Improving one’s range of motion (ROM) has primarily been attempted through various stretching methods as part of physical fitness and rehabilitation programs with the intention of improving performance and reducing risk of injury (1–5). A variety of stretching methods including static stretching (SS), ballistic stretching, dynamic stretching, and proprioceptive neuromuscular facilitation can be used to increase ROM (6–8). In addition, an active warm-up can increase ROM (1,9–11). Because of its applicability to a wide range of clinical and nonclinical populations as well as its ease of use and safety, SS is probably the most common form of flexibility training used to improve ROM (12–17). The magnitude of the impact of stretching has on ROM is likely influenced by the muscle group(s) used during the flexibility training.
Several studies have evaluated the acute change in ROM due to SS. In a recent systematic review, Behm et al. (18) concluded that SS, proprioceptive neuromuscular facilitation, and dynamic stretching were all equally effective at acutely increasing ROM. Konrad et al. (12) reported a 4.3% increase in dorsiflexion ROM after police cadets completed four sets of 30 s of SS. Morse et al. (19) reported a 16.4% acute increase in dorsiflexion ROM after recreationally active men completed five sets of 60 s of SS, with the maximum dorsiflexion angle being reassessed after each set. Taniguchi et al. (20) reported a 30.7% increase in dorsiflexion ROM after five sets of 60 s of SS. Therefore, the acute change in dorsiflexion ROM could be affected by stretching intensity and stretching duration.
SS is an effective method for inducing long-term changes in ROM. Konrad and Tilp (21) reported 17.5% increase in dorsiflexion ROM after 6 wk of SS, which included five sessions per week with four sets of 30 s of stretching per session, in healthy police cadets. Hayes et al. (22) reported a 42.25% increase in dorsiflexion ROM after healthy volunteers completed 6 wk of SS, which included five sessions per week with each session containing three stretches performed for five sets of 30 s. It seems that total duration of stretching per session and total number of sessions influence the magnitude of the chronic change in ROM. Despite this variability in SS prescription, Medeiros and Martini (7) concluded that long-term SS results in approximately a 5° increase in dorsiflexion ROM in a recent meta-analysis.
Another method for increasing ROM that has been used in clinical settings and has recently gained popularity with the general population is the use of foam rolling (FR). This method requires the participant to use the bodyweight to create pressure between the foam roller and the muscle group(s) being foam rolled. Using a back and forth motion, the foam roller is rolled over the length of the muscle in an effort to improve ROM. Several studies have documented acute increases in ROM (23–26). The magnitude of this acute response varies based on the muscle group and surrounding tissues being foam rolled (27). García-Gutiérrez et al. (28) demonstrated a 6% increase in dorsiflexion ROM after three sets of 20 s of FR were completed. Similarly, Halperin et al. (29) demonstrated ~4% increase in dorsiflexion ROM after three sets of 30 s of roller massage. Conversely, de Souza et al. (27) reported ~11% increase in dorsiflexion ROM when participants completed two sets of 10 repetitions and 20 repetitions of FR. Therefore, the acute increase in dorsiflexion ROM also seems to be dependent on the FR stimulus.
There is conflicting and limited research on the long-term effects of FR on ROM. Junker and Stöggl (30) reported a 3-cm increase in the stand-and-reach test after 4 wk of FR the hamstrings. Participants performed three sets of 10 rolls during each session with three sessions performed each week. Hodgson et al. (31) reported no long-term change in hamstring or quadriceps ROM after 4 wk of roller massage training three times per week or six times per week. Hamstring flexibility was assessed by performing active and passive hip flexion while in the supine position with the knee in full extension. Quadriceps ROM was assessed using a kneeling lunge position. For each session, participants performed four sets of 30 s of roller massage. Aune et al. (32) reported no long-term change in dorsiflexion ROM in soccer players that performed three sets of 60 s of FR daily for 4 wk. The differing results in these studies may be attributed to differences in ROM assessment, pressure exerted by the modality used (foam roller or roller massage), and/or muscle groups rolled.
The research evaluating the synergistic effect of FR and SS on ROM is sparse and conflicting. Škarabot et al. (33) demonstrated a 9.1% acute increase in dorsiflexion ROM when adolescent trained swimmers with FR experience performed FR followed immediately by SS. This acute increase was significantly greater than the 6.2% increase due to SS alone. Interestingly, FR alone had no acute increase in ROM. However, Hodgson et al. (34) reported no acute synergistic effect for hip flexion and knee flexion ROM when recreationally trained subjects performed 30 s of SS followed by 30 s of roller massage. The long-term effects of FR alone or combined with SS have not been thoroughly evaluated. Mohr et al. (35) reported a 23.55° increase in hip flexion ROM compared with baseline after six sessions of FR and SS in hamstring flexibility in patients with limited flexibility. However, this change in ROM was determined by comparing the baseline assessment to the postintervention assessment at the end of the six sessions. Therefore, it is difficult to separate an acute response from a long-term response to FR and SS (36). Therefore, the purpose of the current study was to investigate the acute and long-term effects of 6 wk of SS and FR, separately and combined, on dorsiflexion ROM. We hypothesized that there would be differences in the acute response to SS, FR, and FR followed by SS in terms of dorsiflexion ROM before and after 6 wk of training with the acute response after training to be different than pretraining for all three groups. We also hypothesized that ROM would be improved for SS and FR followed by SS after 6 wk. We did not anticipate any long-term change in ROM for FR alone.
Forty-four healthy, university-age participants (n = 18 female (mean ± SD): age, 21.3 ± 2.0 yr; height, 162.7 ± 5.6 cm; mass, 70.4 ± 20.6 kg); n = 26 male (mean ± SD): age, 21.7 ± 1.7 yr; height, 176.0 ± 5.9 cm; body mass, 82.7 ± 11.9 kg)) were assigned to one of three groups (SS (n = 17), FR (n = 16), or the combination of FR and SS (FR + SS; n = 11)) using an online algorithm (www.randomization.com). At the beginning of the study, all participants completed the written informed consent form and health history questionnaire before having their dorsiflexion ROM assessed. All participants reported that they had not performed any lower extremity stretching, therapeutic massage, or FR within the month before participation. They were also instructed to refrain from stretching, FR, and therapeutic massage outside the study during their participation. The participants stretched and/or foam rolled both lower legs; however, only the dorsiflexion ROM from each subject’s dominant leg (kicking leg) was assessed to standardize the procedure. Each participant had their ROM assessed at the same approximate time of day throughout the study. Participants came to the laboratory twice per week for 6 wk to undergo the appropriate experimental treatment. We chose two sessions per week to minimize scheduling conflicts and ensure appropriate supervision of each session in the laboratory rather than allowing sessions to be completed outside the laboratory. Sessions were separated by at least 48 h. If they missed a session, they were required to come to the laboratory for three sessions during the following week, with the first session of that week counting as the second session of the previous week. Thus, 12 experimental sessions were completed in 6 wk for all participants. During week 7, dorsiflexion ROM was assessed a final time without any intervention. To ensure compliance and proper technique, all sessions were supervised by a member of the research team. All procedures were approved by the university’s institutional review board (Protocol No. 2017.15).
Ankle dorsiflexion ROM assessment
Each participant performed a wall stretch to assess dorsiflexion ROM in their dominant leg. Foot position was standardized for all measurements and stretches. With their dominant foot perpendicular to the wall, the subjects placed their weight on the outside edge of the sole of their foot to keep the talus in a neutral position, which should maintain the arch (37). Then, they pressed their first toe to the ground and held this position as they lunged forward with their nondominant foot while the knee of the dominant leg was in full extension, placing their hands on the wall for balance. The end point of their ROM was defined as the maximum point of discomfort without reaching their pain threshold. Once maximum dorsiflexion was achieved, a digital torpedo level (Model 320.48295; Craftsman) with an accuracy of ±0.1° was placed on the anterior shaft of the tibia with the most superior edge of the level immediately inferior to the tibial tuberosity. Two of the authors measured ROM for all participants. To avoid variability across raters, the same author tested the same participants throughout the study. These authors were blinded as to which group participants belonged. Three trials were performed during each assessment, with the trial producing the greatest dorsiflexion ROM being recorded for statistical analysis. Figure 1 shows the timeline for ROM assessments as well as when experimental treatments were conducted. Although we measured ROM during one session each week, only ROM data from the first session of week 1, the second session of week 3, the last session in week 6, and week 7 were used for statistical analysis.
Participants in the SS group performed the wall stretch as previously described for both legs. Each stretch was held for 30 s. One set was performed on the nondominant leg followed by one set performed on the dominant leg. A total of three sets of 30 s were completed for each leg based on Škarabot et al. (33).
Participants in the FR group used a foam roller on the posterior aspect of their lower legs using a high-density ethylene vinyl acetate foam roller (36 inches long, 6 inches in diameter; yogaaccessories.com). A member of the research team demonstrated the appropriate technique. With the nondominant lower leg laying on the foam roller, the participants used both hands and the dominant foot on the floor to support their weight (Fig. 2). A metronome set to 60 bpm was used to control the speed of FR. Participants used their arms and non–foam-rolled leg to propel themselves forward and backward to roll muscle belly of the triceps surae over the foam roller. They instructed not to foam roll down the Achilles tendon. With each beep of the metronome, participants either foam rolled up the lower leg or down the lower leg. Participants were instructed to foam roll over the muscle belly and avoid the popliteal fossa and gastrocnemius’ tendon origins. After 30 s of FR, the participant switched leg positions and foam rolled the dominant lower leg. A total of three sets of 30 s of FR was performed on both legs.
FR + SS group
Participants in the FR + SS group performed FR in the same manner as the FR group followed immediately by SS performed in the same manner as the SS group.
Based on previous work (30), a power analysis determined that at least nine subjects were needed per group based on an α of 0.05 and a power of 0.80. Specific comparisons were planned a priori. A one-way ANOVA was used to assess differences in ROM across groups in the initial baseline pretest measure. To assess differences in the acute response to training, ROM scores from the first day of training (pretest and posttest) were compared with ROM scores on the last day of training from week 6 (pretest and posttest) across groups using a 3 × 4 (group–time) repeated-measures ANOVA. Long-term changes in ROM were statistically analyzed using a 3 × 3 (group–time) repeated-measures ANOVA on the pretest ROM score from week 1 and ROM scores from weeks 3 and 7. When statistical significance was determined, post hoc tests using pairwise comparisons with a Bonferroni correction were used. The α level was set to 0.05. Results are reported as means ± SD.
There were no differences in pretest ROM scores from week 1 across groups (P = 0.308). Because of a significant Mauchly test for sphericity (P < 0.001), Greenhouse–Geisser correction was used when comparing the acute ROM response from week 1 to the acute ROM response from week 6. The results of the 3 × 4 repeated-measures ANOVA test for the acute response to training reported no significant interaction across groups. However, there was a significant main effect for time (F = 8.992, P = 0.001, ηp2 = 0.180, 1 − β = 0.934). Results of the pairwise comparisons showed that there was no difference before and immediately after the first day of training for any of the groups. During week 6, all three groups demonstrated an acute increase in ROM (P = 0.004). With all three groups combined, ROM increased by 4.0% during the last day of training in week 6. Although not significantly different from each other, the percent change in ROM during the last session in week 6 was 4.7%, 3.2%, and 4.3% for the SS, FR, and FR + SS groups, respectively.
Because of a significant Mauchly test for sphericity (P < 0.001), Greenhouse–Geisser correction was used when comparing the dorsiflexion ROM across week 1 pretest, week 3, and week 7. The 3 × 3 repeated-measures ANOVA that assessed longitudinal changes in ROM across groups demonstrated no significant interaction (P = 0.314). However, there was a main effect for time (F = 8.661, P = 0.002, ηp2 = 0.174, 1 − β = 0.887). For all three groups, ROM was not significantly different from week 1 to week 3 (P = 0.287), but increased from week 3 to week 7 by 8.4% (P < 0.001). Although not significantly different from each other, ROM increased from week 3 to week 7 by 10.6%, 5.6%, and 9.0% for SS, FR, and FR + SS, respectively. From week 1 to week 7, ROM for all three groups increased by 18.3% (P = 0.003). Although not significantly different from each other, ROM increased from week 1 to week 7 by 15.0%, 25.1%, and 13.5% for SS, FR, and FR + SS, respectively. Table 1 shows the dorsiflexion ROM for each group across time.
The purpose of this investigation was to compare the acute and long-term changes in dorsiflexion ROM for SS, FR, and FR + SS. Participants developed an acute increase in ROM over time for all three groups. In addition, ROM improved for all three groups over the duration of the entire study. Statistically significant changes in ROM occurred during the latter half of the study. The combination of FR and SS did not provide a synergist effect on increasing ROM acutely or over 6 wk of training. To our knowledge, this is the first study evaluating the effect of several weeks of FR + SS on ROM.
The SS results of our study are in partial agreement with previous studies. Although we did not have an initial acute response to SS during the first day of training, we did see a 4.7% acute increase in dorsiflexion ROM during the last day of training. Konrad et al. (12) also reported an acute increase of 4.3% in dorsiflexion ROM after police cadets completed four sets of 30 s of SS. Kay et al. (37) reported an acute increase of 5.2% in dorsiflexion ROM after three sets of 20 s of SS for recreationally active individuals, although this acute response was not different from the change in ROM when performing isometric contractions. Škarabot et al. (33) reported an acute increase of 6.2% in dorsiflexion ROM after three sets of 30 s of SS in resistance-trained, adolescent swimmers. In the previously mentioned studies, no attempt was made to standardize the position of the talus during stretching or during ROM assessment. In the current investigation, we attempted to place the talus in a neutral position by having the participants maintain the arch while stretching and while having their ROM assessed. Previous research has shown that subtalar joint position can influence dorsiflexion ROM (38). Unfamiliarity with this novel foot position in the current study may have increased antagonistic activity, thereby restricting the participants’ dorsiflexion ROM during week 1. Future studies may want to investigate different methods for standardizing foot placement that are less novel or attempt to implement a familiarization session that does not affect ROM.
In regard to long-term SS regimes, Medeiros and Martini (7) concluded in a recent systematic review and meta-analysis that dorsiflexion ROM can be improved by 5.17° using SS, regardless of dosage. Our long-term SS changes in ROM (4.8° increase) were in agreement with their conclusions. Blazevich et al. (39) demonstrated a 19.9% increase in dorsiflexion ROM after four sets of 30 s of SS, which was performed twice daily over 3 wk. Konrad and Tilp (21) reported a 17.5% increase in dorsiflexion ROM after four sets of 30 s of SS performed for five sessions per week for 6 wk. Hayes et al. (22) reported a 42.25% increase in dorsiflexion ROM after 6 wk of SS, which was performed five sessions per week with each session containing five sets of 30 s of stretching. In the current study, the 4.8° increase in ROM due to SS resulted in a 12.6% increase in ROM after three sets of 30 s of SS, which was performed twice per week for 6 wk. Differences in the magnitude of percent change between the current study and previous studies may be attributed to differences in SS dosage and number of stretching sessions completed.
Acute increases in ROM due to SS have been attributed to an increased stretch tolerance (6,40) and/or an increased compliance of the musculotendinous unit (6,19). Whatman et al. (41) documented acute changes in passive stiffness after four sets of 20 s of hamstring stretching. Although musculotendinous unit compliance remained increased for at least 20 min after treatment, they reported that the only clinically meaningful posttest assessment of passive stiffness was immediately after treatment. Interestingly, Konrad and Tilp (21) reported no changes in muscle stiffness, tendon stiffness, fascicle length, or pennation angle after 6 wk of plantar flexor SS. They concluded that these long-term changes in ROM due to SS were attributed to an increased stretch tolerance possibly due to adaptations to nociceptive endings (21). Previous research has suggested that the increased ROM in healthy individuals due to SS training protocols lasting no more than 8 wk seems to be caused by an increased stretch tolerance (42,43). Therefore, the longitudinal changes in ROM due to SS in the current investigation may be due to an increased stretch tolerance.
In the current investigation, there was no acute change in dorsiflexion ROM due to FR on the first day of training. Škarabot et al. (33) also evaluated the acute effect of SS, FR, and FR + SS using the same dosage of FR (three sets of 30 s) as the current investigation. Although they did not control the speed of FR, their FR alone results were similar to ours in that there was a nonsignificant 2.8% acute increase in dorsiflexion ROM. However, the acute response during the last training session for the current study demonstrated a 3.2% increase in dorsiflexion ROM for the FR group. Our results are also similar to Halperin et al. (29), who documented a 3.6% increase in dorsiflexion ROM 1 min after subjects completed three sets of 30 s of roller massage at a rate of one roll in 1 s, which is the same as our FR protocol. Although no study to date has compared them directly, this suggests that FR and roller massage produce similar results. Aune et al. (32) demonstrated a 9% increase in dorsiflexion ROM 30 min after participants completed three sets of 60 s of FR. This suggests that a dose–response relationship exists between FR and the magnitude of the acute increase in ROM.
In the current study, we reported a 25.1% increase in dorsiflexion ROM using FR after 6 wk of training. Although this percent increase is not statistically different from the improvements in ROM induced by SS alone or FR + SS, this study is one of the very first investigations into long-term changes in ROM induced by FR. Aune et al. (32) reported a 7% improvement in dorsiflexion ROM when participants performed three sets of 30 s of FR daily for 4 wk, which was not different from the increase in ROM induced by eccentric training. However, the FR speed was not standardized among participants. Hodgson et al. (31) also reported no improvement in hamstring ROM after 4 wk of FR using four sets of 30 s of roller massage performed either three times per week or six times per week with the same cadence as the current investigation. However, they had seven to eight subjects in each group. Junker and Stöggl (30) reported 3- or 4-cm increases in hamstring flexibility as measured by the stand-and-reach test after participants completed 4 wk of FR or proprioceptive neuromuscular facilitation training, respectively. Their FR protocol consisted of three sets of 10 rolls back and forth over the hamstrings. The differing results between these previous studies and our current study may be attributed to differences in FR speed and duration as well as sample size. Furthermore, hamstring flexibility may be due to limitations in neural tension rather than any myofascial component (44).
Research studies evaluating FR on the contralateral limb have documented acute increases in ROM (28,45), suggesting some neural involvement as a potential mechanism. In addition, changes in pain pressure threshold have been documented immediately after FR (46–48) or roller massage for the rolled muscle groups (47–49) as well as the contralateral muscle groups. This suggests that FR’s mechanism for an acute increase in ROM is likely due to an increased stretch tolerance with some neural involvement. Another possible mechanism is an increased blood flow to the area, thereby producing a warm-up effect. Okamoto et al. (50) documented significant increases in nitric oxide concentration after participants performed 20 repetitions of FR over the adductors, hamstrings, quadriceps, iliotibial band, and trapezius. Hotfiel et al. (51) demonstrated an increased blood flow to the lateral thigh after three sets of 45 s of FR. In theory, this could increase local temperature in the surrounding tissues to improve ROM and warrants future study. Long-term changes in ROM due to FR may also be attributed to an increased stretch tolerance and/or increased blood flow. Future studies may wish to evaluate these potential mechanisms.
FR + SS
To date, there are only two studies evaluating the synergistic effect of FR + SS, excluding the current investigation, and one study evaluated the synergistic effect of SS combined with roller massage. One study demonstrated a 9.1% acute increase in ankle ROM when adolescent swimmers who have been using FR performed FR + SS when using the Grid Foam Roller, which seemed to apply more pressure than traditional foam rollers (33). Participants placed the contralateral leg on the foam-rolled leg to increase the pressure exerted by the foam roller. This led to an increase in ROM that was statistically different from the 6.2% acute increase due to SS alone. Methodological differences between this study and the current investigation include differences in previous FR experience, pressure exerted by foam roller, differences in assessing ROM, and differences in potential experimenter bias. Škarabot et al. (33) used subjects who were currently FR for the previous 6 months. We only recruited participants who had not participated in FR for the previous month. This could lead to differences in the amount of pressure each participant is able to exert on the foam roller without inducing pain. Although previous studies have documented no difference in the increase in ROM when varying the pressure exerted by a foam roller (52) or roller massage (53) alone, we cannot rule out the possibility of a synergistic effect on ROM for different pressures exerted combined with SS. The differences in pressure used in these studies and the present investigation combined with SS may explain the differing results. Future studies may wish to explore the optimal combination of pressure exerted by the foam roller or roller massage and SS dosage to enhance ROM. Škarabot et al. (33) assessed ROM by using a weight-bearing lunge test with the knee flexed. In the present study, a wall stretch was used where the knee was placed in full extension. This difference in knee joint position could shift the restriction of ROM from the gastrocnemius during the wall stretch to the soleus during the lunge test. Because of the lack of research in this area, it is unclear if differences in FR + SS in terms of ROM were due to differences in knee position. Škarabot et al. (33) were not blinded as to which treatment the subjects were receiving when assessing ROM. In the current investigation, the two judges that were determining ROM were blinded as to which group each participant was receiving.
Hodgson et al. (34) also documented an acute synergistic effect for improving hip and knee ROM when performing a single 30-s bout of SS followed by a single 30-s bout of roller massage. This suggests that the hamstrings and quadriceps may be respond more robustly to FR or roller massage combined with SS than the triceps surae. Mohr et al. (35) also showed a synergistic effect of FR + SS in subjects with limited hamstring flexibility after six training sessions. However, because of the nature of the experimental design, it is impossible to separate the acute response from any long-term changes that may have taken place (36). The current study was designed to apply our results to the general population, separating acute and long-term responses to FR + SS. Our findings showed that there was no synergistic effect of FR + SS on dorsiflexion ROM for the general population after 6 wk (12 sessions) of training. Longer training studies, studies using a greater training dosage and/or frequency, and studies evaluating muscles/joints that have a larger ROM may show a different response to FR + SS.
In the present study, there was no synergistic effect of FR + SS on dorsiflexion ROM for the young, healthy adult population. FR and SS were equally effective at acutely increasing ROM after training and equally effective at increasing ROM after 6 wk (12 sessions) of training. Different dosages of FR, SS, and FR + SS may produce different results. Furthermore, clinical populations may experience different results.
The authors of this study have no conflicts of interest to declare. The results of the present study do not constitute endorsement by the American College of Sports Medicine. The results of the present study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation. No funding was received for this investigation.
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