Effects of therapeutic and aerobic exercise programs in temporomandibular disorder-associated headaches

Abstract Objective To assess the effects of three 8-week exercise programs on the frequency, intensity, and impact of headaches in patients with headache attributed to temporomandibular disorder (TMD). Methodology Thirty-six patients diagnosed with headache attributed to TMD participated in the study and were divided into three groups of 12 patients: a therapeutic exercise program (G1, mean age: 26.3±5.6 years), a therapeutic and aerobic exercise program (G2, mean age: 26.0±4.6 years), and an aerobic exercise program (G3, 25.8±2.94 years). Headache frequency and intensity were evaluated using a headache diary, and the adverse headache impact was evaluated using the Headache Impact Test (HIT-6). The intensity was reported using the numerical pain rating scale. These parameters were evaluated twice at baseline (A01/A02), at the end of the 8-week intervention period (A1), and 8–12 weeks after the end of the intervention (A2). Results At A1, none of the G2 patients reported having headaches, in G1, only two patients reported headaches, and in G3, ten patients reported headache. The headache intensity scores (0.3 [95% CI: -0.401, 1.068]), (0.0 [95% CI: -0.734, 0.734]) and HIT-6 (50.7 [95% CI: 38.008, 63.459]), (49.5 [95% CI: 36.808, 62.259]), significantly decreased in G1 and G2 at A1. At A2 headache intensity scores (0.5 [95% CI: -0.256, 1.256]), (0.0 [95% CI: -0.756, 0.756]) and HIT-6 (55.1 [95% CI: 42.998, 67.268]), (51.7 [95% CI: 39.532, 63.802]) in G1 and G2 haven’t change significantly. The effects obtained immediately after the completion of the intervention programs were maintained until the final follow-up in all groups. Conclusion The programs conducted by G1 (therapeutic exercises) and G2 (therapeutic and aerobic exercise) had significant results at A1 and A2.


Introduction
Headaches and temporomandibular disorders (TMDs) frequently occur simultaneously, 1 and associated to each other. 2,3 Both are comorbid conditions, that is, the presence of one increases the frequency of the other 4 ; for example, the more TMD symptoms a person experiences, the more frequent their headaches are, and vice versa. 5 Due to the biomechanical aspects of TMD and the headaches, there is a constant interaction between these diseases, since TMD may lead to the development of headaches, due to the pain in the masticatory muscles. This disorder can also become a predisposing and aggravating factor for the onset of headaches. 6 The overlap between TMD symptoms and headaches hinders the process of diagnosis and treatment. Moreover, the high level of association between the diagnostic criteria and the peripheral and central nervous structures involved in the two disorders further complicates the process. 1,7 Physiotherapy is the most frequently used alternative or complementary headache intervention strategy. 8 Therapeutic exercises are the most common interventions, 9 including joint mobilization, therapeutic massage and other body-based therapies; however, evidence supporting the effectiveness of these interventions is still scarce. 10,11 Therefore, further investigations should evaluate the effects of physical therapy individually as a part of a multimodal approach, 11 since studies present multiple types of interventions, hindering results comparisons. 10,12 Aerobic exercise seems to be effective in decreasing the intensity and frequency of headaches, but the heterogeneity of study protocols does not allow us to determine the intensity of aerobic exercise needed and the most appropriate modality to reduce symptoms; therefore, an exercise prescription cannot often be formulated. 13 To date, evidence on the combined effect of therapeutic and aerobic exercise are scarce. The null hypothesis is that patients with headache attributed to TMD undergoing a combined program of therapeutic exercises with aerobic exercises (G2) will not show a with the Helsinki Declaration and understood that they were free to withdraw from the study at any time.
The null hypothesis is "patients with headache attributed to TMD undergoing a combined program of therapeutic exercises with aerobic exercises (G2) will not significantly reduce the frequency, intensity and adverse impact of headaches". The hypothesis one is "patients with headache attributed to TMD undergoing a combined program of therapeutic exercises with aerobic exercises (G2) will significantly reduce the frequency, intensity and adverse impact of headache".
Patients were distributed in three exercise groups. G1 to who did not agree to perform aerobic exercise, and G2 and G3, randomly, to the remaining patients. Patients in the G2 group participated in a weekly physiotherapy session, the same described for G1, for 8 weeks. The G2 aerobic exercise program included two weekly cycle ergometer training sessions, which were always supervised by the same physiotherapist and lasted for 30 min. Patients cycled for the first 5 min (warm-up period) with an intensity of 50% of the heart rate reserve (HRR), the next 24 minutes with an intensity of 70% of HRR, and the last minute at 50% of HRR for active recovery. The speed and/or resistance of the cycle ergometer was adjusted throughout the training period to maintain the exercise intensity within a predefined value. HRR was determined according to the Karvonen formula 18 and the resting heart rate (HR) was assessed on 3 consecutive days after 5 min of rest in a chair with the arms supported. The average value was calculated and used as the resting HR.
Patients in G3 underwent 2 cycle ergometer training sessions per week for 8 weeks, which were always supervised by the same physiotherapist and lasted 30 min. The protocol was the same as that defined for G2.
Headache frequency/intensity were assessed through entries to a headache diary during the period between the first and the last evaluation. Patients were directed to record all episodes of headache experienced weekly and determine the intensity of the headache using the numeric pain rating scale (NPRS) of 11 items. The time elapsed since the first episode of headache was assessed through the DC-TMD symptom questionnaire, and the mapping through self-reported Headache Impact Test (HIT-6) questionnaire. 19 Patients who had headache attributed to TMD at the end of the intervention period were referred to a multidisciplinary medical team specializing in headache.

Statistical analysis
Categorical variables were analyzed using Pearson's chi-square test to confirm equality between groups at A01. Whereas for continuous variables, a nonparametric Kruskal-Wallis test was performed to confirm equality between groups at A01. A two-way mixed ANOVA was used to assess the differences between variables at the various assessment times (random factor) and for the 3 intervention groups (fixed factor). A 95% confidence interval (CI) was determined for all tests, and a 5% significance level was used. The SPSS® version 26 (IBM Corp., Armonk, NY) was used for all statistical analyses. Cohen's d effect size was also calculated; effect sizes up to 0.2 were considered irrelevant, those between 0.2 and 0.5 were considered small, those between 0.5 and 0.8 were considered moderate, and values above 0.8 were considered large.

Results
The sample consisted of 52 patients; however, we excluded those without headaches attributed to TMD at the beginning of the study and studied the evolution between groups. We were left with 36 patients, 12 per group, still with no differences between groups at A0 (χ2=1.83, p=0.4). Each group was composed of 10 women and 2 men ranging from 18 to 35 years of age.

Headache impact test
Analysis of the three groups at A01 and A02 verified that the HIT-6 was not significantly different (H=0.25, p=0.78). Changes in HIT-6 after the intervention programs (A1) were favorable for patients in G1 and G2, being significantly different from G3. Between A1 and A2, there was a slight increase in HIT-6, but it was not significant, nor did it have a notable effect size (Table 1)  Headaches and TMD are comorbid conditions, that is, they occur frequently in the same individual. 1,2,7,14,[20][21][22] Regarding the time elapsed since the onset of symptoms, only 2 patients (16.7%) from G1 and G2 reported the presence of pain for less than 6 months, whereas only one in each group reported the presence of a headache for less than 3 months. According to the definition of chronic pain, 23,24 this seems to indicate that most patients had a chronic headache if defined as lasting a period of 3 months from the first episode. Chronic pain is maintained in part by central sensitization, a phenomenon seems to be associated by prolonged, long-lasting nociceptive stimulation or by decreased pain inhibition. Changes in these circuits may change perception of pain independent of peripheral neural activation in patients. 25 The fact that most of patients that participated in the study reported headache attributed to TMD for more than 6 months may indicate that they have central sensitization.
The number of headache attributed to TMD episodes reported after the intervention programs decreased in all groups, and in G2, none of the patients reported headaches at A1. In G1, only two patients (16.7%) reported a headache, with a maximum  Subtitle: G1 -experimental group that carried out a therapeutic exercise program; G2 -experimental group that associated a therapeutic exercise program with aerobic exercise; G3 -experimental group that carried out a therapeutic exercise program; A01-evaluation baseline one; A02 -evaluation baseline two; A1 -evaluation post-intervention three; A2 -follow-up; HIT-6 -Headache Impact Test (36-78 points). frequency of 2 episodes per week, and in G3, only 2 patients (16.7%) reported having no headaches. After the intervention in G2, G1, and G3, the intensity of headaches attributed to TMD significantly decreased, despite the greater difference in the first two groups compared to the third, also in G2 all patients stopped reporting pain. The results obtained in G1 are in line with those observed by et al. 26 (2015) which a decrease in the frequency and intensity of headaches was identified after performing a therapeutic exercise protocol. However, in the same study, a manual therapy program was compared with a pharmacological approach, which makes the comparison of results more difficult. 26 The programs with identified therapeutic exercises are quite heterogeneous but have been shown to be effective in reducing pain in various health conditions. [27][28][29] However, the results obtained in our study seem to indicate that the therapeutic exercise program developed for the masticatory muscles (type and sequence of exercises, number of repetitions, weekly frequency and time period of eight weeks) led to a significant reduction in the intensity and frequency of headaches attributed to TMD and a retention of these effects in the short / medium term.
In G3, the results were also in line with the literature. A systematic review conducted by et al. 13 (2020) observed that aerobic exercise was effective in reducing the intensity of headaches by 75%, a higher value than that obtained in our study, in which the reduction was approximately 50%. In the systematic review, the 25% reduction of frequency was effective, and the same value that was found in our study. In contrast, Lemmens,et al. 30 (2019)  The adverse impact of headaches on patient lives is multidimensional. 32 Therefore, it is important to analyze effects on different aspects of daily living.
The results of HIT-6 showed a decrease in G1 and G2 scores after completion of the intervention programs.
The minimum clinically important difference defined for HIT-6 was between 2.5 and 5.5 for migraines 33 and 8 points for tension-type headache (TTH), 34 with no studies identified for headaches attributed to TMD. Compared to previous studies, the present G1/ Regarding impact, any of the groups still had the same results as those that were observed after the end of the intervention programs, therefore, it is possible to say that overall, the positive effects were maintained. This study has some limitations, such as the small, convenience-based sample, which means that the findings may not be generalizable to other populations. The sample also included only subjects aged between 18 and 35 years, which does not allow the extrapolation of results to other age groups.
The non-acceptance rate by several patients to join

Conclusion
The greatest effects on decreasing headache attributed to TMD frequency and intensity were observed in the group whose intervention program consisted of therapeutic and aerobic exercises (G2), in which none of the patients reported headaches attributed to TMD at A1. Although the differences were not significant considering the group with the therapeutic exercise program (G1), in which only two patients reported having a headache attributed to TMD. There were no significant differences in followup (A2) compared to A1. In conclusion, programs that associated therapeutic with aerobic exercises had positive effects in patients with headache attributed to TMD after an eight-week intervention period and at the end of interventions, meaning that these programs maintained a positive effect in the short/medium term.

Conflicts of interest
The authors declare no conflict of interest.