This quantitative research study was designed as a randomised, repeated-measures experiment. The independent variables for this study were interval training protocol and time, with primary interest being the effect of protocol on physiological changes. The intensity of each 1:1 work-to-recovery ratio was calculated as a percentage of PPO achieved during an incremental test to fatigue. The treatment protocol intensities were 80%:0%, 80%:50%, 100%:0%, and 100%:50% of PPO. The dependent variables measured were oxygen uptake (VO2), heart rate (HR), blood lactate concentration (bLa), and rating of perceived exertion (RPE).
Participants Selection and Exclusion Criteria
… participants passed the initial screening criteria and were accepted into the study. No subjects were dropped from the study for failing criteria or from any adverse effects from the study protocol. Ten healthy, recreationally active adults (… males, … females) selected from Leeds Beckett University, Carnegie Faculty (age = … ± …) participated in this study and were included in the final data analysis. Participants were recruited via email and enrolled on a voluntary basis. The inclusion criteria for this study were determined by a health history form and physical activity readiness questionnaire (PAR-Q; Garber et al., 2011). In order to be accepted into the study, each participant could answer positively to one of the questions in the health history form (Appendix A). These criteria were used to define a “low-risk” subject. All subjects that were accepted into this investigation signed an informed consent waiver (Appendix B). All protocols were approved by Leeds Beckett University Local Research Ethics Committee.
Internal and External Validity
The internal validity of this study was maintained through the use of a controlled laboratory environment (temperature = … ± …, humidity = … ± …). In addition to this, the four different HIIT protocols were assigned to participants in a randomised order (Mention the treatment order sheet?). All protocols were separated by a minimum of 48 hours. All participants volunteered and none of the participants were selected for a particular trait, capability, or physical characteristic. The internal validity was not threatened by testing history because all of the protocols that were performed in this study were novel to the participants, and the participants did not perform any of the treatment protocols more than once. The instruments used for data collection were always calibrated before each use and the same investigator administered all experimental tests. This experiment utilised standard testing procedures and uniform physiological measures of VO2, HR, bLa, and RPE. Participant compliance was sustained by conveying pre-test instructions asking each participant to abstain from vigorous exercise for 24 hours prior to testing, and to wear clothing that allowed for greatest mobility during exercise. If a subject did not meet the criteria they were asked to complete the protocol at a forthcoming date.
Threats to the external validity of the experiment were controlled in order to limit error in generalisation of the results. Although each treatment protocol was comparable in duration, all protocols varied in the intensity of work and recovery. This limited the ability to “learn” how to perform better when participating in the different protocols. The results of the experiment were not discussed until after the participant finished all four treatment protocols, which limited any motivating factors the participant may have experienced. As aforementioned, all participants were recruited voluntarily and were not picked for a specific attribute in order to limit selection bias. Selection bias is defined by purposely picking participants in order to observe a desired result. No distinct attention was given to any of the participants in this study. This was maintained in order to limit the Hawthorne effect of enhanced performance due to increased attention. – Similar study wrote this within their methodology, necessary statement for this study?
Instrumentation
Cycle Ergometer
Exercise was performed using an electronically braked cycle ergometer (Corival 906900, Lode BV Medical Technology, Groningen, The Netherlands) that maintained constant work rate under variable pedal rates. Neither the pedals nor the handlebars on the ergometer were altered in any way in order to produce an advantage for a single participant. Prior to the graded exercise test a comfortable seat height was recorded and used during each subsequent exercise session.
Anthropometric and Baseline Data Collection
The following anthropometric and baseline data were collected on all participants: height, body mass and blood pressure. The subject’s height was collected with a floor-mounted stadiometer (Seca, 222, Germany). The subject’s body mass was measured using digital floor scales (Seca, Alpa 770, Germany). Blood pressure was measured during screening, using a stethoscope and green light electronic manometer sphygmomanometer (Accoson, Greenlight 300, England), after 5 minutes of rest in the seated position.
Physiological Measures
Assessment of Blood Pressure
Preceding the start of the GXT and all subsequent high-intensity exercise protocols, each participant was asked to rest in the seated position for at least 5 minutes. Using a stethoscope and green light electronic manometer sphygmomanometer (Accoson, Greenlight 300, England), blood pressure was evaluated in order to observe any adverse signs of hypertension or hypotension. Blood pressure was not used as an outcome measure in this study and was obtained to compare to the initial pre-test value in order to determine uniformity of blood pressure. No participants were determined to be hypertensive or hypotensive.
Blood Glucose and Total Cholesterol
Initial screening required the analysis of total cholesterol and resting blood glucose. Extraction of blood was carried out at the fingertip by safety lancet (HaeMedic, Haemolance Plus, Poland) and analysed for total cholesterol using an Accutrend device (Roche, Accutrend Plus, Germany). Blood glucose was analysed using the YSI blood analyser (YSI, 2300 Stat Plus, USA) that was calibrated using a buffer solution (range of buffer solution) as instructed by the factory guidelines. – Is this paragraph necessary?
Gas Analysis
Gas analysis was recorded using breath-by-breath online gas analysis system (Cortex, Metalyzer 3B, Germany). Inspired air was collected through a pliable, rubber mask fitted to the participant. The researcher and participant determined the correct sizing of mask during the first exercise session and this was recorded for subsequent use. Calculation adjustments were made to data according to the size of the mask being used.
Heart Rate
HR data was collected via a polar wireless heart rate monitoring system (Polar®, Wearlink, Finland). The heart rate monitor was able to connect to the online gas analysis software and produce a heart rate value (bpm) for each breath. Heart rate data was collected throughout the duration of the test and reported in 20s averages.
Blood Lactate Assessment
A preliminary bLa sample was attained prior to the start of exercise for both the GXT and all subsequent exercise protocols. A midpoint bLa sample was obtained for all treatment protocols but not for the GXT. A post-test bLa sample was obtained immediately after test termination in the GXT and immediately after the last “recovery” period for all exercise protocols. BLa samples were taken at the fingertip with a single-use safety lancet, in order to collect a small sample of blood. After the subject’s finger had been punctured, the blood sample was analysed using a blood lactate analyser (YSI, 2300 Stat Plus, USA). All blood samples were obtained using Leeds Beckett University laboratory procedures and safety considerations for the handling of biological fluids. Leeds Beckett University standard laboratory blood consumables kit was used for fingertip blood extraction. This included:
• Capillary tubes (Analox, Germany)
• Alcotip swabs (UHS, England)
• Safety gloves (St. John Ambulance, Powder free examination gloves, England
• Tissues (Terinex, Cloudsoft, England)
• Waterproof plasters (Steroplast, Sterostrip-waterproof, England)
Blood samples were taken with the subject sitting on the bike after the gas analysis mask had been fitted. Before use on each participant, the analyser was calibrated using a calibration buffer solution (buffer solution range (mmol/L)) as instructed by the factory guidelines.
Subjective Measures
Rating of Perceived Exertion
Throughout the entire exercise portion of the GXT and all subsequent treatment protocols, the participants’ RPE (Borg, 1970; Appendix) was obtained after each minute of exercise. Before the start of exercise each participant was informed on the range of the RPE scale and how to use it during the test. The Borg (1970) scale ranges from 6 (very, very light) to 20 (very, very hard) and the participant was asked to point to an associated value of subjective fatigue after each minute of exercise. In order to minimise confusion during the exercise sessions, each subject was asked to point with their finger to the associated RPE rather than speaking with the gas analysis mask fitted.
Pre-Participation Procedures
All procedures used during this study were approved by a Leeds Beckett Local Research Ethics Coordinator. The researcher was instructed on University laboratory procedures including biomedical waste precautions and appropriate disposal techniques. Prior to the study, participants were provided with an information sheet outlining the protocols to be used, potential risks involved, and potential benefits of the study (Appendix C). Participants were then required to sign an informed consent waiver (Appendix). In accordance with the University’s policy to protect subject confidentiality, each subject was allocated a unique identification number known only to the primary researcher. Physical records acquired from data collection were held under lock and key that only the principal researcher had access to. All other records were kept digitally as password protected files upon a USB memory unit. All data collection took place in the Exercise Physiology Labs at Leeds Beckett University. The laboratory temperature ranged from … to … degrees Celsius and humidity was between … and …. Testing was completed over the course of six separate sessions separated by at least 48 hours. The first session was used to determine inclusion of a subject into the study. If a subject was accepted they were then considered a participant and their aforementioned baseline anthropometric data was recorded for inclusion in the study. The participant was then familiarised with the equipment, testing procedures, and time commitments. Participants were asked to refrain from vigorous exercise, alcohol or caffeine intake 24 hours prior to testing. This was ensured through a pre-exercise questionnaire completed before each exercise session (Appendix).
The Graded Exercise Test
The second session tested the participant’s cardiopulmonary fitness (VO2p), HRpeak, blood lactate concentration, and rating of perceived exertion (RPE). The graded exercise test (GXT) was used to determine each subject’s cardiopulmonary fitness and PPO. The participant was familiarised with the procedure and then fitted with a pliable, rubber mask used to collect expired gases during each breath. The participant and researcher then determined the most optimal seat height and recorded that value for subsequent use. Before the start of exercise or gas analysis, a resting blood lactate concentration was measured with the participant in the seated position on the cycle ergometer. The GXT began with 2 minutes of rest followed by 2 minutes warm up of unloaded pedalling. Immediately following warm-up the work rate increased continually, by a pre-determined rate until voluntary exhaustion. Work rate increment was calculated using a modified version of the Wasserman et al. (year) equation. However, this equation was developed using a sedentary population and consequently, an addition of 5W to the predicted WRI was determined, during pilot testing, to elicit a more accurate VO2p in the recreationally active individuals of this study. Males and females also had marginally different workload increments, accounted for in the Wasserman et al. (year) prediction equation. Immediately following cessation of exercise, the participant began actively recovering at a work rate of 25W for a total of 5 minutes. The highest mean 20s of oxygen uptake was used as the participant’s peak value (V02p). The power output associated with this V02p value, which the participant could maintain for 20s, was recorded and defined as their PPO. This value was used for subsequent calculations. The PPO achieved during the GXT was used to calculate the percentages of “work” and “recovery” that each participant would be prescribed during the four treatment protocols. The target work rates for the work period of the high-intensity interval were 80% and 100% of the PPO, and 0% and 50% during the periods of recovery. Due to a limitation of the software being used to control the electronically braked cycle ergometer, if a percentage of the PPO fell on a value that was not whole number, then the workload was rounded to the nearest whole value. An electronically braked cycle ergometer was used for all GXTs. Because the cycle ergometer was electronically braked, participants were asked to stay within a pedal rate of 50-120 revolutions per minute, which is the controllable range on the ergometer. This rate was visibly observed on a colour-coded, green region located on the face of the ergometer. The participants were asked to stay in the “green” region throughout the duration of the test. If, during the GXT, the participant could not stay within the needed range then the test was terminated. After termination of exercise the participant began actively recovering at a work rate of 25 W for a total of 5 minutes. During this time a post-test blood lactate concentration measurement was obtained. The participant was observed for signs and symptoms of lethargy, confusion, or discomfort. Heart rate was recorded continuously for the entire duration of the test. RPE was recorded immediately after the first minute of exercise and at the end of every minute thereafter until exercise termination.
High Intensity Interval Protocols
In the subsequent four exercise sessions, each participant performed the high-intensity interval treatment protocols in random order. A treatment order counterbalancing table was developed by the researchers to ensure randomisation of treatment order (Appendix). The participant completed a pre-exercise screening questionnaire before each exercise session (Appendix) and was assessed for blood pressure and resting heart rate. Each participant was then seated on the cycle ergometer and fitted with a gas analysis mask. A resting blood lactate concentration was then measured before exercise or gas analysis began. All protocols were preceded by 2 minutes of rest and then 5 minutes of unloaded pedalling as a warm up period. Immediately after the warm up the participant began the protocol that was randomly assigned. Each protocol was 20 minutes in duration, which alternated between 1-minute periods of work and recovery. For all protocols, each participant completed 10 bouts of work and 10 bouts of recovery. During all periods of exercise the participants were in the seated position and were allowed to stand only momentarily to adjust their position. The participants were asked to refrain from talking during the protocol unless they needed to instruct the investigators to terminate the test. The investigators minimised communication with the participant to limit external motivation. VO2 and HR were measured continuously throughout the duration of the test and RPE was measured immediately after each minute of work and recovery. BLa was obtained at the midpoint of the interval protocol and a post-exercise bLa was acquired immediately after the final period of recovery. Following cessation of the test the participant was evaluated for any adverse signs or symptoms. Based on the standards of intensity given by ACSM (Garber et al., 2011), all protocols were determined to be of moderate to high intensity.
Data Analysis
Mean values and standard deviations were calculated for VO2, HR, bLa, and RPE. VO2 and HR were expressed as a percentage of their peak values. Because this was intermittent exercise with high intensities during periods of work and low intensities during periods of rest, means and standard deviations were also reported for the peaks and nadirs of VO2, HR, and RPE. The peaks and nadirs were defined as a value representing the final 20s of each minute that corresponded with the work or recovery period, regardless of any further increase in value after that point in time. Confidence intervals were reported for all aspects of VO2 and HR. The data were organised and tables were created with Microsoft Excel (2010). An initial one-way analysis of variance (ANOVA) was performed using SPSS (SPSS Statistics Version 20, SPSS, Chicago, USA). A Bonferroni correction was used to correct for the error rate when making multiple comparisons. For all statistical evaluations, a P-value less than or equal to 0.05 (p < 0.05) was considered significant.