Training volume is an important variable in the prediction of running performance (36). However, a sudden increase in running volume, particularly with an absolute volume above 40 miles per week, is one of the strongest independent risk factors associated with running injuries (20). Seventy percent of runners at different performance levels are reported to sustain overuse injuries yearly (26). Therefore, reducing weekly running volume may help prevent the risk of injury among runners by decreasing the training impact load. However, this cannot be done at the expense of losing important physiological adaptations. Maximal oxygen uptake (V[Combining Dot Above]O2max), lactate threshold (LT), and running economy are the main physiological determinants of long-distance running performance (36). It has also been suggested that anaerobic capacity and skeletal muscle power may influence endurance performance (7,38). Therefore, introducing other forms of training that target these components may improve running performance and help reduce orthopaedic injuries (18,19,37). Furthermore, cross-training has been found to be an effective method to maintain training adaptations in runners during recovery following injury (39).
Recent findings demonstrate that high-intensity interval training (HIT) offers a time-efficient training method for sport performance by inducing similar skeletal muscle and cardiovascular adaptations when compared with traditional endurance training (1,9,22,25). Two weeks of HIT has been shown to increase skeletal muscle lactate and H+ transport capacity (40), increase aerobic and anaerobic enzyme activity (41), and improve muscle oxidative capacity and mitochondrial content (9,10). These adaptations have also been shown to result in functional improvements in moderately trained male triathletes as reflected by increased cyclingV[Combining Dot Above]O2peak, cycling time to exhaustion, and reduced self-paced cycling and running time-trials (TTs) (17,27).
Although the HIT protocol seems to induce endurance adaptation, the most effective method remains unclear given that the work-to-rest ratios used by the aforementioned studies (1,9,22,25) varied substantially. For example, Hazell et al. (25) used 3 experimental groups with unmatched training load with work-to-rest ratios of 1:8, 1:12, and 1:24 over 2 weeks. Therefore, an ideal work-to-rest stimulus for HIT is still unknown. More recently, a study by Edge et al. (16) demonstrated no significant effect on muscle or endurance performance adaptations between the 2 intense interval training protocols of matched training volume and intensity but different rest periods (i.e., 1 vs. 3 minutes). However, they used 2-minute HIT bouts and it is unclear if manipulation of the rest period would lead to the same results during shorter supramaximal HIT exercise bouts.
Therefore, the primary aim of the present study was to determine whether 6 sessions of high-intensity cycling training involving 6 × 10-second sprints over 2 weeks is an effective method to improve running performance measures. A secondary aim was to measure the magnitude of performance change in 3 different work-to-rest groups. It was hypothesized that the HIT would improve running performance without increasing running mileage and that the group using the shortest work-to-rest period would demonstrate the greatest change in physiological and performance outcomes.
Experimental Approach to the Problem
A 4-group pre-post research test design was used in the study. To assess responses to cycling HIT, the subjects were tested pretraining and posttraining, with testing being performed over a 7-day period and within 48 hours after completing training. Testing included body height and mass assessment and 3-km self-paced running TT (day 1), V[Combining Dot Above]O2peak determination and time-to-exhaustion (day 2) and 30-second Wingate anaerobic test (WAnT) (day 3). Subsequently, subjects were randomized using stratified sampling based on their baseline V[Combining Dot Above]O2peak into 1 of the 3 HIT groups or a control group. Over the next 2 weeks, all training groups underwent 6 sessions of 6 × 10-second “all-out” cycling efforts against a resistance equalling 7.5% of body weight with different recovery periods (R30 group, 30-second rest; R80 group, 80-second rest; and R120 group, 120-second rest). The remaining group acted as a control (CON) group which completed pretest and posttest 2 weeks apart while maintaining their normal training regime but did not complete HIT protocol. Posttraining tests were performed in the identical order. Furthermore, for a given subject, each training and testing protocol was performed within 2 hours of the same time of the day. The subjects were also asked to refrain from vigorous training for 24 hours before each test and to maintain their normal training and diet routine throughout the study period.
Twenty-four competitive runners (10 male participants and 14 female participants, age range 25–65 years) from local running clubs volunteered to participate in this study. At the time of the study, all subjects ran for at least 25 miles per week. In addition, 8 subjects (4 male participants and 4 female participants) served as controls. Physical characteristics of the subjects are shown in Table 1, with no statistical difference between groups for performance measures. Subjects were also familiar with exhaustive treadmill running and could complete 3 km in less than 18 minutes. All provided written informed consent and completed a Physical Activity Readiness Questionnaire (PAR-Q) before participation in the procedures that were approved by the University Research Ethics Committee.
Subjects were required to report to the Human Performance Laboratory for performance tests on 3 separate days with at least 24 hours between each testing session over the course of 1 week. During the initial visit, the height and mass of each subject were measured to the nearest 0.1 cm (SECA 216 Mechanical Stadiometer; SECA, Hamburg, Germany) and 0.1 kg (SECA 796 Column Scale; SECA), respectively.
Participants performed a 3-km self-paced running TT on a treadmill (H/P/Cosmos Mercury, Germany) set at 1% gradient (30) and were given instructions to complete the test in the fastest possible time. A coefficient of variation of the 3-km running TT on an outdoor 400-m track has been reported to be 1.2% (29). Before the TT, the participants did a 5-minute standardized warm-up, which consisted of running for 3 minutes at a constant speed (7.5 km·h−1 for women and 9.1. km·h−1 for men) and 2 minutes of prerace stretching routine. After setting initial speed at 11.2 and 12.9 km·h−1 for women and men, respectively, participants were free to manually control their own speed and were able to adjust it constantly throughout the TT. However, there was no visual feedback apart from distance covered to ensure that subsequent trials are not affected by a pacing strategy (3). Standardized verbal encouragement for each participant was provided throughout the test.
Assessment of V[Combining Dot Above]O2peak
Participants performed a continuous graded exercise test on a motorized treadmill (H/P/Cosmos Mercury 4.0; Cosmos, Nussdorf-Traunstein, Germany) to determineV[Combining Dot Above]O2peak through breath-by-breath gas collection system (Metalyzer3B gas analyser; Cortex, Leipzig, Germany). In addition, time-to-exhaustion was recorded using a Quantum 5500 stop clock (EA Combs Ltd., London, United Kingdom), and subjects were not allowed to see the time throughout the test. Briefly, following a 5-minute standardized warm-up, which consisted of running at a constant speed (9.6 km·h−1 for women and 11.2 km·h−1 for men) at 0% gradient, the speed was increased (11.2 and 12.9 km·h−1 for women and men, respectively). After 2 minutes, the gradient was increased by 2.5% and then every 2 minutes until volitional exhaustion (44). V[Combining Dot Above]O2peak was taken as the highest value averaged over 30-second collection periods.
Anaerobic Power Test
Anaerobic power output was assessed by a 30-second WAnT using a Monark Ergomedic 894E cycle ergometer (Monark Exercise AB, Varberg, Sweden) against a resistance equalling 7.5% of body weight. After the ergometer seat height had been adjusted, participants performed a 3-minute warm-up cycling at 60 W, and subjects were instructed to perform a 30-second “all-out” sprint pedalling as fast as possible from the start with a predetermined resistance automatically applied to the flywheel upon reaching 100 r·min−1. Verbal encouragement was provided throughout the test. Relative values of peak power (the highest power output over any 5-second reached during the test) and mean power (over the entire test) were automatically calculated by computer (Monark Anaerobic Test Software version 2.24.2; Monark Exercise AB). In addition, blood lactate concentration was determined from a fingertip capillary blood sample (Lactate Pro; Arkay, Inc., Kyoto, Japan) at rest, immediately after the test, 2 and 5 minutes posttest. Briefly, the skin was punctured using an Accu-check single-use lancet (Roche Diagnostics, West Sussex, United Kingdom) and pressure applied to the finger to draw the blood. The initial drop was discarded and the second drop was taken for lactate analysis.
At least 48 hours after the last baseline test, subjects completed their first session of HIT consisting of 6 × 10-second “all-out” cycling efforts against a resistance equalling 7.5% of body weight. Rest periods were prescribed based on the relevant groups (i.e., R30, R80, and R120) with active recovery in the form of unloaded pedalling at 60 r·min−1 completed in between intervals. Subjects were weighed in before each session to ensure that accurate resistance on the flywheel was used throughout the duration of the training programme. The same training routine was repeated 5 more times over the next 2 weeks with at least 24 hours between the sessions. Heart rate (HR) (Polar Electro, Kempele, Finland) and peak power output (PPO) and mean power output (MPO) (Monark Anaerobic Test Software version 2.24.2; Monark Exercise AB) were recorded continuously throughout. All subjects were verbally encouraged during training.
All subjects in the training groups repeated 3-km time-trail, V[Combining Dot Above]O2peak, and WAnT in the same order within 48 hours after completing training. Subjects in the control group were retested 2 weeks after the completion of baseline testing.
All performance data were normalized to baseline to determine the magnitude of change before statistical analysis. Data were checked for skewness and kurtosis, and these values did not exceed twice the standard error; therefore, the data were deemed to be normally distributed. A 1-way analysis of variance with Student-Newman-Keuls post hoc testing was used to compare the magnitude of change between groups and to analyze the average training HR response. A paired samples t-test was used to compare the preoutcome and postoutcome in the control group. The null hypothesis was rejected at the 5% level (p ≤ 0.05). The Cohen's d effect size was calculated to quantify the magnitude of difference between groups, with effect size defined as trivial (0.0–0.2), small (0.2–0.5), moderate (0.6–1.1), and large (1.2–1.9) (11).
At baseline, time to complete 3 km was not significantly different between groups (R30 group: 889 ± 83 seconds; R80 group: 858 ± 113 seconds; R120 group: 875 ± 71 seconds; control group: 814 ± 126 seconds; p > 0.05 for all group comparisons) and the control group was unchanged after 2 weeks (pre: 814 ± 126 seconds; post: 813 ± 114 seconds; p = 0.7). Two weeks of HIT training resulted in a significant decrease in 3-km TT in the R30 group (3.1 ± 4.0%, p = 0.04, compared with control, d = 0.9; Figure 1) but a nonsignificant change in the R80 group (2.4 ± 2.7%, p = 0.1, compared with control, d = 0.9; Figure 1) and R120 group (2.4 ± 2.4%, p = 0.1, compared with control, d = 0.9; Figure 1). There was no significant difference in the magnitude of change between the HIT groups (R30 vs. R80, p = 0.6, d = 0.2; R30 vs. R120, p = 0.6, d = 0.2; R80 vs. R120, p = 1.0, d = 0.0).
Time to Exhaustion
At baseline, time to exhaustion was not significantly different between groups (R30 group: 703 ± 76 seconds; R80 group: 709 ± 84 seconds; R120 group: 692 ± 68 seconds; control group: 755 ± 89 seconds; p > 0.05 for all group comparisons; Figure 1), and the control group was unchanged after 2 weeks (pre: 755 ± 89 seconds; post: 750 ± 97 seconds; p = 0.5). Following 2 weeks of HIT training, time to exhaustion significantly improved in the R30 group (6.4 ± 6.3%, p = 0.003, compared with control, d = 1.4; Figure 1) and the R80 group (4.4 ± 2.7%, p = 0.03, compared with control, d = 1.6; Figure 1), but there was no significant increase in the R120 group (1.9 ± 5.0%, p = 0.2, compared with control, d = 0.6; Figure 1). There was a significant difference in the magnitude of change between the R30 and R120 groups (p = 0.05, d = 0.8) but not between the R30 and R80 groups (p = 0.4, d = 0.4) or the R80 and R120 groups (p = 0.3, d = 0.6).
V[Combining Dot Above]O2peak
At baseline, V[Combining Dot Above]O2peak was not significantly different between groups (R30 group: 45.1 ± 8.4 ml·kg−1·min−1; R80 group: 43.3 ± 3.9 ml·kg−1·min−1; R120 group: 43.6 ± 7.2 ml·kg−1·min−1; control group: 46.6 ± 6.2 ml·kg−1·min−1; p > 0.05 for all group comparisons; Figure 1) and the control group was unchanged after 2 weeks (pre: 46.6 ± 6.2 ml·kg−1·min−1; post: 46.9 ± 6.3 ml·kg−1·min−1; p = 0.8). Two weeks of HIT training did not increaseV[Combining Dot Above]O2peak significantly in any of the groups (R30 group: 6.9 ± 14%, p = 0.2, compared with control, d = 0.5; R80 group: 4.7 ± 6.4%, p = 0.4, compared with control, d = 0.6; R120 group: 0.3 ± 4.4%, p = 0.8, compared with control, d = 0.2; Figure 1). There was no significant difference in the magnitude of change between groups (R30 vs. R80, p = 0.6, d = 0.2; R30 vs. R120, p = 0.1, d = 0.7; R80 vs. R120, p = 0.3, d = 0.9).
At baseline, peak and average power was significantly different between R80 and R120 (p > 0.05) groups but not between other groups (Figure 2) and the control group was unchanged after 2 weeks (peak power—pre: 11.3 ± 2.5 W·kg−1; post: 11.4 ± 2.4 W·kg−1; p = 0.9; average power—pre: 7.5 ± 0.8 W·kg−1; post: 7.5 ± 0.9 W·kg−1; p = 0.7). Following 2 weeks of HIT training, there was no significant change in average power in the R30 group (0.3 ± 4.1%, p = 0.8 compared with control, d = 0.2; Figure 2) but significant increases in the R80 group (4.6 ± 4.2%, p = 0.03, compared with control, d = 1.4; Figure 2) and the R120 group (5.3 ± 5.9%, p = 0.02, compared with control, d = 1.2; Figure 2). There was a significant difference in the magnitude of change between the R30 and R80 groups (p = 0.05, d = 1.0) and the R30 and R120 groups (p = 0.03, d = 1.0) but not the R80 and R120 groups (p = 0.7, d = 0.1). Peak power was not increased significantly in the R30 group (4.3 ± 6.1%, p = 0.3, compared with control, d = 0.6; Figure 2) or the R120 group (7.1 ± 7.9%, p = 0.09, compared with control, d = 0.9; Figure 2) but there was a significant increase in the R80 group (8.5 ± 8.2%, p = 0.04, compared with control, d = 1.1; Figure 2). There was no significant difference in the magnitude of change between the groups (R30 vs. R80, p = 0.2, d = 0.6; R30 vs. R120, p = 0.4, d = 0.4; R80 vs. R120, p = 0.7, d = 0.2).
Blood lactate concentrations after the Wingate were not changed following 2 weeks of HIT, regardless of recovery duration (Table 2).
Average Heart Rate During Training
Average HR was significantly greater in the R30 group compared with the R120 group for all training sessions (p = 0.000; Figure 3) and was significantly greater in the R80 group compared with the R120 group for training sessions 1 and 2 (p = 0.004; Figure 3). There was no significant difference between R30 and R80 for average training HR but there was a trend for it to be greater in the R30 group (p = 0.268; Figure 3).
The purpose of this study was to measure the magnitude of changes of running performance and aerobic capacity (as determined byV[Combining Dot Above]O2peak) following a matched-work cycling HIT protocol with different rest periods. In accordance with our hypothesis, the main finding was that a short cycling HIT protocol, especially with lower work-to-rest ratio, provides sufficient training stimulus to have a carryover effect into running performance (Figure 1). These findings demonstrate that a nonspecific training may contribute to improved running performance in already trained runners. Recent studies using cycling HIT have reported varying degrees of health and performance benefits (17,22,33). Although the mechanisms contributing to HIT adaptation is dependent on the training statuses of individuals, performance improvement following cycling HIT has been attributed to alterations in central (i.e., cardiovascular) and peripheral (i.e., skeletal muscle) adaptations (22,33). However, the extent of performance improvements and related physiological changes elicited by cycling HIT seems to depend on the duration and intensity of each bout, number of intervals completed, and the type and duration of recovery used (32,42). The major findings of this study support the notion that manipulation of rest duration during a matched-work cycling HIT protocol results in different adaptations for long-distance runners.
Following 6 sessions of HIT over 2 weeks, the R30 group significantly (p ≤ 0.05) improved the 3-km TT performance, but there was no significant improvement in the R80 and R120 groups (p > 0.05) (Figure 1). The magnitude of change was not significantly different between the HIT groups (p > 0.05), with only a small effect size reported for the R30 group compared with the R80 (d = 0.2) and R120 (d = 0.2) groups (Figure 1). The R30 group had the greatest (3.1%) reduction in time taken to complete the TT compared with R80 (2.4%) and R120 (2.4%) groups, and the magnitude of change is similar to that reported previously for a 5-km cycling TT (3–5.2%) (25). Even greater improvements were found by Jakeman et al. (27) who demonstrated that 6 training sessions using 10 × 6-second Wingate-based sprints resulted in a 10% decrease in self-paced 10-km cycling TT in subelite triathletes. Similarly, Burgomaster et al. (8,10) observed a 9.6% decrease in a 250-kJ self-paced TT (approximately 10 km) and a 4% decrease in a 50-kJ self-paced TT (approximately 2 km) in young active men after 6 sessions of 4–6 × 30-second cycling sprints. This suggests that despite different HIT volumes (duration × number of sprints) used in the above studies, the magnitude of performance improvements can be expected to be greater during a longer TT. It was suggested by Sloth et al. (43) that aerobic gains may depend on the work-to-rest ratios used during HIT protocols. This may explain why the magnitude of change was greatest in the R30 group (Figure 1). Shorter recovery times between repeated high-intensity cycling sprints increase aerobic metabolism demand in subsequent sprints (21), mainly because of reduced muscle phosphocreatine (PCr) availability (4). Although we did not measure oxygen uptake (V[Combining Dot Above]O2) during recovery periods directly, average HR data from training sessions were significantly greater in the R30 group compared with the R120 group in all training sessions (p = 0.000) and in the R80 group compared with the R120 group (p = 0.004) during the first 2 training sessions (Figure 3). This indicates that the overall cardiovascular demand of a training session was higher with shorter recovery, suggesting a greater aerobic demand. In other studies that have measured HR during a repeated sprint session, shorter work-to-rest periods produce a greater cardiovascular demand (6,35). Likewise, levels of oxygen uptake during and following sprints are greater with shorter work-to-rest ratios (24).
Time-trial is a more ecologically valid test to measure endurance performance, whereas time to exhaustion is a test of exercise capacity (14). Only R30 and R80 groups significantly improved their time to exhaustion (p ≤ 0.05), with no significant improvement in the R120 group (p > 0.05) (Figure 1). The magnitude of change was dependent on recovery duration as lower work-to-rest ratios (R30 +6.4%, d = 0.8; and R80 +4.4%, d = 0.6) had a greater effect on time to exhaustion compared with a higher work-to-rest ratio (R120 +1.9%). In 1 study (10), recreationally active subjects doubled their endurance time to fatigue following 2 weeks of HIT during cycling exercise at ∼80%V[Combining Dot Above]O2 peak. In contrast, Jakeman et al. (27) reported a nonsignificant change during an incremental ramp cycling test to volitional exhaustion after 2 weeks of cycling HIT. One of the underlying mechanisms responsible for a better exercise tolerance observed in 2 groups (i.e., R30 and R80) with less rest time may be a greater improvement in skeletal muscle oxidative capacity. Alterations in mitochondrial activity are reported after 2 weeks of cycling HIT (9) and a rightward shift in the blood lactate curve (27) seen with a 1:8 and 1:10 work-to-rest ratio, respectively. These muscle adaptations are important in explaining the improvement in endurance performance that occurs with training, and the longer recovery may not provide a large enough stimulus to promote sustained changes in these systems. Others have suggested that improvements in time to exhaustion are related to a smaller O2 deficit at the start of the exercise, resulting in a smaller anaerobic contribution (15). However, based on the results of this study, it is impossible to determine whether central or peripheral physiological mechanisms are affecting the improvement in running time to exhaustion after cycling HIT training with short recovery periods.
Despite significant changes in TT in the R30 group and time to exhaustion in groups R30 and R80, there were no significant changes inV[Combining Dot Above]O2peak in any of the training groups (p > 0.05) (Figure 1). Although the magnitude of change between groups was nonsignificant (p > 0.05), the R30 (+6.9%, d = 0.7) and R80 (+4.7%, d = 0.9) groups showed a trend for greater adaptations compared with the R120 group (−0.3%). The magnitude of change in V[Combining Dot Above]O2peak in the R30 and R80 groups is similar to that which has been reported previously for 30-second sprint protocols over 2 weeks (1). Therefore, an increase in the length of sprint may not result in greater adaptations of V[Combining Dot Above]O2peak. Hazell et al. (25) also reported a smaller adaption inV[Combining Dot Above]O2peak with a 1:12 work-to-rest ratio compared with a 1:8 work-to-rest ratio. This shows that the shorter recovery period places a greater demand on the body leading to greater adaptations in aerobic capacity. Together with the HR data (Figure 3), these findings suggest that cardiovascular training intensity may be important in regulating training response of V[Combining Dot Above]O2peak.
Peak power output was significantly increased only in the R80 (p ≤ 0.05) but not in the R30 and R120 groups (p > 0.05) (Figure 2). The R80 showed the greatest change in PPO (+8.5%) in comparison with the R30 and R120 groups (+4.3%, d = 0.6 and +7.1%, d = 0.2, respectively). Mean power output was significantly higher in the R80 and R120 groups (p ≤ 0.05) but not in the R30 group (p > 0.05) (Figure 2). The magnitude of change in MPO was highest in the R120 group (+5.3%) compared with the R30 group (0.3%, d = 1.0) and the R80 group (4.6%, d = 0.1). The magnitude of improvements is similar to that reported previously for 10-second sprints and 1:8 work-to-rest ratio (1,25). The HIT has been shown to upregulate a number of glycolytic enzymes (31,34) and result in significant increases in PCr and glycogen concentrations after training (41). Two minutes of recovery after the 10-second cycling sprint has been demonstrated to be long enough for subjects to reproduce peak but not mean power in a subsequent sprint (5,25). Therefore, lower than 1:8 ratio seem to have a negative effect on anaerobic adaptations because of the subsequent sprints relying more heavily on aerobic metabolism. Positive changes in power production following HIT may also occur because of the neuromuscular changes, such as increased motor unit recruitment, firing rate, and synchronization (13). However, shorter recovery periods between sprint bouts may induce greater fatigue, thereby limiting neural stimuli for optimal power development. The extent of blood lactate accumulation after the Wingate test was the same for each group before and after 2 weeks of cycling HIT (Table 2). This is in line with previous research; however, skeletal muscle lactate accumulation is reported to be less following HIT (41). This may reflect an increased efficiency of lactate shuttling following HIT because it has been demonstrated that there is an increase in skeletal muscle and heart lactate transporters (2,28,40). This would allow for a greater transfer of lactate around the body and may reflect a better buffering capacity for the skeletal muscle (45).
In conclusion, the present data show that only 6 sessions of 6 × 10-second all-out cycling sprints over 2 weeks performed alongside normal training is an effective method for recreationally competitive runners to improve running performance. The differences in the magnitude of the improvement in 3-km TT, time to exhaustion, V[Combining Dot Above]O2peak, PPO, and MPO between the 3 groups suggest that performance adaptations are dependent on the work-to-rest ratio. Thirty-second rest in between sprint bouts seems to have a detrimental effect on power production in subsequent sprints, whereas 120-second rest seems to be too long to induce favourable endurance adaptations. Therefore, 80-second rest seems optimal when targeting both power and endurance adaptations.
These data demonstrate that cycling HIT has the “transferability” of training effect to running performance by providing sufficient training stimulus to improve a number of important variables. Most importantly, the non–weight-bearing nature and minimal eccentric contraction of leg muscles during stationary cycling (23) offer runners and other athletes a low-volume alternative modality that could minimize the risk of overuse injury. Furthermore, evidence suggests that doubling of training workload does not lead to an increase in performance in well-trained participants (12). Therefore, a relatively fast performance gains with a reduced training volume makes it a time-efficient method of training, which could be used during a taper period, a preseason training, and the times of traveling. Finally, this type of training could also be used by athletes during a rehabilitation period who are recovering from injuries that prevent them from running.
The authors thank the participants for their time and effort.
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