Design and hypotheses
This is a three-arm randomized crossover clinical trial. The study will involve 40 male volunteers aged between 20 and 30 who will be assessed in 3 meetings at one-week intervals to see if HG modifies the acute response of heart rate, systolic and diastolic blood pressure, and the double product. We hypothesize that HG will be able to attenuate the fall in DBP during CE by at least 5mmHg, raise HR values by 10bpm, SBP by 10mmHg and SD by 1,000 units. We also hypothesize that there will be an increase of at least two units on the Borg scale (6-20).
The protocols will be carried out in an air-conditioned room at 23ºC in the school clinic of the Adventist College of Bahia. The collection period began in November 2023 and is expected to be completed by December 2024 (Figure 1).
Figure 1. The study protocol based on Standard Protocol Items: Recommendations for Interventional Trials (SPIRIT). P1: Protocol I (without handgrip); P2: Protocol II (with handgrip with a load of 30% of handgrip strength); P3: Protocol III (handgrip with a load of 60% of handgrip strength).
Recruitment
The sample will be made up of university students from the Adventist College of Bahia and will be recruited through digital and printed posters on social networks and on the institution's premises. Screening meetings will be held on Mondays and Wednesdays, as scheduled, throughout the research period. All volunteers will be informed about the study proposal, risks, benefits, and the necessary precautions for participation. Volunteers will be made aware of the possibility of discontinuing their participation in the study at any time, without charge to the participant. In addition, the researchers will contact the participants by telephone to let them know when the research meetings will take place and if they have any questions.
Eligibility Criteria
Young adults aged between 18 and 30, classified as active or irregularly active by the International Physical Activity Questionnaire (IPAQ) - Short Version [11], will be included. Individuals will be excluded if, based on the preliminary health assessment, they have limiting conditions reported in the medical history questionnaire or if they are classified as being at high risk of cardiovascular disease, with two or more risk factors, according to the guidelines for stress tests and their prescription of the American college of sports medicine [4]. Individuals who report pre-existing musculoskeletal disorders that make it impossible to perform the exercise protocol will also be excluded.
Those who meet the eligibility criteria will receive verbal and written information about the study protocol and will be invited to take part in the next stages of the research by signing the Free and Informed Consent Term (FICT).
Instruments used
The following equipment will be used during the study:
- Welmy digital scale, with a maximum capacity of 200 kg and a stadiometer with an accuracy of 0.1 cm, certified by the National Metrology Institute (INMETRO);
- Polar H10 cardiofrequency meter (Polar Electro Oy, Kempele, Finland) [12];
- 3M™ Littimann® classic III™ stethoscope (3M do Brasil Ltda, Sumaré, SP, Brazil);
- Welch Allyn DS44-11BR Durashock sphygmomanometer (Welch Allyn, Barueri, SP, Brazil);
- EKO CORE MD™ auscultation amplifier (Eko Devices, Inc - Berkeley, California, USA), capable of amplifying sound up to 40 times, real-time transmission, and audio recording via Bluetooth;
- Jamar® hydraulic handheld dynamometer (Model J00105, Lafayette Instrument Company, Lafayette, Indiana, USA) [13];
- Handgrip device (Brother Medical, China) with a load of 5 to 40 kg;
- Athletic Extreme 3260T 18km/h treadmill (Athletic Comercio LTDA, São Paulo - SP).
Physical and clinical assessment
Immediately after screening, a physical-clinical assessment will be carried out, with sociodemographic data being filled in, followed by a physical examination. The physical examination will include an assessment of height and weight, which will determine the body mass index (BMI - weight/height²). In addition, resting HR will be recorded using a Polar® H10 cardio-frequency meter [12] and Blood Pressure (BP), which will follow the recommendations of the American Heart Association [14].
Determination of Handgrip Strength (HGS)
To determine the HGS, the recommendations of the American Society of Hand Therapists [13] will be followed, using the Jamar® hydraulic dynamometer. The volunteer will be instructed to remain in a supine position and perform a maximum palmar contraction with the elbow flexed to 90º and the forearm in a neutral position. Three attempts will be made on each hand, with a one-minute rest between attempts. The highest values on each side will be recorded, and the measurement of the weaker arm will be selected to calculate the load used in the interventions.
Treadmill stress test
We will carry out an incremental exercise test on a treadmill to determine the speed required for the volunteer to reach the light and moderate training zones, at 30% and 50% of the reserve HR, respectively. The test will start at a speed of 2 km/h, with a gradual increase in speed to 4 km/h during the first 3 minutes of the test. Subsequently, the speed will be increased by 1km/h every minute. The target heart rate zones will be determined using the Karvonen equation: resting heart rate + (maximum predicted heart rate - resting heart rate) x % intensity. The maximum predicted heart rate for the calculation will be determined by the equation 220 - age, which in the chosen age group is the most accurate equation [15]. During the test, heart rate will be monitored using a cardiac transmitter combined with a Polar H10 cardiac sensor [12]. The speed for the protocol's target zone will be considered to be when the volunteer reaches and sustains, for at least 10 seconds, an HR 5bpm above or below the value stipulated by the equations.
Sample randomization
Randomization will be carried out simply and randomly by drawing numbered balls from 1 to 3, taken from a black bag by the volunteers. Each number will represent an exercise protocol to be carried out. The volunteer will draw the first ball to represent the protocol to be carried out in the first week, a second ball to represent the protocol for the second week, and the remaining ball to determine the protocol for the third week. The protocols will be carried out one week apart. Figure 2 shows the selection and randomization process for the three study arms.
Figure 2. Flow diagram of sample selection and internal randomization throughout the study
P1: protocol I (without handgrip); P2: protocol II (with handgrip with a load of 30% of handgrip strength); P3: protocol III (handgrip with a load of 60% of handgrip strength).
Blinding
Due to the nature of the exercise intervention and the instrument used in the interventions, it will not be possible to completely blind the sample and the evaluators. The volunteers will be identified by groups that will alternate between the interventions, thus minimizing confounding bias. In addition, volunteers will be identified by number, two researchers will be responsible for allocation control, data recording, and general conduct of the study, while a single evaluator will be responsible for the hemodynamic assessments. The latter will not be informed about the group or protocol followed by the participant.
Intervention
The protocols will be divided as follows: five minutes at rest to assess resting HR and BP, then the volunteer will be taken to the treadmill where they will warm up for three minutes at a speed of 30% of reserve HR. Subsequently, the participant will be subjected to four 2-minute sprints at a speed of 50% of reserve HR, separated by one-minute intervals at the same speed as the warm-up. Systemic blood pressure and HR will be measured in the final 20 seconds of each sprint, and during the active intervals of the sprints, the participants will be asked about their subjective perception of effort using the Borg scale (6-20).
At the end of the 4th sprint, we will start the two-minute warm-up phase, the first minute at the warm-up speed and the next with a progressive reduction to the minimum speed of the treadmill. The BP, HR, and Borg variables will also be collected immediately after the effort, in the first, third, and fifth minutes of rest.
Differentiation of protocols
While Protocol I will follow the coordinates described above, Protocols II and III will add bilateral isometric contraction with an HG device during the sprints, at loads of 30% and HG 60% of the manual grip force obtained in the test, respectively. Figure 3 shows the stages of the interventions.
Figure 3. Stages of the intervention protocols
HRR: Heart Rate Reserve; HGS: Handgrip strength; HG: Handgrip;
Heart rate, systolic blood pressure, diastolic blood pressure, and perceived exertion (BORG 6-20) will be measured during stages 1, 3, and 4, in stage 3 at the end of each sprint and in stage 4 immediately, 1, 3 and 5 min after the effort.
Hemodynamic monitoring during the intervention
HR measurements will be recorded using a Polar H10 cardiofrequency meter [12] every minute and blood pressure measurements will follow the recommendations of the American Heart Association [14]. To increase safety when assessing blood pressure-related outcomes, a stethoscope will be used with an auscultation amplifier attached to the stethoscope.
During SBP monitoring, the assessor will be positioned on the left side of the treadmill. The sphygmomanometer will be kept on the volunteer's left arm throughout the protocol. The sphygmomanometer's clock will be supported by a metal bracket in order to avoid mechanical oscillations. At the time of measurement, the volunteer will be asked to maintain running speed and rest their left arm on the evaluator's shoulder, thus remaining with the limb extended and relaxed in a position of approximately 90º for shoulder flexion, with the forearm and hand supine. In addition, for the protocols using the HG, the volunteers will be instructed to stop the isometric contraction on their left side, handing over the device when the SBP is measured.
To determine SBP values, the evaluator will inflate the sphygmomanometer cuff while performing the auscultation. The device will be inflated by an average of 20mmHg/s until no sound is heard. From this point on, the assessor will inflate another 20mmHg and then open the valve, allowing the air to escape and reducing the pressure by 10mmHg/s. During the assessment, SBP and DBP will be determined by the first and fifth phases of the Korotkoff sounds, respectively [14].
Predictor variables
Isometric contraction with HG: the presence of HG during the cyclic exercise protocol and the established load will be factors that differentiate the protocols, thus separating the 3 research groups.
Time of exposure to exercise: During the protocol, there may be a difference between the moments of evaluation due to the action of time on hemodynamic function and perception of effort. The data will be processed to differentiate between changes caused by HG and those resulting from exposure to exercise time.
Level of physical activity: It will be investigated whether the level of physical activity causes changes in the research outcomes.