Early Adaptations to a Two-Week Uphill Run Sprint Interval Training and Cycle Sprint Interval Training

This study sought to compare early physiological and performance adaptations between a two-week cycle sprint interval training (SIT) and uphill run sprint training (UST) programs. Seventeen recreationally active adult males (age = 28 5 years; body mass (BM) = 78 9 kg) were assigned to either a control (n= 5), SIT (n= 6), or UST (n= 6) group. A discrete group of participants (n= 6, age = 33 6 years, and body mass = 80 9 kg) completed both training protocols to determine acute physiological responses. Intervention groups completed either a run or cycle peak oxygen uptake (VO2peak) test (intervention type dependent) prior to and following two weeks of training. Training comprised of three sessions per week of 4 30-s “all-out” sprints with a four-minute active recovery between bouts on a cycle ergometer against 7.5% of body mass in the SIT group and on a 10% slope in the UST group. The VO2peak values remained unchanged in both training groups, but time-to-exhaustion (TTE) was signi cantly increased only in the UST group (pre—495 40 s , post—551 15 s;p= 0.014) and not in the SIT group (pre—613 130 s, post—634 118 s ,p= 0.07). Ventilatory threshold (VT) was signi cantly increased in both training groups (SIT group:pre—1.94 0.45 L min 1 , post—2.23 0.42 L min 1 ;p< 0.005, UST group: pre—2.04 0.40 L min 1 , post—2.33 0.34 L min 1 ,p< 0.005). These results indicate that UST may be an effective alternative to SIT in healthy individuals. Keywords:high-intensity interval training; training adaptations; lactate; ventilator threshold 1.

signi cantly increased in both training groups (SIT group:pre—1.94 0.45 L min 1 , post—2.23 0.42 L min 1 ;p< 0.005, UST group: pre—2.04 0.40 L min 1 , post—2.33 0.34 L min 1 ,p< 0.005). These results indicate that UST may be an effective alternative to SIT in healthy individuals. Keywords:high-intensity interval training; training adaptations; lactate; ventilator threshold 1. Introduction Cycle sprint interval training (SIT) consisting of repeated brief “all-out” cycle sprints interspersed with recovery periods offers a time-ef cient alternative to traditional endurance training [1]. A commonly studied SIT protocol involves 30-s Wingate tests against 7.5% of body mass repeated four to six times separated by 4 min of recovery [2]. For example, six sessions of SIT performed over two weeks have been shown to improve skeletal muscle oxidative metabolism and cycling time to exhaustion in recreationally active individuals [3]. Seven weeks of progressive SIT in healthy men signi cantly increased glycolytic and oxidative muscle enzyme activity, maximum short-term power output, and maximal oxygen uptake (VO2max) [4]. Similarly, aerobic and anaerobic adaptations as demonstrated by improvements in a 5-km cycling time trial, VO2max, peak, and average power output have been found after two weeks of SIT in healthy, young adults [5]. Although SIT offers a low-volume training paradigm with signi cant health and performance bene ts, previous studies mainly used specialized cycle ergometers to control the intensity of the exercise [3–6]. While cycle ergometers are accurate, they are not always ecologically valid and may be relatively costly to acquire. The uphill sprint training (UST), which is also called running SIT, may offer Sports2018,6, 72; doi:10.3390/sports6030072

Sports2018,6, 72 2 of 13 a viable option in the training prescription “menu” to elicit training adaptations in a short time frame without needing access to any specialized equipment. However, it may not always be possible to complete the UST outdoor where weather and/or a suitable incline cannot be controlled. Since there are both advantages and disadvantages to these training approaches, it would be of use to understand to what extent these approaches can be used interchangeably to allow practitioners the scope to select the most appropriate training approach for their need. Previous research has demonstrated that UST is an effective training modality in a range of exercise programs and athletic activities. For example, eight weeks of UST has been shown to increaseVO2max and insulin sensitivity and reduce plasma low density lipoprotein-cholesterol in healthy young participants [7]. Similarly, a more recent study by Willoughby et al. [8] found that four weeks of UST improves cardiorespiratory and anaerobic tness in young and middle-aged adults. In addition, the ef cacy of UST has been demonstrated in athletic populations including the semi-professional male soccer players [9], semi-professional female eld hockey players [10], and well-trained distance runners [11]. While both sprinting protocols appear to lead to similar improvements in cardiorespiratory tness in non-athletic populations (cycling—6.2–7.8% [12,13], running—3.9–11.5% [9,10], no studies have directly measured early physiological responses between SIT and UST in healthy, recreationally-trained male adults. Therefore, the primary aim of this study was to compare early physiological and performance adaptations, which is represented by peak oxygen uptake (VO2peak), time-to-exhaustion (TTE), and the ventilatory threshold (VT) following six sessions of SIT and UST performed over two weeks. The secondary aim was to determine acute physiological responses following both protocols to help understand mechanisms underpinning the training adaptations. We hypothesized that six sessions of UST would lead to similar early physiological adaptations compared to SIT. 2. Materials and Methods 2.1. Participants Seventeen healthy, recreationally active men (minimum 3 sessions per week of 45 min with moderate intensity exercise) participated in the training study. Participants were randomly allocated to a control group (CG), sprint interval training (SIT)

training adaptations. We hypothesized that six sessions of UST would lead to similar early physiological adaptations compared to SIT. 2. Materials and Methods 2.1. Participants Seventeen healthy, recreationally active men (minimum 3 sessions per week of 45 min with moderate intensity exercise) participated in the training study. Participants were randomly allocated to a control group (CG), sprint interval training (SIT) group, or an uphill sprint training (UST) group. A discrete group (DG) of 6 participants completed both training protocols to determine acute physiological responses. The characteristics of the participants are presented in Table. All groups were asked to continue with their regular daily activities and training programs throughout the study period. Participants were also asked to refrain from any vigorous exercise 24 h before each test. The participants were informed of the experimental protocol both verbally and in writing before giving informed consent. The study protocol was approved by the Abertay University Ethics Committee and conducted in accordance with the Declaration of Helsinki. Table 1.Characteristics of all participants (mean standard deviation). Characteristic CG (n= 5) SIT (n= 6) UST (n= 6) DG (n= 6) Age (years) 27 4 32 7 25 5 33 6 Body Mass (kg) 77 9 74 8 84 9 80 9 BMI (kg m 2 ) 25 4 23 2 26 3 25 3 2.2. Procedures 2.2.1. Baseline Testing After reporting to the Human Performance Laboratory, the UST group completed only the run VO2peak test and the SIT group completed only the cycle VO2peak test. The control group completed both run and cycle VO2peak tests in a randomized fashion separated by a minimum of 48 h.

Sports2018,6, 72 3 of 13 2.2.2. Run VO2Peak Participants performed an incremental treadmill test to volitional exhaustion on a motorized treadmill (H/P/Cosmos Mercury, Nussdorf-Traunstein, Germany) to determine VO2peak via breath by breath analysis (Metalyzer ® 3B gas analyzer, Cortex, Leipzig, Germany), which was described by Harling et al. [14]. In addition, time-to-exhaustion (TTE) was recorded using a Quantum 5500 stop clock (EA Combs Ltd., London, UK). Participants performed a standardized warm-up on a treadmill for 5 min at 7.5 km h 1 . The incremental test then began at 10 km h 1 with the speed increased by 1 km h 1 every minute until volitional exhaustion. At the end of the test, participants walked on the treadmill for 5 min at 5 km h 1 at a 0% inclination. The VO2peak calculated as the highest oxygen consumed over a 30-s period and ventilatory threshold was calculated using the V-slope method [15]. 2.2.3. Cycle VO2Peak Participants performed an incremental cycling test to volitional exhaustion to determine the VO2peak using breath by breath analysis (Metalyzer ® 3B gas analyzer, Cortex, Leipzig, Germany). The test was designed to produce a similar time to exhaustion as the run VO2peak test described above. The TTE was recorded using a Quantum 5500 stop clock (EA Combs Ltd., London, UK). The participants performed a 5 min warm up cycling at 60 W (Monark 894E Peak bike, Monark Exercise AB, Vansbro, Sweden). The test then began with the participant cycling at 60 W for 1 min and the intensity increased by 25 W every minute until volitional exhaustion or the participant could not maintain a cadence of 60 r min 1 . During the test, participants could pedal faster than 60 r min 1 . At the end of the test, participants cycled for 5 min at 30 W. The VO2peak calculated as the highest oxygen consumed over a 30-s period and the ventilatory threshold was calculated using the V-slope method [15]. Both VO2peak tests were repeated after two weeks for the control group and three days after the completion of training for the intervention groups. All

end of the test, participants cycled for 5 min at 30 W. The VO2peak calculated as the highest oxygen consumed over a 30-s period and the ventilatory threshold was calculated using the V-slope method [15]. Both VO2peak tests were repeated after two weeks for the control group and three days after the completion of training for the intervention groups. All tests were performed within 2 h of the same time of the day. 2.2.4. Sprint Interval Training Protocol The SIT protocol was similar to the protocol used previously [16]. Six sprint interval sessions were spread over 14 days with a minimum of 24 h of rest between sessions. Each training session consisted of 4 30-s “all-out” cycling efforts against 7.5% of body mass with 4 min of active recovery between sprints (1:8 work-to-rest ratio). Resistance was automatically applied to the cycle ergometer (Monark 894E Peak bike, Monark Exercise AB, Sweden) once the participant was cycling at 110 r min 1 , which initiated the start of the 30-s cycle sprint. During recovery, participants remained on the bike and cycled at a low cadence (<50 r min 1 ) without resistance. Peak and average power output was automatically calculated for each sprint in the six training sessions using the Monark Anaerobic Test Software version 2.24.2 (Monark Exercise AB, Vansbro, Sweden). 2.2.5. Uphill Sprint Training Protocol The UST protocol consisted of six uphill sprint sessions spread over 14 days with a minimum of 24 h of rest between sessions. Similar to previous studies [11,17], each training session consisted of 4 30-s“all-out” uphill sprint efforts on a 10% slope. During a 4-minute recovery, subjects walked back down the hill to the starting position. Average power output during the uphill sprint was calculated using the following equations as described by di Prampero [18]. Work = Potential Energy = m g d sin where m is the participants mass in kg, g is the force of gravity, d is the distance covered in 30 s, and is the angle of the hill. Power = W/t where W is the work done and t is the

the following equations as described by di Prampero [18]. Work = Potential Energy = m g d sin where m is the participants mass in kg, g is the force of gravity, d is the distance covered in 30 s, and is the angle of the hill. Power = W/t where W is the work done and t is the time duration of the sprint.

Sports2018,6, 72 4 of 13 2.2.6. Acute Responses to both Training Protocols Six participants from the discrete group performed 2 30-s “all-out” efforts using both sprint interval and uphill sprint training protocols in a randomized order on different days separated by at least 24 h. Heart rate (Polar Electro, Kempele, Finland), VO2, and VCO2(MetaMax ® 3B gas analyser, Cortex, Leipzig, Germany) were recorded continuously throughout the sprint and each 4 min recovery period averaged over 5 s. 2.2.7. Lactate Measurement Fingertip blood samples were taken immediately upon completion of each sprint and compared to a sample taken prior to the training session to analyze blood lactate concentration. The skin was punctured using an Accu-check single use lancet (Roche Diagnostics, Burgess Hill, UK) and pressure applied to the nger to draw the capillary blood. The initial drop was discarded and the second drop was taken for lactate analysis using the Lactate Pro blood lactate meter (Arkray Inc., Kyoto, Japan). A cotton pad was placed on the incision and pressure applied until bleeding had stopped. 2.3. Statistical Analysis Data are expressed as a mean standard deviation. Area under the curve for heart rate (HR), VO2, and VCO2was calculated using the standard trapezoid rule [19]. The Shapiro-Wilk test was used to determine whether data were normally distributed and a paired samplet-test was used to compare the acute and training effect within a group. An unpairedt-test was used to compare between groups [7]. The null hypothesis was rejected at the 5% level (p< 0.05). Effect size between the groups was calculated using the method of Morris and DeShon for repeated measure design to allow for the correction for different sample sizes and pre-test values [20]. The effect size for the acute response was calculated as Cohen'sd, which allows for measuring the difference between the groups in terms of their common standard deviation. For both, the effect size was de ned as follows:d< 0.2 trivial effect, 0.2–0.5 small effect, 0.6–1.1 moderate effect, and 1.2–1.9 as a large effect [21]. 3. Results 3.1. Training Results 3.1.1. VO2Peak At baseline, the VO2peak was similar between training groups

as Cohen'sd, which allows for measuring the difference between the groups in terms of their common standard deviation. For both, the effect size was de ned as follows:d< 0.2 trivial effect, 0.2–0.5 small effect, 0.6–1.1 moderate effect, and 1.2–1.9 as a large effect [21]. 3. Results 3.1. Training Results 3.1.1. VO2Peak At baseline, the VO2peak was similar between training groups (SIT: 49 7 mL kg 1 min 1 , UST: 48 4 mL kg 1 min 1 ,p> 0.05) and did not signi cantly change in both groups called SIT (pre: 49 7 mL kg 1 min 1 , post: 49 7 mL kg 1 min 1 ,p> 0.05) and UST (pre: 48 4 mL kg 1 min 1 , post: 50 6 mL kg 1 min 1 ,p> 0.05) after two weeks of training. However, there was a small effect size between groups with a greater change in UST (d= 0.34). 3.1.2. Time-to-Exhaustion There was no signi cant difference in the TTE for the cycling and running protocols in the control group (running TTE: 426 71 s, cycling TTE: 515 102 s,p> 0.05). There were also no signi cant changes in the TTE during the cycling and running protocols in the control group after two weeks (running TTE: 426 71 s vs. 441 94 s,p> 0.05, cycling TTE: 515 102 s vs. 537 101 s,p> 0.05). At baseline, TTE was similar between training groups (SIT: 613 135 s, UST: 495 40 s,p> 0.05, Figure). Following 2 weeks of training, the TTE had increased by ~3% in the SIT group and ~11% in the UST group (SIT: 613 135 s vs. 634 118 s,p= 0.07, UST: 495 40 s vs. 551 15 s,p= 0.014, Figure). The magnitude of the change in TTE was signi cantly different between the training groups (SIT: 3 5%, UST: 11 9%,p= 0.04). There was a small effect size between training groups with a greater change in UST (d= 0.34) and a large effect size between the control group and the UST group (d= 0.71).

in TTE was signi cantly different between the training groups (SIT: 3 5%, UST: 11 9%,p= 0.04). There was a small effect size between training groups with a greater change in UST (d= 0.34) and a large effect size between the control group and the UST group (d= 0.71).

Sports2018,6, 72 5 of 131 ** Figure 1. Absolute percentage and individual changes in time-to-exhaustion in SIT and UST groups. (A) Absolute changes pre-SIT and post-SIT and UST, *p< 0.05 pre-compared to post; (B) Percentage change from the baseline in SIT and UST groups, **p< 0.05 SIT compared to UST; (C) Individual changes in time-to-exhaustion pre-SIT and post-SIT and UST.

Sports2018,6, 72 6 of 13 3.1.3. Ventilatory Threshold At baseline, there was no signi cant difference in the VT for either of the training group (SIT:1.94 0.45 L min 1 , UST: 2.04 0.40 L min 1 ,p> 0.05, Figure). In both training groups, the VT was signi cantly increased after two weeks of training (SIT: pre—1.94 0.45 L min 1 , post—2.23 0.42 L min 1 ,p< 0.005; UST: pre—2.04 0.40 L min 1 , post—2.33 0.34 L min 1 , p< 0.005; Figure). There was no signi cant difference in the magnitude of change between groups (SIT: 16 11%, UST: 15 6%;p> 0.05).1 * * Figure 2. Absolute and individual changes in the ventilatory threshold in SIT and UST groups, (A) Ventilatorythreshold pre-SIT and post-SIT and UST, *p< 0.05 pre compared to post; (B) Individual changes in ventilatory threshold pre-SIT and post-SIT and UST. 3.1.4. Average Power In both groups, the average power produced was similar across all sessions (Table). The power drop between sprint 1 and 4 was signi cantly altered after UST but not SIT (UST session 1: 26 4%,

The study compares adaptations from two training methods over two weeks.