Variação da pressão intraocular no exercício resistido realizado em duas diferentes posições Variation of intraocular pressure in resistance exercise performed in two different positions

Variação da pressão intraocular no exercício resistido realizado em duas diferentes posições Variation of intraocular pressure in resistance exercise performed in two different positions Alex Sander Soares1, André Athanazio Caldara1, Lucas Ruiz Storti1, Luis Felipe Milano Teixeira1, João Guilherme Torniziello Terzariol1, Marcelo Conte1 1 BOS Fit, Núcleo de Estudos e Pesquisas em Ciências do Esporte, Hospital Oftalmológico de Sorocaba (SP), Brasil. Os autores declaram não haver conflitos de interesse Recebido para publicação em 22/01/2013 Aceito para publicação em 29/09/2013 Objetivo: Verificar a variação da PIO no exercício resistido na posição sentada e em decúbito dorsal. Métodos: Foram avaliados 14 voluntários do Centro de Atividades Físicas do Banco de Olhos de Sorocaba (BOS Fit). Os critérios de exclusão adotados foram: I) opacidade de meios; II) alteração de volume do bulbo ocular ou ausência de bulbo ocular; III) PIO maior do que 21mmHg; IV) idade inferior 20 e superior a 40 anos; V) tempo de prática de treinamento resistido inferior a 30 dias. Inicialmente foi realizado o teste de predição no exercício leg press para determinar o percentual de carga para o respectivo exercício durante o experimento. Os voluntários foram submetidos a duas intervenções separadas em um intervalo de 72 horas, ambas com o mesmo volume e intensidade no exercício leg press, ou seja, 3 séries de 15 repetições com 60% 1RM, tempo de intervalo entre as séries de 60 segundos e velocidade moderada, de acordo com as seguintes posições: P1) leg-press executado na posição sentada e P2) leg press na posição em decúbito dorsal. A PIO foi obtida utilizando o tonômetro de Perkins em três momentos: M1) imediatamente antes do exercício; M2) imediatamente após a terceira série; M3) três minutos após a finalização da terceira série. Resultados: Em ambas as posições houve queda significativa da PIO após o exercício (M2), permanecendo significativamente reduzida após três minutos de recuperação (M3). Contudo, não houve diferença da PIO segundo a posição (P1 e P2), independentemente do momento de aferição (M1, M2 e M3). Conclusão: Houve queda da PIO decorrente ao exercício resistido e não foi verificada resposta diferencial da PIO de acordo com a posição do exercício. Descritores: Pressão intraocular/fisiologia; Exercício; Treinamento de resistência; Postura Objective: To verify the variation in IOP in the resistance exercise performed in the sitting and supine. Methods: A 14 volunteers of the Center for Physical Activities of the Sorocaba Eye Bank (BOS Fit). Exclusion criteria were adopted: I) media opacity; II) change in volume of the eyeball or no eyeball; III) IOP greater than 21mmHg; IV) age 20 and over 40; V) time practice of resistance training less than 30 days. Initially the test was performed to predict the leg press exercise to determine the percentage charge for the exercise thereof during the experiment. The volunteers underwent two interventions separated by an interval of 72 hours, both with the same volume and intensity in the leg press exercise, 3 sets of 15 repetitions with 60% 1RM, interval time between sets 60 seconds and moderate speed, according to the following positions: P1) leg press performed in the sitting position and P2) leg press in supine position. IOP was obtained using the Perkins tonometer in three moments: M1) immediately before exercise; M2) immediately after the third series; M3) three minutes after completion of third grade. Each sequence was obtained by measuring the position of their exercise performance. Results: We found that in both positions there was a significant drop in IOP after exercise (M2), remained significantly reduced after three minutes of recovery (M3). However, there was no difference in IOP second position (P1 and P2), regardless of time of measurement (M1, M2 and M3). Conclusion: There was a decrease in IOP due to resistance exercise and was not observes differential response of IOP of IOP according to the position of the exercise.


INTRODUCTION
T he intraocular pressure (IOP) is determined by the production, circulation and drainage of aqueous humor through trabecular and uveoscleral outflow, and also by the episcleral venous pressure (1) .The vitreous volume, choroidal blood volume, scleral rigidity, orbicular muscle tension of the eye and the external pressure may also affect the IOP (2) .Besides that, the IOP can be varied due to several factors such as circadian rhythm (3) , body position (4) , physical exercise (5) , among others.
In relation to the circadian rhythm there is an IOP peak in the early morning hours and the value becomes lower in the late afternoon, with floating of 4 to 6 mmHg.Said variation is related to the activity of the autonomic nervous system, humoral control and change muscle tone (3,4,6,7) .However, it was found that regardless the body position there is a significant increase in the IOP at night that is kept until the early morning hours, but the daily curve of IOP shows differences according to age (8) .
As for the body position, the IOP lying down is higher than sitting, and possibly the hydrostatic changes such as the elevated episcleral venous pressure which occur from one position to another may explain said differences (9) .Regarding physical exercises, both aerobic and anaerobic activities -including weightlifting (resistance training) -show a reduction in the IOP due to the reduction of plasma osmolality, hyperventilation, increased nitric oxide synthesis, reduction in plasma pH, among other mechanisms (10,11) .
On the other hand, it is known that there is an IOP variation due to the change in body position, patients in supine position have higher blood pressure values in relation to the measurements obtained in the sitting position, and the increased episcleral venous pressure (12) may be considered as an important factor for IOP fluctuation resulting from the change in posture.
In fact, studies have demonstrated the hypotensive effect of resistance training in IOP.However, it is not defined in the literature if exercises performed in different positions also have different effects on IOP.
In this sense the objective of the present study was to verify the IOP variation in the resistance training in the sitting position and in the supine position.

Sample
This experimental study was conducted in healthy patients submitted to two resistance training sessions.By convenience the sample consisted of 20 patients (10 male and 10 female).The exclusion criteria adopted were: i) media opacity; ii) volume change of ocular bulb or absence of ocular bulb iii) age below 20 or over 40 years old, and iv) time practicing resistance training below 30 days.The inclusion criteria considered was a medical certificate corresponding to clinical and laboratory assessment and electrocardiogram.The experimental procedures were carried out on the premises of the Physical Activities Center of the Eye Bank if Sorocaba (BOS Fit).
The protocol was conducted following the ethical principles established in the Declaration of Helsinki proposed by the World Medical Association.The project was sent to approved by the Research Ethics Committee of the Ophthalmology Hospital of Sorocaba (opinion No.101.533).All participants were informed about the research and their respective degree of involvement, and then asked to sign the Informed Consent, consisting of explanation about the following aspects: i) justification, objectives and procedures used; ii) discomfort, possible risks and expected benefits; iii) form of follow-up and assistance and their guardians; iv) information on the possibility of inclusion in the control group; v) freedom to refuse to participate or withdraw their consent at any stage of the research, without penalty or loss and vi) guarantee of confidentiality in relation to the data collected.

Instruments and procedures
To determine the training loads, the prediction test (13) initially performed was the leg-press exercise, which aims to estimate the maximum load for resistance training by means of the application of submaximal loads to exhaustion.According to the relevant protocol, a random load is applied, and the volunteers as asked to exercise to fatigue.The repetitions are recorded and related to a specific table to check the estimated load to be used in the experiment, here 60% of one maximum repetition (1MR).
The volunteers underwent two interventions separated by an interval of 72 hours, both with the same volume and intensity in the leg-press exercise, i.e., 3 sets of 15 repetitions with 60% 1MR, a time interval between series of 60 seconds and moderate speed, according to the following positions: P1) leg-press performed in a sitting position and P2) leg-press in the supine position.The IOP was obtained using the Perkins tonometer, always by the same ophthalmologist with experience in this technique, in three moments: M1) immediately before the exercise, M2) immediately after the third set and M3) three minutes after the completion of the third set.Each measurement sequence was obtained in the respective performance position of the exercise, watching a distant object with the contralateral eye, after instillation of a droplet of proparacaine eyedrops and a droplet of fluorescein eyedrops.Although the Goldman applanation tonometer is considered the gold standard for the measurement of IOP, other tonometers shoe good mesurement correlation (14,15) .In this study, the use of the Perkins tonometer is justified by the practicality of employment in field situations of physical exercise, allowing it to be taken anywhere and that the measure is made with minimal displacement of the patient assessed, as well as allowing the measurement in the supine position (16) .

Statistical analysis
The mean and the standard deviation were descriptively calculated, and the data were presented in the tabular form and in box diagram (Box-plot).We used ANOVA with repeated measures and Bonferroni post-test, adopting a significance level of 5% to compare to the measures for the variables studied.The software used was GraphPadPrism ® .

RESULTS
Table 1 shows the IOP response in both positions at three different moments, and demonstrates the significance in reducing the IOP after the beginning of the exercise.
It was observed that in both positions there was a significant decrease in IOP after the exercise (M2), remaining significantly reduced after three minutes of recovery (M3).However, there was no difference in IOP according to the position (P1 and P2), regardless of the moment of measurement (M1, M2 and M3).
Figures 1 and 2 show the variation of IOP in the right eye (RE) and left eye (LE) according to the position in the moments pre-exercise (M1), post-exercise (M2) and three minutes after exercise (M3).

DISCUSSION
In a study of boxing athletes who underwent resistance training sessions, values significantly lower in the IOP were found Table 1 IOP response according to the position of the exercise and according to the assessment moment  after performing the exercises, regardless the body position of the volunteers (17) .
However, a survey was conducted with 82 patients not subject to physical exercise which presented the following conditions: primary open angle glaucoma (POAG), normal pressure glaucoma (NPG) and individuals with normal eyes (NE).It was observed that the IOP was higher in the supine position than in the sitting position (18) , regardless of the condition.The mean difference in IOP between the supine and the sitting positions in the POAG was 3.41mmHg.However, the NPG group was 2.77mmHg, and finally in volunteers with NE the difference found was 2.45mmHg.The authors consider that the respective difference may be associated with increased episcleral venous pressure.
It is also pointed out that the exercises performed with the legs positioned above the head can result in elevation of IOP (19) .On the other hand, this increase may be due to increased choroidal vasculature and episcleral venous pressure, in which the flow of ocular tissues becomes committed, and the choroid is a very vascularised tissue which can cause dynamic changes in the aqueous humor liquid, causing increased IOP (20) .
Another study (21) which also found that the variation in the aqueous humor drainage according to the body position found that the average IOP in 21 volunteers in the sitting and supine positions was significantly different, i.e., respectively, 17.8+1.7mmHgand 19.9+1.6mmHg.On the other hand, there was no significant difference in the aqueous humor drainage according to the body position, with observed values of 0.30+0.31(seatting) and 0.28+0.09l/min/mmHg(supine) Regarding the volume and intensity of training (17,22) it is observed that the resistance training causes a decreased IOP regardless of the load used during the exercise session, with a greater change in the method which calls for the development of muscle strength.In fact, in these conditions the total volume of training and the time in which the muscles remain under tension are higher than in other methods of resistance training.However, the supine exercise performed with maximum load for four repetitions in voluntary apnea caused a mean increased IOP of 4.3±4.2mmHg in young healthy volunteers (23) .
Hypothetically, exercises performed in the supine position would naturally increase the IOP levels.However, the hypotensive effects of resistance training (7,11,17,24) seems to interfere in this process, antagonizing the potential increase in IOP by mechanisms that promote the reduction of the formation and/or increased aqueous humor outflow.

Figure 1 .
Figure 1.Changes in the IOP in the RE according to the position, second moment.

Figure 2 .
Figure 2. Change in the IOP in the LE according to the position, second moment Soares AS, Caldara AA, Storti LR, Teixeira LFM, Terzariol JG T, Conte M