Warming up before exercise is commonplace in sport and considered essential to facilitate optimal performance (41). There is, however, uncertainty regarding its effectiveness in combination with stretching protocols (10,29,32,39) and particularly before high-intensity intermittent running sports such as soccer, rugby, and field hockey. As a result, warm-up routines are typically based on trial and error or the individual philosophies of the athlete and coach (5-7).
Warm-up techniques can be divided into two categories: active and passive. Active warm-up brings about both metabolic and thermoregulatory changes through dynamic exercise such as running. Passive warm-up, however, elevates body temperature by external means such as hot water immersion. Passive warm-up before exercise has consistently been associated with improved high-intensity performance, including maximal voluntary contraction (11) and maximal cycling (13,36,37). These immediate improvements in performance have been attributed to an increased anaerobic adenosine triphosphate (ATP) turnover, muscle fiber conduction velocity, and an improved efficiency of cross-bridge cycling in the sarcomere (14,19), reducing the time to peak tension and half-relaxation time (1,2,9,17,34,38).
Active warm-up is reported to improve maximal cycling (13,19,33) and supramaximal kayak (7) performance. The putative mechanisms facilitating performance remain elusive, yet may include an exercise hyperemia, a residual metabolic academia and the associated benefits on oxygen disassociation, pyruvate dehydrogenase activation (18,20), and subsequent speeding of the oxygen kinetics as indicated by an elevated baseline oxygen consumption (V̇o2) (3,20). Furthermore, an active warm-up that reduces pH before exercise has also been linked with a blunted blood lactate response during exercise, possibly due to an increased availability of acetyl groups and hence accelerated oxidative metabolism (20).
It is not clear whether a warm-up facilitates repeated sprint performance. To date, only 2 studies have investigated the effects of warming up on high-intensity intermittent exercise (21,31). Mohr et al. (31) reported a significantly improved repeated sprint time (3 × 30-meter field sprints with 25-second active recovery) when preceded by a submaximal active warm-up (7 minutes, 60% maximum heart rate, (HRmax)). Conversely, Gregson et al. (21) reported that active and passive warm-ups increasing core temperature (Tc) to approximately 38°C reduced running time to exhaustion (∼60 minutes) during an intermittent motorized treadmill test (repeated 30 seconds at 90% V̇o2max and 30 seconds at 30% V̇o2max). Although high in internal validity, the performance measures and the performance modes of previous research are limited in the external application to running-based intermittent sports. The assessment of intermittent running performance in a laboratory environment would clearly add ecological validity, especially in terms of sport specificity and external control. The laboratory-based nonmotorized treadmill ergometer (27,28) allows the athlete to generate his or her own running speed and provides reliable measures of running speed during both discrete sprints and repeated sprint exercise (24,40).
Therefore, the aim of the present study was to investigate the effects of both active and passive warm-ups on high-intensity intermittent running using nonmotorized sprint treadmill ergometry.
Experimental Approach to the Problem
The subjects were required to visit the laboratory 5 times during a 2-week testing period with a minimum of 24 hours separating each test. Each subject was instructed not to consume any products of nutritional value 2 hours before testing and to abstain from alcohol, caffeine, and strenuous exercise in the previous 24 hours. Subjects were required to complete a food diary 24 hours before and the day of the first trial and instructed to repeat this routine for all subsequent trials. During the first visit, anthropometric characteristics were measured including height, body mass (Seca 770 digital scales, Seca, Birmingham, UK), body fat (Harpenden callipers; Baty International, Burges Hill, UK), and [overdot]Vo2max. During the second visit, subjects completed a habituation protocol on a nonmotorized treadmill. For the remaining 3 visits (mean laboratory conditions ± SD: ambient temperature 20.1 ± 1.2°C; relative humidity 32.4 ± 4.3%; barometric pressure 755 ± 6 mm Hg) each participant was required to perform a repeated sprint protocol on the same nonmotorized treadmill, preceded by a submaximal active warm-up (10 minutes of motorized treadmill running at 70% V̇o2max; mean Tc: 27.8 ± 0.2°C), a passive warm-up (hot water submersion 40.1 ± 0.2°C until Tc reached that of the active warm-up; 10 minutes ± 23 seconds), and no warm-up (control; 10 minutes of quiet sitting). The warm-up techniques were based on those previously incorporated into intermittent exercise research designs (21,31). The active warm-up was performed during trial 1 to provide a target Tc for the passive trial; subsequently, the passive and control trials were randomized. Each warm-up condition was followed by a 10-minute static recovery period in which subjects remained seated adjacent to the sprint treadmill (Figure 1). No stretching was permitted throughout any of the previous warm-up trials. Subjects were instructed to wear shorts, a T-shirt, and outdoor running footwear suitable for maximal sprinting.
Ten male semiprofessional standard soccer players (mean ± SD) age: 22.0 ± 1.0 years, height: 1.80 ± 0.06 meters, body mass: 79.2 ± 5.7 kg; body fat: 12.5 ± 3.1%, and V̇o2max: 55.6 ± 4.8 mL·kg−1·min−1 agreed to take part in the study approved by the university ethics committee. After a full explanation of the procedures and potential risks, all subjects provided written informed consent.
To determine baseline aerobic fitness and provide the specified exercise intensity for the active warm-up, V̇o2max was determined using an incremental test to exhaustion on a motorized treadmill (H/P/Cosmos; Quasar, Nussdorf-Traunstein, Germany). Subjects warmed up for 5 minutes at 8 km·h−1 on a 1% gradient. The gradient was then increased to 4% and the speed subsequently increased by 1 km·h−1 every minute to volitional tolerance. Verbal encouragement was given during the test. Exhaustion was defined using the criteria of the British Association of Sport and Exercise Sciences (4). Throughout the V̇o2max test, expired pulmonary gases were collected breath by breath and averaged over 30 seconds using online gas analysis (Jaeger Oxycon Pro; Viasys Healthcare, Hoechberg, Germany). The gas analysis system was calibrated before each test with gases and volumes of known concentration using an automatic electronic calibration.
Subjects completed a standardized habituation protocol on the nonmotorized treadmill (Sprint Runner; Hoggan Health Industries, Draper, UT). Previous research has shown that there are no differences in running speed between 2 repeated sprint trials on a nonmotorized treadmill when the first visit is preceded by a prolonged warm-up on the ergometer (24). The habituation protocol used in this study is therefore deemed sufficient to familiarize all subjects with this form of treadmill ergometry. A 5-minute warm-up at a self-selected speed was followed by a 2-minute static recovery period, after which the subjects completed first 5 minutes of variable speed running and second 10 six-second maximal sprints with a 34-second static recovery, i.e., identical to the experimental trial. Before all sprinting trials, subjects were instructed to exercise maximally during all sprints.
Subjects completed 10 six-second maximal sprints from a standing start with a 34-second static recovery (i.e., each sprint starting every 40 seconds) preceded by either an active, passive, or no warm-up (control). The work-to-rest ratios and timings of this repeated sprint protocol are similar to those published elsewhere (9,12,15,16,22,24). On completion of the warm-up and subsequent 10-minute rest period, the subjects were transferred to the nonmotorized treadmill. Immediately before the repeated sprint test, the subjects straddled the nonmotorized treadmill belt and secured a harness around their waist. The harness was attached to a nonelastic tether and secured to a precalibrated wall-mounted strain gauge (Tedea Huntleigh Ltd., Cardiff, UK). The height of the strain gauge was adjusted to ensure that the tether was perpendicular to the treadmill belt. The nonmotorized treadmill was interfaced with customized data acquisition software (Picolog, Hardwick, UK) recording running speed (m·s−1) at 10 Hz. The experimental set-up is identical to that described previously (40). As the subjects initiated each sprint from stationary and in accordance with previous literature using a similar ergometry system (27,40), the peak speed attained within 1 second (MxSP) was calculated using a 1-second rolling average. MxSP was defined as the sum of the highest MxSP per sprint divided by the number of sprints. MxSP has been shown to be highly reliable in the assessment of repeated sprint running with a coefficient of variation of 2.75% and confidence interval of 1.89%-3.8% (24). Performance fatigue of MxSP was calculated using the percentage of decrement method (fatigue = (100 − ((total sprint MxSP/ideal MxSP) × 100))) (15,16).
Expired pulmonary gases were collected using Douglas bag procedures pre-warm-up, post-warm-up, and pre-exercise to measure the effects of the warm-up on pulmonary oxygen consumption and hence aerobic metabolism. Douglas bag samples were subsequently analyzed immediately after the experimental trial for the volume of expired air (Harvard dry gas meter 230 V; Harvard Apparatus, Holliston, MA) and concentrations of oxygen and carbon dioxide (Servomex 1440C; Servomex Group Ltd., Crowborough, UK).
HR was recorded every 5 seconds during the experimental trial using HR telemetry (Polar S610, Polar Electro Oy, Kempele, Finland).
In order to quantify the temperature effects of each warm-up and to match Tc of the passive warm-up to that of the active warm-up, Tc was recorded pre-warm-up, post-warm-up, pre-exercise, immediately after, and 10 minutes after exercise during the experimental trial. Tc was measured using a flexible rectal probe inserted 10 cm past the anal sphincter and linked via a flexible cord to a digital thermistor-recording device (Model CD; Edale Instruments, Cambridge, UK).
Blood samples were measured to assess the effects of previous warming on the exercise blood lactate concentration ([lac−]B). Arterialized capillary blood samples were drawn from the ear lobe (20 μL) and subsequently analyzed for [lac−]B (Biosen C-Line; EKF Diagnostics, Barleben, Germany). The blood analysis system was calibrated before each test with a standard solution of known concentration (12 mmol·L−1). Blood samples were taken pre-warm-up, 1-minute after warm-up, pre-exercise, and 2, 4, and 6 minutes after exercise (Figure 1). Previous research has reported that peak [lac−]B occurs within approximately 6 minutes after repeated sprint exercise (12).
The physiological variables (Tc, HR, baseline V̇o2, and [lac−]B) and the performance measures (MxSP and percentage of decrement in MxSP) were analyzed using a 1-way analysis of variance with repeated measures. Homogeneity of variance was confirmed using Mauchly's test of sphericity. Violations of sphericity were corrected using the Greenhouse-Geisser adjustment. Where a significant F ratio was reported, differences were identified by a Scheffé post hoc test; a priori α was set at 0.05. Statistical analyses were conducted using the SPSS (Version 11.5, SPSS, Chicago, IL). All data are reported as mean ± SD unless stated otherwise.
The MxSP per sprint for each condition are summarized in Figure 2. The percentage of decrement MxSP, peak MxSP and group MxSP for all warm-up conditions are summarized in Table 1. There were no differences observed in MxSP between the active and passive trials (p > 0.05) and no significant differences in the percentage decrement of fatigue between all conditions. However, peak MxSP and group MxSP were significantly greater in the active and passive trials compared to the control (p < 0.05).
Tc during the active, passive, and control trials are summarized in Table 2. Post-warm-up, Tc was significantly elevated in the active and passive trials compared to pre-warm-up (p < 0.05) and compared to the control trial (p < 0.05). Pre-exercise Tc was greater in the passive trial compared to the active and control trials (p < 0.05). Immediately post-exercise, Tc was increased in all trials compared to pre-exercise (p < 0.05) and also significantly higher in the passive trial than the active and control trials (p < 0.05).
Pre-warm-up, there were no differences in V̇o2 between all trials (active: 6.75 ± 3.08 mL·kg−1·min−1; passive: 5.38 ± 1.60 mL·kg−1·min−1; control: 5.92 ± 1.53 mL·kg−1·min−1; p > 0.05). However, post-warm-up, V̇o2 increased significantly in both the active (14.59 ± 2.15 mL·kg−1·min−1; p < 0.05) and passive (8.17 ± 1.13 mL·kg−1·min−1; p < 0.05) trials compared to rest and the control (4.76 ± 1.53 mL·kg−1·min−1). Pre-exercise V̇o2 was reduced in the active (6.44 ± 3.06 mL·kg−1·min−1; p < 0.05) and passive trials (6.02 ± 1.46 ml·kg−1·min−1; p < 0.05), such that there were no differences in V̇o2 pre-exercise compared to rest in all conditions (p > 0.05).
Pre-exercise HR was significantly greater in the active trial (91 beats·min−1) compared to the passive (84 beats·min−1) and control (74 beats·min−1; p < 0.05) trials. During the repeated sprint test, mean HR was significantly greater in the active (149 ± 13 beats·min−1; p < 0.05) and passive trials (142 ± 13 beats·min−1; p < 0.05) compared to the control (134 ± 15 beats·min−1; Figure 3).
[lac−]B during the active, passive, and control trials are summarised in Table 3. Post-warm-up, [lac−]B was significantly greater in the active trial than in the passive and control trials (p < 0.05). Pre-exercise, there were no significant differences in [lac−]B between all trials. Post-exercise, peak [lac−]B was significantly greater than pre-exercise in all trials and significantly greater in the active trial compared to the control (p < 0.05).
The aim of this study was to investigate the effects of both active and passive warm-ups on high-intensity intermittent running using nonmotorized treadmill ergometry. There are 3 main findings of this study. First, there was no difference in high-intensity intermittent running speed when preceded by either an active or passive warm-up. Second, there were no significant differences in measures of performance fatigue between all conditions, and, third, both active and passive warm-ups significantly improved repeated sprint running speed compared to no warm-up.
The findings of this study are similar to those of Mohr et al. (31). Although Mohr and colleagues did not incorporate a passive warm-up into their research design, they reported that during the 15-minute half-time period of a soccer game, compared to no warm-up, subjects who engaged in a static recovery for 7 minutes and then completed a 7-minute low-intensity active re-warm-up (60% HRmax) significantly improved repeated sprint time. The authors suggested that the improvement in performance may be related to a maintained muscle temperature (Tm) and potential neuromuscular benefits such as the sustained speed of muscular contraction, although the latter was not measured.
The speed of muscular contraction and rate of force application are highly temperature dependent (2). Previous research has suggested that an active warm-up may increase the neural stimulation of fast-twitch A (FTA) motor units above that of a passive warm-up (8,26). Koga et al. (25) also suggest that an elevated HR and V̇o2 before exercise as observed in this study may be indicative of increased FTA muscle fiber recruitment. These mechanisms, in conjunction with an elevated Tc and Tm, may increase arterial-venous oxygen difference due to a reduction in mitochondrial inertia and facilitated metabolic processes at the onset of exercise, reducing the time required to return to a resting state during recovery periods. However, recently, it has been shown that a passive warm-up also increases both anaerobic ATP turnover and muscle fiber conduction velocity in predominantly FTA muscle fibers (19). That repeated sprint performance and the decrement of performance fatigue were not different in both the active and passive trials of this study suggests that there may be similar neuromuscular mechanisms acting on the muscle fiber membrane and the contractile properties of the sarcomere. This is similar to results of previous studies (13) that also found very small differences in power output (∼0.5%) during 20-second maximal cycling after active and passive warm-ups. Indeed, Mohr et al. (31) state that sprint performance is directly related to Tm, suggesting, in relation to the present findings, that the additional metabolic effects associated with an active warm-up may not provide a performance stimulus greater than that achieved through passive warm-up alone, particularly if both modes increase Tc and Tm.
Although matched for post-warm-up Tc, immediately before exercise, Tc was greater in the passive trial and continued to increase, such that 10 minutes after exercise, Tc was greatest in the passive trial (Table 2). This continual increase in Tc may have implications for prolonged intermittent performance. It is suggested that performance is impaired when Tc reaches a critical level; furthermore, it was reported that increasng Tc to approximately 38°C before exercise reduces intermittent running time to exhaustion (21). Therefore, a passive warm-up that increases Tc to a level commensurate with an active warm-up and that continues to increase during rest periods, the exercise itself may impair prolonged high-intensity intermittent performance due to the earlier attainment of a critical Tc. To fully elucidate these effects, future studies should aim to match both post-warm-up and pre-exercise Tm and Tc before both short and prolonged duration repeated sprint exercise.
Although [lac−]B was greater after the active warm-up, there were no differences immediately before exercise in all conditions. Furthermore, a blunted lactate response was not observed in any trials in this study. Previous studies that have reported a blunted [lac−]B have used a recovery duration post-warm-up of 5 minutes compared to 10 minutes in this study. Furthermore, evidence of a blunted lactate response has occurred when preceded by either a prolonged moderate- or high-intensity intermittent warm-up, resulting in a much greater increase in [lac−]B (18,23,30,35). Methodological differences and limitations of this study may, therefore, account for the disparity between the current and previous findings. In particular, previous studies (18) have measured muscle lactate concentration as opposed to [lac−]B. When measuring muscle lactate, any change in lactate concentration would reflect a direct change in muscle metabolism. When measuring [lac−]B, the systemic concentration is determined by both the rate of appearance and rate of disappearance in the blood, and, hence, a specific reduction in muscle lactate production during the experimental trial may be overshadowed by an increased rate of appearance of lactate in the blood, potentially masking a blunted lactate response. However, a number of studies (23,35) have reported a blunted [lac−]B when measuring finger prick blood samples, suggesting that this may not be the case.
It is, therefore, not clear whether a residual metabolic acidemia and a subsequent blunted blood lactate response associated with an active warm-up per se are present or would benefit high-intensity intermittent exercise. Dawson et al. (12) reported that there was no change in post-exercise systemic [lac−]B during repeated sprint exercise (6 × 6-second maximal sprinting) on a cycle ergometer with varying recovery durations (10-60 seconds). Since variable recovery durations up to 60 seconds do not influence [lac−]B, this may suggest that an increase in lactate or the associated changes in pH do not provide a performance benefit greater than that of a passive warm-up or an indication of muscle metabolism during repeated sprint exercise. Instead, the increase in post-exercise [lac−]B in this study may provide a global indication of systemic metabolic demand, specifically, the increased activity of lactate dehydrogenase in maintaining cytosolic redox potential and anaerobic ATP production. This suggests that additional physiological mechanisms may be associated with the improvement in repeated sprint performance after both active and passive warm-ups, such as the improved efficiency of voltage-gated Na+ channels, improved SR Ca2+ pump activity, an increased anaerobic ATP turnover, and the activation of myosin heavy chain FTA fibers (19).
In conclusion, there were no differences in high-intensity intermittent running performance after active and passive warm-ups. The findings of this study suggest that both temperature and no temperature mechanisms may facilitate repeated sprint exercise and that the putative mechanisms for this improvement may include neuromuscular facilitation and the increased efficiency of contractile and recovery processes. Despite the different metabolic and physiological responses to previous warming, this study provides novel findings suggesting that the magnitude of improvement in high-intensity intermittent running is similar when preceded by either an active or a passive warm-up and that undertaking a warm-up facilitates high-intensity intermittent running performance greater than when no warm-up is performed.
Engaging in a warm-up before exercise is considered essential to ensure optimal performance and to reduce the potential for injury. This study suggests that before high-intensity intermittent running sports such as soccer, rugby, and field hockey, engaging in either an active or a passive warm-up that elevates Tc to a similar level will improve performance more than not engaging in a warm-up. However, due to the practical and temporal limitations of a passive warm-up and that a passive warm-up may result in a continual increase in Tc throughout intermittent exercise (Table 2), a submaximal active warm-up may be more appropriate, particularly if the exercise duration is prolonged (>60 minutes) in order to optimize performance.
The authors gratefully acknowledge the expert assistance provided by the exercise physiology staff and technicians in the Human Performance Laboratory at the University of Wales Institute, Cardiff. The authors have no conflicts of interest.
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