Performance and Recovery of Well-Trained Younger and Older Athletes during Different HIIT Protocols

to physiological and morphological differences, younger and older athletes may recover differently from training loads. High-intensity interval training (HIIT) protocols are useful for studying the progression of recovery. It was the objective of this study to determine age differences in performance and recovery following different HIIT protocols. Methods: 12 younger (24.5 3.7 years) and 12 older (47.3 8.6 years) well-trained cyclists and triathletes took part in this study. Between the age groups there were no signi cant differences in relative peak power to fat-free mass, maximal heart rate (HR), training volume, and VO 2max-percentiles (%). Participants performed different HIIT protocols consisting of 4 30 s Wingate tests with different active rest intervals (1, 3, or 10 min). Peak and average power, lactate, HR, respiratory exchange ratio (RER), subjective rating of perceived exertion (RPE), and recovery (Total Quality Recovery scale, TQR) were assessed. Results: During the different HIIT protocols, metabolic, cardiovascular, and subjective recovery were similar between the two groups. No signi cant differences were found in average lactate concentration, peak and average power, fatigue (%), %HRmax, RER, RPE, and TQR values between the groups (p>

ratio (RER), subjective rating of perceived exertion (RPE), and recovery (Total Quality Recovery scale, TQR) were assessed. Results: During the different HIIT protocols, metabolic, cardiovascular, and subjective recovery were similar between the two groups. No signi cant differences were found in average lactate concentration, peak and average power, fatigue (%), %HRmax, RER, RPE, and TQR values between the groups (p> 0.05). Conclusion: The ndings of this study indicate that recovery following HIIT does not differ between the two age groups. Furthermore, older and younger participants displayed similar lactate kinetics after the intermittent exercise protocols. Keywords: aging; master athletes; endurance exercise Wingate test; HIIT; interval training; cycling; recovery; lactate; heart rate recovery 1. Introduction Recovery from exercise is essential for continuous performance improvement [1,2]. Due to morphological and physiological changes occurring during aging and age-related alterations in performance capacity, younger and older athletes may recover at different rates from physical exercise and training loads [3–5]. Age-related physiological and morphological changes in the muscular system include the selective loss of fast muscle bers and motor units, along with a decrease in muscle cross-sectional area and number of satellite cells, and a change in muscle architecture[6,7]. Maximum oxygen uptake decreases in both untrained and trained older subjects [7]. How- ever, trained subjects with a higher physical tness level are able to maintain this higher level compared with untrained subjects [8]. It is well established that maximal heart rate (HRmax) decreases with age and is independent of sex [9]. The maximum lactic acid production rate, which is determined by the performance capacity or trainability of the fast muscle bers [10], decreases with age [11]. Although peak blood lactate levels of trained subjects are considerably higher than those reported for untrained subjects, anaerobic energy production from glycolysis Sports2022,10, 9.

Sports2022,10, 9 2 of 14 declines with older age. This may be a factor responsible for the deterioration in sprint performance [12]. A decrease in muscle mass and shift towards a more oxidative muscle pro le mediated by the atrophy of fast-twitch bers during aging [6] indicates a reduced creatine phosphate metabolic capacity, in addition to a decreased rate lactic acid formation and glycolysis. It may also be possible that the anaerobic energy output decreases with aging due to a reduction in important glycolytic enzymes, particularly phosphofructokinase [13]. Further- more, glucose transporter (GLUT-4) levels decrease with aging, reducing glucose transport ef cacy, possibly affecting performance and recovery in older athletes [14]. Therefore, training adaptation, decline in performance, and recovery in the process of aging varies among different sports and intensities of exercise. According to Fell and Williams [3], an older athlete may require a more extended post-exercise recovery period compared to a younger athlete with a similar performance level when applying the same training load. The extent to which age-related physiological and morphological differences affect recovery in aging athletes during high-intensity interval training (HIIT) sessions with different recovery periods has not yet been investigated. HIIT sessions are used to improve maximum oxygen uptake (VO2max) and endurance performance in high-performance and recreational sports [15–17]. High-intensity inter- val training (HIIT) protocols are variable in their design and can be different regarding the number of repetitions, duration of intervals, intensity, and recovery time between interval bouts, thereby pursuing different training goals [18,19]. Postexercise recovery is a multifaceted (e.g., psychological, physiological) restorative process and an essential component of exercise training. Recovery is crucial to allow for continuous performance development [1,2,20]. The length of recovery time does not only in uence the maximal performance during each exercise bout, but also the overall organismic stress [21–23]. Due to their intermittent character, HIIT sessions are useful for studying the progression of recovery. Recovery following repeated sprint and endurance exercise is different in children and adults. Children have a shorter lactate half-life as a result of their lower maximal lactate concentrations, and a faster heart rate recovery (HRR)

each exercise bout, but also the overall organismic stress [21–23]. Due to their intermittent character, HIIT sessions are useful for studying the progression of recovery. Recovery following repeated sprint and endurance exercise is different in children and adults. Children have a shorter lactate half-life as a result of their lower maximal lactate concentrations, and a faster heart rate recovery (HRR) and respiratory recovery compared to adults [21,24–27]. Most studies on post-exercise recovery have either compared children and adults or younger and older athletes with different performance levels [5]. Studies with a different level of performance or training status revealed delayed recovery of VO2and VCO2for master athletes compared to adults [28]. Studies on recovery following continuous endurance exercise (running competition) in younger and older athletes (masters) with matching performance levels (VO2max) revealed a delayed muscular recovery and greater muscular damage during recovery in masters (45.9 5.9 years) compared to younger athletes (30.5 7 years) [4]. However, no studies have been conducted on recovery during and after high-intensity intermittent exercise in younger and older adults with matched performance levels. The Wingate anaerobic test (WAnT) comprising four 30 s maximal efforts on a cycle ergometer allows for continuous measurement and recording of heart rate (HR), oxygen up- take, and power [29–32]. The length of 30 s for short intervals is suitable for the evaluation of anaerobic performance, as shown in many studies on maximal exercise [21,23,31–33]. Furthermore, this allows for a differentiated and comprehensive discussion of the nd- ings of this present investigation with previous ndings, and for a derivation of practical applications for athletes and coaches. HIIT is used in elite sports, tness sports, and recreational sports in a number of ways, and the training design of HIIT sessions, especially the duration of recovery phases, has a direct impact on performance development. However, to date, no comprehensive evaluation has been conducted on whether younger and older athletes respond and recover in a similar manner. Therefore, this study examined a younger and an older group of athletes whose physical performance was comparable. This has not been taken into account

of recovery phases, has a direct impact on performance development. However, to date, no comprehensive evaluation has been conducted on whether younger and older athletes respond and recover in a similar manner. Therefore, this study examined a younger and an older group of athletes whose physical performance was comparable. This has not been taken into account

Sports2022,10, 9 3 of 14 in previous studies, in which older athletes typically had a lower performance level and, as a result, their recovery was reduced. However, this study compared the recovery of younger and older athletes with matched physical performance levels. The aim of this study was to examine possible age-speci c differences in cardiovascular, metabolic, and subjective recovery during HIIT with active recovery times of different durations between intervals. Moreover, the study investigated whether different recovery times in uence the performance of younger and older athletes during HIIT. 2. Materials and Methods 2.1. Participants Two groups consisting of 12 younger (mean age: 24.5 3.7 years; 8 men, 4 women) and 12 older athletes (mean age: 47.3 8.6 years; 8 men, 4 women) took part in this study. For at least six months prior to taking part in the study, all athletes were required to cycle for at least 6 h/week and have a VO2maxabove the 80th percentile [34]. The baseline values of the 24 athletes are shown in Table. There were no signi cant differences in height, body mass, and fat-free mass (FFM), or in the performance-related parameters HRmax, relative peak power output to FFM, and weekly training volume between younger and older athletes. Younger and older athletes had a comparable maximal aerobic performance capacity according to sex and age-speci c VO2maxpercentiles [34]. The bioimpedance values showed age differences for body fat but not for FFM. There were no signi cant differences in the bioimpedance data of the athletes between the testing days. Table 1. Anthropometric data, exercise performance parameters, and maximal heart rate (HRmax), of the athletes at baseline measurements. Data are means SD. Parameter Younger Athletes (n= 12) Older Athletes (n= 12) p-Values Age (years) 24.5 3.7 47.3 8.6 <0.001 Height (m) 1.76 0.11 1.72 0.11 0.423 Body mass (kg) 65.9 10.9 70.8 11.0 0.281 BMI (kg/m 2 ) 21.1 1.8 23.7 2.2 0.004 Body fat (%) 9.8 6.3 14.9 6.1 0.011 FFM (kg) 59.8 12.0 59.3 9.5 0.901 VO 2max(mL/min/kg) 56.7 7.0 49.2 6.4 0.011 HRmax(min 1 ) 179.2 11.1 174.9 11.7 0.371 Peak Power

3.7 47.3 8.6 <0.001 Height (m) 1.76 0.11 1.72 0.11 0.423 Body mass (kg) 65.9 10.9 70.8 11.0 0.281 BMI (kg/m 2 ) 21.1 1.8 23.7 2.2 0.004 Body fat (%) 9.8 6.3 14.9 6.1 0.011 FFM (kg) 59.8 12.0 59.3 9.5 0.901 VO 2max(mL/min/kg) 56.7 7.0 49.2 6.4 0.011 HRmax(min 1 ) 179.2 11.1 174.9 11.7 0.371 Peak Power (W/kg) 5.24 0.58 4.66 0.43 0.011 Peak Power (W/kg FFM) 5.79 0.47 5.60 0.71 0.122 VO 2max-percentile (%) 95.4 5.2 93.1 5.8 0.326 Training (h/week) 8.73 3.62 8.37 2.28 0.627 This investigation was approved by the Martin-Luther-University Halle-Wittenberg Ethics Committee (Reference code: 2019-094) and conducted in accordance with the Decla- ration of Helsinki. 2.2. Test Protocol Each test took place under standardized conditions of a 20 C lab temperature and 55% relative humidity. Subjects reported to the laboratory on four occasions. They had to be in a recovered and hydrated state after having fasted for at least two hours. Additionally, they had to abstain from strenuous exercise for 48 h prior to all tests. Every athlete was tested again at the same time of day, and all cycling tests were conducted on the same cycling

Sports2022,10, 9 4 of 14 ergometer during each visit. During the entire course of the study, all athletes agreed to maintain their usual dietary habits and to document their daily training load. On the rst of four visits, baseline assessments took place. Subjects completed a medical questionnaire and indicated they had not taken any supplements or medication that could in uence the results. Body composition (body mass, FFM and body fat) was determined after 20 min in the supine resting position using a Bio Impedance Analyzer (Data Input GmbH, Pöcking, Germany). Then, a Metalyzer 3B (Cortex, Leipzig, Germany) was applied in an incremental step test until voluntary exhaustion on an elite bicycle ergometer (E 2000s, FES, Berlin, Germany) to determine the athlete's aerobic tness in terms of oxygen uptake. This test started with a warm-up over eight minutes at 70 W for female athletes and at 100 W for male athletes on the cycling ergometer. After the warm-up, athletes completed the VO2maxtest [35,36]. Thereby, all athletes started with a resistance of 70 W and, each minute, the power increased by 30 W. For all athletes, the cadence was set at 80–90 rpm throughout the entire test. One week following the baseline test, athletes completed the rst of three HIIT sessions. Thereby, a 30 s WAnT was performed four times, separated by different active recovery periods at each visit (1, 3, or 10 min) as displayed in Figure. The athletes performed the three different HIIT protocols under standardized conditions in a randomized order regarding the three recovery times (1, 3, or 10 min). Each test was separated by one week of recovery. The power for the warm-up, active recovery periods, and cool-down was set at 70 W for female athletes and at 100 W for male athletes, with a cadence of 80–90 rpm. Using 10 L of blood taken from the ear lobe, lactate levels were measured with the enzymatic-amperometric method (Mueller, model Super GL ambulance, Freital, Germany). Throughout all tests, beat-to-beat (RR) intervals and the HR using an HR monitor (RS800 CX and Polar WearLink W.I.N.D., Polar Electro GmbH, Büttelborn,

at 100 W for male athletes, with a cadence of 80–90 rpm. Using 10 L of blood taken from the ear lobe, lactate levels were measured with the enzymatic-amperometric method (Mueller, model Super GL ambulance, Freital, Germany). Throughout all tests, beat-to-beat (RR) intervals and the HR using an HR monitor (RS800 CX and Polar WearLink W.I.N.D., Polar Electro GmbH, Büttelborn, Germany) and gas exchange using a Metalyzer 3B (Cortex, Leipzig, Germany) were continuously recorded. The subjective rating of exertion and state of recovery were determined using the Rating of Perceived Exertion (RPE) scale [37] and the Total Quality Recovery scale (TQR) [38]. The RPE value of the athletes was assessed after each of the four WAnT intervals, and the TQR value after every active recovery period and every three minutes during the 15 min cool-down. The testing protocol with the measurement points is shown in Figure. The testing protocol was used in an extensive investigation on sex and age differences with different subject groups during HIIT using a consistent study design. The results regarding sex differences have already been published [23]. For lactate determination, capillary blood was taken before the start of the HIIT protocol after a standardized warm-up and at the measurement points M2, M4, M6, and M8 (Figure). The standardized warm-up consisted of 8 min cycling at 70 W for females and 100 W for males, and the cadence was set at 80–90 rpm. The RPE values [35] were recorded at the measuring points M2, M4, M6, and M8. The TQR values [36] were recorded at M3, M5, and M7. Throughout the 10 min active recovery period, blood for lactate determination was also taken. During the 15 min active cool-down, lactate concentration and the TQR rating were determined at 3, 6, 9, 12, and 15 min. Continuous recording of power, ventilatory parameters (breath by breath), and HR (beat to beat interval) took place throughout the entire test period. Intraindividual fatigue, as the respective performance decline within each of the WAnTs over the 30 s duration, was calculated using the formula: %fatigue = (peak powerWAnT average powerWAnT)/peak powerWAnT 100)

at 3, 6, 9, 12, and 15 min. Continuous recording of power, ventilatory parameters (breath by breath), and HR (beat to beat interval) took place throughout the entire test period. Intraindividual fatigue, as the respective performance decline within each of the WAnTs over the 30 s duration, was calculated using the formula: %fatigue = (peak powerWAnT average powerWAnT)/peak powerWAnT 100) [39].

Sports2022,10, 9 5 of 14 Figure 1. Testing protocol of the Wingate anaerobic tests (WAnT) during high-intensity interval training (HIIT). The three different protocols with four Wingate tests each, regarding the three active recovery times at 70 W for females and 100 W for males (1, 3, or 10 min active recovery) were performed in a randomized order with one week recovery between (M1–M8: measurement points). 2.3. Statistical Analysis Descriptive statistics of the data are presented as mean standard deviation (SD). Statistical analysis was conducted with IBM SPSS Statistics (version 25, International Business Machines Corporation, Armonk, NY, USA) and a published spreadsheet [40]. A repeated measures two-way ANOVA with Bonferroni corrections for multiple comparisons was used to detect interaction effects if warranted. Univariate post hoc analyses, including one-way ANOVA or two-tailed paired t-tests, were performed with Bonferroni's correction where appropriate. The level of signi cance was set atp< 0.05. 3. Results 3.1. Power The two age groups showed signi cant differences in the peak power output rel- ative to body mass at baseline (younger: 5.24 0.58 W/kg, older: 4.66 0.43 W/kg (p= 0.01)(Table) . Considering peak power output relative to FFM, there were no sig- ni cant differences between the age groups (younger: 5.79 0.47 W/kgFFM, older: 5.60 0.71 W/kgFFM (p= 0.44)). Table peak power output (PP), average power output (AP), and percentage of fatigue during the different WAnT protocols for the younger and older groups. In PP, signi cant differences were found between WAnTs one and WAnTs four for both groups in the one-, three-, and ten-minute recovery protocols. AP also declined signi cantly between WAnTs one and four in both groups throughout the one- and three-minute protocols. In the ten-minute protocol, AP decreased signi cantly in the younger group only. Fatigue (%) decreased signi cantly from WAnTs one to four in the HIIT protocol with one minute recovery in the older group and in the ten-minute recovery protocol in the younger groups. The three-minute recov-

group only. Fatigue (%) decreased signi cantly from WAnTs one to four in the HIIT protocol with one minute recovery in the older group and in the ten-minute recovery protocol in the younger groups. The three-minute recov-

The study examines recovery differences in younger and older athletes during HIIT.