

Main Outcome Measure(s): After an 18-day stretching regime and 7-day retention study, subjects returned 14 days later for the 3-week retention measure. The angle of inclination from the posterior Achilles tendon to the sole of the shoe near the heel was measured on each treatment and test day.

Results: Regardless of group (F_1,21 = 0.74, P = 0.40), the flexibility gained between days 1 (99.7 ± 4.0°), 19 (102.9 ± 5.8°), and 24 (105.0 ± 6.2°) were maintained at day 39 (104.8± 7.2°) (P < .05).

Conclusions: Flexibility gains in normal ankles with 3 weeks of training were retained for at least 3 weeks after training ceased. The application of pulsed, shortwave diathermy during stretching did not appear to influence the chronic retention of flexibility gains in normal subjects.

Ankle flexibility researchers have focused mainly on short-term gains of various stretching regimen factors, such as type of stretching,^1–4 duration of stretching,^5–7 stretching frequency,^7,8 stretching load,^9,10 and tissue heating^11–17 in healthy subjects. Even though this information is practical, it is also important to recognize if the gains are retained after the regimen has ended. To date, only 2 groups have reported on retention: the first¹⁸ reported “chronic” results (21 days after the conclusion of a hamstring stretching regimen) and the second¹⁷ reported on the “long-term” effects (6 days) after a triceps surae stretching regimen. Although they reported that the gains were maintained, there was a trend toward baseline in the “chronic” study.¹⁸

Whatever the effect of diathermy on tissue elongation, in the first retention study,¹⁸ the effect was not considered because the subjects gained flexibility regardless of whether diathermy was administered. The lack of diathermy effect might have been because the stretching protocol was performed after, rather than in conjunction with, the diathermy,¹⁹ which may have reduced diathermy's effect on tissue elongation. Hence, in the second study,¹⁷ investigators began the stretching during the diathermy application. Similarly, they concluded that diathermy positively affected short-term gains in range of motion. Moreover, the second retention study illustrated that diathermy's positive effects on tissue elongation continued for at least 7 days after the regimen. The difference in retention between these 2 studies may have been because of the different body areas studied, when the diathermy was administered, and the interval until the retention measures. Our purpose, therefore, was to determine if flexibility gains in groups of similar, healthy subjects were maintained 21 days after the regimen and if the additional flexibility gains induced by pulsed, shortwave diathermy and stretch were maintained better than stretching alone.

METHODS

This investigation is an extension of the aforementioned ankle study,¹⁷ which involved subjects from 3 of the 5 original groups. We used a 2 by 4 factorial design with repeated measures on the last factor. The independent variables were treatment (stretch only and diathermy and stretch) and day (1, 19, 24, and 39). The dependent variable was right ankle angular displacement as measured by an inclinometer. The same certified athletic trainer collected all the data.

Subjects

In the preceding study,¹⁷ no difference was detected between the diathermy and stretch (n = 8) and the diathermy and stretch followed by ice (n = 9) groups, so we recruited these subjects along with the previous stretch-only group (n = 11). Of the 28 previous subjects, 23 (15 females and 8 males; mean age, 22.7 ± 2.1 years; mean height, 171.1 ± 8.8 cm; mean mass, 70.4 ± 13.5 kg) were measured on day 39. Of the 5 who were not included in this study, 3 stated that they would be unavailable and 2 subjects did not report for the study. Therefore, we studied 11 subjects in the stretch-only group and 14 subjects in the diathermy and stretch group.

Again, the recruited volunteers were healthy college students who did not engage in flexibility or strength training of the right triceps surae muscle, did not have allergies to cold medication or a right lower leg injury that would adversely affect ankle range of motion, and were not pregnant. Moreover, subjects were instructed not to change their daily routines. This study was approved by the University Human Subjects Review Board.

Instruments

We measured angle of inclination to ankle-dorsiflexion end range of motion to the nearest degree with a Dualer Electronic Inclinometer (JTech Medical Industries, Heber City, UT). According to the manufacturer, this electronic inclinometer uses eccentric encoding wheels that are accurate to ±1°, with a repeatability of ±1°. Manufacturer's instructions were followed at all times to ensure this accuracy. To quantify our measurement reliability (r = 0.99), we compared the 14 daily pretreatment measures to posttreatment measures of the no-treatment group (n = 8) in the original study.

Procedures

Subjects reported to the Therapeutic Modality Research Laboratory dressed in gym attire for 16 days of testing, which consisted of 3 weeks of stretching excluding weekends (days 1 to 18) and 6 and 21 days after the end of the regimen (days 24 and 39, respectively). The first session consisted of familiarizing and screening the subjects, obtaining informed consent, randomizing to treatment group, setting up for the measurements, and collecting data. The subsequent days were for data collection only. Measurements were taken before and after each day of treatment and on days 6 (day 24) and 21 (day 39) after the stretching regimen. The low-load, prolonged (throughout several days), long-duration (lasting longer than 1 minute) stretching regimen was intended to create larger changes in range of motion than other stretching regimens.¹⁷

In an attempt to ensure measurement consistency, we had subjects lie prone on a padded table with approximately the distal one third of the right lower leg exposed and hanging over the end of the table so that the line of pull of a dorsiflexion tension rigging was in alignment with the lower leg's sagittal plane. We used a permanent ink pen to mark a line 10 cm superior to the middle of the lateral malleolus on the posterior aspect of the right calf. This site was chosen because of its ease of access and repositioning and surface stability. Another mark was placed on the smoothest part of the plantar aspect of the shoe's heel. With this shoe landmark, we again had easy access, could reposition the inclinometer more easily, and had a more stable surface to measure. In addition, the subjects wore the same shoes each day, which reduced the likelihood that the measurement and stretching influenced the mid- and rear-foot motions. We re-marked these areas each time, and the subjects were asked to make sure these marks were not worn off and to wear the shoes as little as possible. Because we were interested in the effects of treatment in a fully repeated-measures design, using anatomical landmarks did not largely concern us. Therefore, the measures reported did not have any anatomical importance but did indicate change in angular displacement.

Once all marking and positioning were performed, we secured the subjects to the plinth with strapping across the lower lumbar area and asked them to relax while approximately one third of the subject's body mass was attached to the tension rigging (Figure 1). The amount of tension mass was determined during pilot testing in which subjects reported comfort levels during a 10-minute stretch using a selection of set absolute masses. These data indicated that a relative mass, approximately one third of the subject's mass, would be tolerated. Moreover, we believed that this amount of mass would produce enough force to elongate the calf musculature to end range and induce a stretch. Lastly, this load was considered to be low enough that it could be applied for long periods; longer-duration static stretching enhances gains.⁹

Figure 1. Treatment and testing setup with tension mass attached.

Immediately after attaching the tension mass, the inclinometer was centered over the posterior calf mark and zeroed (Figure 2A). Once zeroed, the inclinometer was positioned at the heel mark on the shoe (Figure 2B) and briefly allowed to stabilize before recording began. This measure served as the pretreatment measurement. The occasional stopwatch measurement of elapsed time between the attachment of the tension mass and the time the measurement was recorded was less than 30 seconds.

Figure 2. Zeroed position (A) and measurement position (B).

After the pretreatment measurement, the subjects in the stretch-only group had the tension force attached for 10 minutes. The group that received heat and stretching in this study was a combination of 2 of the original study's groups. One group remained in position without the tension attached for 15 minutes of a 20-minute diathermy treatment. To induce heating, one head of a Megapulse shortwave diathermy machine (Accelerated Care Plus Corp, Sparks, NV) was placed over a towel-dried calf near the triceps surae musculotendinous junction (Figure 3). The machine housed a 200-cm² induction coil, operating at a frequency of 27.12 MHz 2 cm from the faceplate. Settings were 800 bursts per second, 400-μs burst duration, and 800-μs interburst interval, with a peak root mean square amplitude of 150 W per burst and an average root mean output of 48 W. The tension mass was reattached for 10 minutes, beginning with the last 5 minutes of heating. The other group from the original study that was combined to form our heat-and-stretch group had a 1-kg ice bag placed on top of the calf during the last 5 minutes of stretching. Because the previous results¹⁷ showed that the ice application did not have any effect on the measures, we felt secure in combining this group with the original heat-and-stretch group. In addition, the combination of the 2 original groups into 1 heat-and-stretch group for this study should have strengthened our ability to detect treatment and time effects. Immediately after the treatment, a posttreatment measure was recorded using the aforementioned measurement procedures.

Figure 3. Pulsed shortwave diathermy setup.

Data and Statistical Analysis

The data were summarized by measurement timing (pretreatment, posttreatment), treatment, and day (Table 1). We used the first day's pretreatment measure as a beginning measure, and to establish an endpoint of training and the baseline for retention, we estimated a day 19 measurement. The day 19 measurement was calculated for each subject by subtracting the average overnight range-of-motion loss during the last week of training (Table 2) from the day 18 posttreatment measurement. By calculating this day 19 measurement, we removed any influence of the last day of stretching and its carryover.¹⁸

Table 1. Ankle Angular Displacement (Mean ± SD).

Table 2. Overnight Angle Changes During the Last Week of the Treatment Regimen (Mean ± SD).

We used a 2 by 4 repeated-measures analysis of variance to detect group and time differences and the Newman-Keuls multiple comparisons test for post hoc testing. The Geisser-Greenhouse method was selected to adjust for the violation of covariance matrix circularity. The statistical significance level was set at .05 before testing, and NCSS 2000 software (Number Cruncher Statistical System, Kaysville, UT) was used for all data summarization and testing.

RESULTS

The violation of circularity (Geisser-Greenhouse method: df = 8, P = .00003) regarding the treatment-by-day interaction did not influence its lack of effect on the measures (Geisser-Greenhouse method: F_3,63 = 1.91, P = .18, 1 − β = 0.26). Therefore, it can be clearly stated that the changes across days (F_3,63 = 26.78, P < .00001, 1 − β = 1.00) were similar between the 2 groups (F_1,21 = 0.74, P = .40, 1 − β = 0.31). Further post hoc testing (Newman-Keuls: alpha = .05, df = 63, mean square error = 4.3) revealed angular increases from day 1 (99.7° ± 4.0°) to day 19 (102.9° ± 5.8°) and from day 19 to day 24 (105.0° ± 6.2°). Moreover, all these increases were maintained on day 39 (104.8° ± 7.2°) (Figure 4).

Figure 4. Combined groups (stretching only and diathermy plus stretching) dorsiflexion angular displacement (°) measures by day. Day 1 < day 19 < days 24 and 39, P < .05.

DISCUSSION

Our results agree with, and extend, our previous report¹⁸ that flexibility is retained for 3 weeks after a stretching regimen. Differences between the studies included (1) the length of the regimen, (2) the duration each stretch was maintained, (3) the load used to produce tension, (4) the timing of when the tension was applied relative to the diathermy treatment length, (5) the body area tested, (6) the style of measurement, (7) the amount of range of motion possible, and (8) the different potential for developing flexibility. Still, we can have more confidence that flexibility will be retained after training.

In the only other long-term retention study,¹⁸ which also was a follow-up to a diathermy investigation,¹⁶ subjects were assigned to a stretching or rest group. The stretching group included subjects who were either treated with diathermy or not treated. Therefore, the retention of the range-of-motion gains may have been due to a diathermy effect on the treated subjects. The concept of a delayed effect of diathermy in enhancing retention became apparent when Peres et al¹⁷ reported positive diathermy effects 6 days after the end of treatment. Reasons for the delayed gains may have included reductions in muscle guarding, changes in subject activity levels, beginning new activities, or timing of activities. Because we tested the same subjects for our long-term retention measure, some of the same excitement or changes due to the end of the winter academic semester may have been present, although the subjects did not comment on them, even though we asked about habit changes. In a more recent study,¹⁹ shortwave diathermy combined with stretching enhanced range-of-motion gains more than stretching alone. However, the treatments did not differ in the amount of range of motion lost in the next 3 days. Even though these latest findings support our findings that diathermy does not influence retention, they prompt questions about the pattern of retention measures after training. Let us not forget that the 2 studies differed in many of the aforementioned variables. Therefore, the idea that diathermy while stretching improves flexibility retention more than stretching alone is still debatable.

CONCLUSIONS

Flexibility gains at the ankles of young, healthy people through 3 weeks of training were retained for at least 3 weeks after training ceased. The combination of pulsed shortwave diathermy with low-load, long-duration stretching did not influence the 3-week retention of flexibility gains any more than the stretching alone.