The potential of elastic bands to optimize ocular and cardiovascular responses, subjective effort, and performance in squats

  1. Gené Morales, Javier
Dirigida por:
  1. Mª Rosario Salvador Palmer Director/a
  2. Andrés Gené Sampedro Director
  3. Juan Carlos Colado Sánchez Director/a

Universidad de defensa: Universitat de València

Fecha de defensa: 07 de abril de 2022

Tribunal:
  1. Celia Sánchez-Ramos Roda Presidenta
  2. José Francisco Guzmán Luján Secretario/a
  3. Sandra Johanna Garzón Parra Vocal

Tipo: Tesis

Teseo: 716853 DIALNET

Resumen

Physical exercise and sports practice are common habits in most population groups. Physical exercise and more specifically resistance training have innumerable benefits for health and performance. To maximize these benefits, it is necessary to evaluate performance and physiological adaptations that can be achieved depending on the methodological features of the activity or exercise performed. As presented in Chapter 1, different training program variables (e.g., exercise selection, intensity, volume, effort level, and materials used) produce different responses. Therefore, the study of varied training methodologies is required. The squat is one of the most commonly selected exercises for resistance training routines due to its similarity to a wide range of athletic and everyday activities. Each different squat variation presents different biomechanical characteristics and entails different neuromuscular acute effects. Consequently, it is necessary to study the squat exercise and its different variations to deeply understand the movement and to individualize resistance training programs. Concerning materials, elastic bands are increasing in popularity for resistance training with both health and performance purposes. Elastic bands provide greater resistance (more kilograms) when they are longer and fewer kilograms when they are shortened. Accordingly, from a performance perspective, elastic bands can provide optimum resistance throughout the range of motion in squats. For squats, elastic bands are usually attached to the bar to provide the pertinent resistance measured at the participant’s standing position, as is done when using weight plates to load the bar. Therefore, the weight at the participant’s standing position is the same whether one uses elastic bands or weight plates. However, elastic bands provide less weight throughout the range of movement below this point. This makes the comparison between elastic bands and weight plates in terms of used resistance uneven. Within the range of motion of certain resistance training exercises such as the squat, there exists the so-called sticking region. The sticking region is defined as the part of the range of motion in which a disproportionally large increase in difficulty occurs, and this is considered a mechanical constraint. Bearing this in mind, the question arises whether elastic bands could be attached to the bar right above the sticking point (the point at which the sticking region ends) to provide the pertinent weight. This would make it possible to obtain less weight in the parts of the range of motion that are biomechanically disadvantageous and more weight in the biomechanically efficient parts of the exercise. Attaching the elastic bands to the bar immediately above the sticking point would therefore result in more weight during more degrees of movement and less weight during fewer degrees of movement compared to weight plates. Therefore, this way of applying the elastic bands could be a useful strategy to overcome the squat sticking point and enhance performance. This new methodology could allow participants to perform more repetitions with more weight compared with what they would be able to move with weight plates. To the best of our knowledge, no previous research has evaluated the effects of attaching the elastic bands to the bar immediately above the squat sticking point. The elastic bands would therefore be providing the pertinent weight at the sticking point instead of at the standing position of the participant. Focusing on health, resistance training has been shown to influence cardiovascular and ocular parameters both acutely and chronically. This influence on cardiovascular (e.g., systolic and diastolic blood pressure, mean arterial blood pressure, pulse pressure) and ocular parameters (e.g., intraocular pressure, ocular perfusion pressure) could vary depending on training program variables such as the weight used, the level of effort, or the materials used. These cardiovascular and ocular acute adaptations could be detrimental rather than beneficial for the development and progression of cardiovascular conditions associated with blood pressure such as hypertension, which is the leading modifiable risk factor for cardiovascular disease and premature death. Furthermore, dramatic increases or fluctuations of intraocular pressure and/or ocular perfusion pressure decreases could entail a risk for the development of ocular conditions such as primary open-angle glaucoma, which is the second most common cause of irreversible blindness worldwide. Responses of the cardiovascular system to physical exercise have been widely studied with relatively homogeneous results. On the other hand, there is controversy regarding the intraocular pressure behavior with certain physical exercise methodologies such as resistance training, including the squat. While several studies indicate that intraocular pressure increases and ocular perfusion pressure decreases with resistance training, other research has found the opposite. It is worth highlighting that in the deepest phases of the squat, the intraabdominal pressure rises, and this could lead to intracranial pressure and intraocular pressure elevation. Therefore, considering that elastic bands modify the kilograms provided throughout the range of motion, the question arises whether the use of elastic bands to load the bar in squats may provoke different cardiovascular and/or ocular acute adaptations compared to traditional resistance training devices (in particular, weight plates). Furthermore, numerous studies have shown that sex, age, central corneal thickness, and baseline levels of intraocular pressure, inter alia, could be correlated with intraocular pressure levels and fluctuations. In consequence, it is crucial to understand the moderating role that sociodemographic and physiological variables can play in individual variations of intraocular pressure with exercise. We did not find previous studies analyzing the prediction potential of sex, age, baseline levels of intraocular pressure, and baseline levels of central corneal thickness in the variations of intraocular pressure caused by exercise. Aims Bearing in mind what has been mentioned in the introduction, the compendium composing the present doctoral thesis was aimed at assessing the potential use of elastic bands to load the bar in squats and its relationship with ocular and cardiovascular health parameters, subjective effort, and performance. Additionally, two preliminary studies were designed to identify potential predictors of the intraocular pressure variations after exercise and to select the most appropriate squat variation for the present project, respectively. The study design, main results, and conclusions of each of the four articles included in the compendium, which justify the original contribution of the present doctoral thesis, are presented below. First study: The potential of sex, age, and baseline intraocular pressure to predict intraocular pressure variations with exercise The first article of the compendium is included in Chapter 2. It was aimed at identifying mediator parameters in the intraocular pressure changes after exercise. For this purpose, a multiple linear regression was conducted with age, sex, baseline intraocular pressure levels, and baseline central corneal thickness levels as potential predictors of intraocular pressure variations after a 90-minute acrobatic gymnastics session. Forty-nine healthy gymnasts with at least six months of experience (63.27% females, age: 27.67 ± 7.10 years, range: 18–40 years) voluntarily agreed to participate in the study. Two sessions were conducted. One session was used for familiarization and to confirm the suitability of the participants for the study according to the inclusion criteria. The second session was conducted to complete the research procedures. In this experimental session, measurements of the selected variables (intraocular pressure, central corneal thickness) were performed before the training session and between 5 and 10 minutes after finishing the exercise. The session lasted 90 minutes. For the statistical analyses, participants were divided according to their sex and age with groups of young adults (≤ 25 years) and adults (> 25 years). Furthermore, participants were stratified into three groups according to their resting intraocular pressure levels (low, medium, or high). For this purpose, preexercise intraocular pressure levels of the sample were divided into terciles (with limits at 14 and 17 mmHg). A mixed-factorial analysis of variance (ANOVA) evaluated differences between groups and between the preexercise and postexercise values. Sex, age, and intraocular pressure levels were included as the between-subject factors. On the other hand, exercise was used as the within-subject factor. In addition, a multiple linear regression was conducted to potentially predict the intraocular pressure variations due to the exercise. The level of significance was uniformly established at p < 0.05. The results of this study show that intraocular pressure levels obtained after the training session were significantly lower than preexercise values (p < 0.001, effect size: 0.73). Central corneal thickness was not significantly modified due to the exercise effect (p = 0.229). It is worth highlighting that baseline intraocular pressure (p = 0.007) and sex (p = 0.001) appeared as significant predictors of the intraocular pressure variations with exercise. More specifically, males, participants older than 25 years, and participants with baseline intraocular pressure levels above 14 mmHg experienced significant decreases in the postexercise values compared with preexercise values (p ≤ 0.001 in all cases, effect sizes between 0.57 and 1.02). In contrast, females, participants younger than 25 years, and participants with resting intraocular pressure levels equal or below 14 mmHg did not show significant intraocular pressure variations after the exercise (significance levels [p] between 0.114 y 0.312). Significant differences in the intraocular pressure variations were observed between the participants with resting intraocular pressure equal to or below 14 mmHg and subjects with resting intraocular pressure equal to or above 17 mmHg (p = 0.008, effect sizes: 0.96). These results confirm that intraocular pressure behavior after exercise is multifactorial. Professionals working with people at risk of suffering high intraocular pressure should account for individual difference such as age, sex, and baseline intraocular pressure levels when programming training adapted to each subject situation. Second study: Characterization of the main squat variations The second article of the compendium, which is presented in Chapter 3, gathers biomechanical, kinetic, and myoelectric information about the most common squat variations (i.e., high-bar back squat, low-bar back squat, front squat, overhead squat, and guided squat). This study aimed to obtain scientific information to select the most appropriate squat variation to be included as a reference in the subsequent studies of the present doctoral thesis. A systematic review of the literature was conducted using four databases and different manual searches. Thirty articles were retrieved after filtering according to the eligibility criteria. The quality of the included studies was assessed with the Physiotherapy Evidence Database (PEDro) scale. All studies obtained scores of between 5 and 6 points out of 6 possible points. Selected squat variations were the high-bar back squat (analyzed by 26 articles), low- bar back squat (analyzed by one article), front squat (analyzed by five articles), overhead squat (analyzed by two articles), and guided squat performed using a Smith machine (analyzed by two articles). Gluteus maximus, gluteus medialis, adductors, vastus lateralis, vastus medialis, rectus femoris, biceps femoris, semitendinosus, tibialis anterior, gastrocnemius, and soleus were included as muscles acting on the hips, knees, and ankles. All variations of the squat exercise begin with the participant in the standing position. Synergistic hip, knee, and ankle flexion is performed followed by extension in the ascent, which ends with the participant in the starting position. The results of the present study indicate that the squat is a knee extensors-predominant exercise, meaning that it mainly exercises the muscles of the quadriceps (vastus lateralis, vastus medialis, rectus femoris, and vastus intermedius). Although the muscles of the quadriceps are the main target of the squat exercise, modifications in the bar placement such as in the low-bar back squat can increase the activity of the hip extensors muscles. Most of the consulted investigations (26 articles) analyzed the high-bar back squat with relatively homogeneous results in terms of activation patterns. The load was identified as the major determinant of muscle activation levels. Furthermore, different technical modifications (movement depth, width of stance, hip rotation, and feet orientation) entailed different activation patterns. After the analysis was performed, the guided high-bar back squat performed using a Smith machine was selected for inclusion in the methodology of the other two studies of the present doctoral thesis analyzing the squat. Concerning the technical execution, parallel depth (as per the lines drawn by the femur and the ground) and neutral positions of stance width, hip rotation, and feet orientation were selected. Third study: The potential of elastic bands to maximize performance in squats The third article of the compendium, which comprises Chapter 4, tests a new method of loading the bar with elastic bands in squats. The pertinent weight that each participant had to use according to their one-repetition maximum percentage was added to the bar at the standing position or just above each participant’s knee sticking point using exclusively elastic bands. Twenty healthy, physically active males, with at least one year of experience in resistance training (age: 25.50 ± 5.26 years; body mass index: 24.09 ± 2.06 kg/m2; body fat: 10.16 ± 2.23%; squat one-repetition maximum: 127.10 ± 24.10 kg; ratio one-repetition maximum to body weight [relative strength]: 1.70 ± 0.36) participated in three sessions: two for assessment and familiarization and one experimental. In the experimental session, six series of squats were performed in random order (three sets using only weight plates to load the bar and three using only elastic bands to load the bar). Four sets (two using weight plates to load the bar and two using elastic bands) were performed until muscular failure, and two sets (one using weight plates to load the bar and one using elastic bands) consisted of submaximal efforts. A goniometer was used to measure the angle of the knee sticking point, and the height of the barbell at this point was marked. Elastic bands were attached to the bar just above this point of the range of motion in the pertinent condition. The weight at the standing position, number of repetitions performed, heart rate, blood pressure, and rate of perceived effort were measured immediately after the completion of each set. An analysis of variance of one-way repeated measurements with Bonferroni adjustments and nonparametric Friedman and Wilcoxon tests were conducted to evaluate differences between the study variables in the different squat conditions. The level of significance was uniformly established at p < 0.05. When weights were equated at the standing position between weight plates and elastic bands, elastic bands permitted participants to perform approximately eight more repetitions (p < 0.001; effect size: 2.44) with the same weight at the standing position (less at the deepest positions), with similar internal load responses (i.e., blood pressure, rate of perceived exertion) compared to weight plates. On the other hand, when weights were equated just above the sticking point between weight plates and elastic bands, elastic bands allowed participants to perform approximately three more repetitions (p = 0.001, effect size: 1.27) with approximately 25% more kilograms (p = 0.001, effect size: 1.15) at the standing position (same kilograms at the sticking point and less kilograms below the sticking point) with similar blood pressure and heart rate responses (p > 0.05). These results confirm that elastic bands could be an optimal material to load the bar for squats for young, trained males. Furthermore, the results suggest that the methodology of adding the pertinent weight just above the sticking point using elastic bands could be useful to increase squat performance. This would be obtained through the overcoming of the biomechanically disadvantageous phase of the squat in which technique is compromised and failure occurs. The findings of this study establish the foundation for future research regarding using elastic bands to improve physical performance. Among other future research lines, medium- or long-term intervention studies should evaluate the potential of the training stimulus provided by the elastic bands attached to the bar immediately above the sticking point in the squat and/or other resistance training exercises to produce chronic adaptations. Additionally, it would be interesting to evaluate whether the same increase in weight and number of repetitions is obtained when directly adding 25% more weight at the participant’s standing position compared to the methodology of loading the bar just above the sticking point. Fourth study: Elastic bands as a device to provoke conservative ocular and cardiovascular responses With the results of Chapters 2, 3, and 4 in mind, the fourth and last published article of the compendium, which comprises Chapter 5, assessed the potential ocular and cardiovascular responses after squatting using elastic bands to load the bar. Additionally, the study evaluated whether these physiological responses were similar compared to those squatting using weight plates. The main aim of the study was to examine ocular (intraocular pressure, ocular perfusion pressure, and central corneal thickness) and cardiovascular (mean blood pressure, pulse pressure, and heart rate) responses produced by squatting using weight plates or elastic bands to load the bar. Furthermore, the responses after a maximal or submaximal effort level were compared. Twenty healthy, physically active males with at least one year of experience in resistance training voluntarily participated in the study (age: 25.55 ± 4.75 years; body mass: 75.67 ± 9.02 kg; body mass index: 24.04 ± 2.11 kg/m2; body fat: 10.19 ± 2.29%; kilograms for one-repetition maximum: 126.53 ± 24.62 kg; ratio one-repetition maximum to body weight [relative strength]: 1.68 ± 0.35). Two sessions were conducted: one for assessment and familiarization and one experimental trial. In the experimental session, the participants performed repetitions to failure and submaximal repetitions at 75% of their one-repetition maximum using weight plates or elastic bands (added at the participants’ standing position) to load the bar. A total of four different sets were performed (two using elastic bands to load the bar and two using weight plates). Preexercise measurements of each cardiovascular and ocular parameter were taken. Each of the four sets was then performed in random order after a standardized warm-up. Cardiovascular measurements were taken immediately after the completion of each set. Ocular measurements were uniformly started one minute after the exercise. An analysis of variance of two-way repeated measurements evaluated differences between the squat conditions performed. The material used (elastic bands or weight plates) and effort level (maximal or submaximal) were used as the within-subject factors. A significance level of p < 0.05 was established. Elastic bands permitted performing more repetitions with the same weight at the standing position (fewer at the deepest phases of the squat) compared to weight plates. Regarding the physiological parameters analyzed related to the present doctoral thesis, intraocular pressure was significantly lower than before the exercise (effect sizes between 0.73 and 1.00). Similarly, mean ocular perfusion pressure (effect sizes between 1.14 and 1.36), heart rate (effect sizes between 2.42 and 2.77), pulse pressure (effect sizes between 0.80 and 1.32), and mean arterial blood pressure (effect sizes between 0.85 and 1.16) were significantly higher compared with preexercise values. On the other hand, central corneal thickness did not significantly vary (p = 0.828). Cardiovascular and ocular responses were similar (p > 0.05) for the use of weight plates (fewer repetitions, more average weight) and elastic bands (more repetitions, less average weight). Although no effect of the material was observed in the ocular variables (p > 0.05), the major intraocular pressure descent (2.70 mmHg) was obtained after performing the maximum number of repetitions with elastic bands; a tendency of statistical significance was observed in the comparison with the condition consisting of a maximal number of repetitions with weight plates (mean difference: 0.55 mmHg, 95% confidence interval [-0.12–1.22], p = 0.10, effect size: 0.21). Therefore, elastic bands seem an appropriate device to load the bar in squats for subjects who should avoid intraocular pressure increments. To supplement these results, future studies should compare intraocular pressure variations throughout the range of motion when using weight plates or elastic bands to load the bar using a continuous monitoring device to differentiate between the movement phases (e.g., concentric and eccentric). Additionally, chronic intraocular pressure and ocular perfusion pressure adaptations to resistance training with elastic bands in healthy subjects, older subjects, subjects at risk of suffering glaucoma, and subjects with diagnosed glaucoma should be evaluated. The findings of the present research suggest that the total amount of work (repetitions x weight) could condition ocular and cardiovascular responses. It is recommended to control technique and movement tempo and avoid the Valsalva maneuver with the aim of maintaining conservative intraocular pressure responses. With this in mind, elastic bands and weight plates could be interchangeably used to load the bar in squats in terms of ocular and cardiovascular responses. Optometrists, ophthalmologists, and strength and conditioning professionals working with people at risk of suffering elevated intraocular pressure or other factors associated with glaucoma development could find the findings of this study useful. Conclusions The findings of the present doctoral thesis shown through the results of the four articles developed establish a foundation for future research with elastic bands from a performance approach. Similarly, results obtained regarding ocular and cardiovascular health parameters open new paths to understanding external (training programming variables) and internal (sociodemographic and physiological) factors potentially conditioning physiological acute adaptations to exercise. Responding to the hypotheses of the present thesis, the main conclusions to highlight are presented hereafter. First, the intraocular pressure after performing an acrobatic gymnastics training session is lower than preexercise values, obtaining significant differences between sexes, age groups, and groups based on baseline intraocular pressure. Baseline intraocular pressure levels and sex were encountered as significant predictors of the intraocular pressure variations provoked by exercise. Second, elastic bands, when attached to the bar with the pertinent weight just above the sticking point, make it possible to use 25% more weight at the standing position and perform approximately three more repetitions compared to weight plates with nonsignificant differences in blood pressure and heart rate. Third, the intraocular pressure after squatting is lower compared with preexercise values, and mean ocular perfusion pressure, pulse pressure, and mean arterial blood pressure are higher with nonsignificant differences between using elastic bands or weight plates to load the bar. The compendium of articles composing the present doctoral thesis illuminates the potential use of elastic bands to maximize performance and maintain conservative ocular and cardiovascular responses. It also contributes to the multidisciplinary collaboration between strength and conditioning professionals, optometrists, and ophthalmologists to raise awareness of the importance of the prevention, management, and control of risk factors associated with glaucoma such as elevated intraocular pressure or fluctuations, decreased ocular perfusion pressure, and increased or decreased blood pressure.