Warm-up before physical exercise has been a widely accepted practice for many decades. The purpose of active warm-up activities before physical exercises is to enhance physical performance, to reduce muscle soreness, and to prevent sports-related injuries by increasing the body temperature (15,28,33,34), whereby light warm-up (at 30% V̇o2max) proved to have the most favorable influence on heart rate (HR) and oxygen consumption during exercise (3,7,9). The onset of acute exercise is associated with an increase in energy turnover and an increase in O2 demand. Organs involved (i.e., the respiratory system, the cardiovascular system and the muscle metabolism), need a certain time to adapt to the new circumstances, which results in a temporary mismatch between O2 supply and O2 demand. Warm-up procedures can help to minimize this imbalance by shortening the duration of the temporary mismatch and increasing the energy efficiency. However, data on the optimal conditions that may promote improved performance show conflicting results, because study designs are difficult to compare (11,17,23,25). Studies differ not only in the study population (from well-trained athletes to completely untrained subjects) but also in the duration, intensity, and recovery period of the procedure. Furthermore, the comparison between active warm-up activities, such as physical exercise and passive warm-up procedures, such as the raise of muscle or core temperature by some external means, is missing completely.
The majority of studies have investigated the influence of different intensities of active warm-up on physical performance. Active warm-up is suggested to induce major cardiovascular and metabolic changes, including increased lactate-energy provision, enhanced oxygen release, etc. (1,13). Further effects have been attributed to temperature-related mechanisms. These include decreased muscle and joint stiffness and increased nerve-conduction rate (6,37).
Evidence suggests that local or systemic modification in body core temperature or skin temperature can modify metabolic and circulatory responses to exercise in a similar way as active warm-up (16). Modalities used in sports medicine clinics to passively raise tissue temperature include ultrasound, short-wave diathermy, and warm-water immersion, all of which have shown to induce an increase in deep muscle temperature of between 3.4 and 3.8°C after 10-30 minutes of treatment. However, only a small number of clinical studies on humans investigated the effect of such measures on the physical outcome (9-11).
A direct comparison between active or passive warm-up procedures before exercise on the metabolic and biomechanical response of the organism is missing completely. In addition, the effect of warm-up, active or passive, before exercise, on muscle strength, and the risk of injury has not been conclusively evaluated, yet. The aim of the present investigation was to quantify the beneficial effect of preheating before exercise on energy supply and muscle strength performance and to compare between active and passive warm-up procedures. To measure conditions that may have an impact on performance capacity the metabolic and respiratory outcome parameters of o2 uptake, HR, pH value, and lactate were defined as endpoints. Possible mechanism by which warm-up could improve physiological conditions for improved performance could include facilitated oxygen delivery, because hemoglobin releases oxygen more readily at higher temperatures (Bohr effect), increased blood flow through active tissues, and lowered viscous resistance within active muscles (5). Furthermore, it is known that specific enzyme systems of the glycolytic pathway, such as phosphofructokinase, are influenced by variations in pH. For example, acidosis is associated with an inhibition of lipolysis, and has been shown to limit endurance time (19).
The null hypothesis of the present investigation was to not find a difference between the endpoints in either procedure. However, we expected to detect better outcome parameters after warm-up modalities before exercise than after no warm-up at all.
Experimental Approach to the Problem
To investigate a possible difference between metabolic response after active vs. passive warm-up procedures before physical exercise the following parameters were determined: V̇o2 uptake in L·min−1 (standard temperature, pressure, dry [STPD]) to determine the individual endurance performance capacity, which corresponds to the o2 uptake, HR (1 min−1), which is a direct measure of exercise intensity, pH value, as a measure of metabolic balance of the organism and lactate (mmol·L−1), as a measure of muscle metabolism.
Twenty healthy male volunteers, aged 18-28 were enrolled into this controlled prospective crossover study. Subjects were untrained, with a V̇o2max of 90-110% of the norm. The study was performed in accordance with the Declaration of Helsinki (1964). Approval and written consent from the local ethics committee of the Medical University of Vienna, and Institutional Board approval for the research, were obtained in accordance with the local legal requirements before the initiation of the study. For safety reasons, the physician was present during the whole study period.
Inclusion criteria were to not be involved in regular endurance or strength training to rule out training as a confounding factor, and abstaining from intense exercise in the preceding 24 hours before the study. A 2-hour fasting period before testing was also required. Exclusion criteria were any current medical drug treatment or any sign of abnormality in health status (obtained from anamnesis, Electrocardiography, or labor chemistry), in particular systolic blood pressure-levels at rest >150 mm Hg. An increase of the systolic blood pressure during exercise >260 mm Hg was a criterion to stop the exercise test.
Physical Exercise Protocol
In a preliminary test, all 20 volunteers underwent a stepwise incremental spiroergometer test (Sensormedics, SensorMedics Corp, Yorba Linda, CA, USA; Ergometrics 900, Ergoline, Windhagen, Germany) to determine their maximal endurance performance capacity, which corresponds to their individual maximal O2 uptake. Starting with a work load of 50 W, work rate was increased by 25 W every 2 minutes (after the protocol of the Austrian Association of Cardiology) until the subject could not maintain the cycling cadence of 80 rpm. Then, on separate days, 3 spiroergometer-test series were performed, the first without prior warm-up, the second with a standardized active warm-up procedure preceding the test, and the last with a passive warm-up procedure of musculature of both lower limbs before testing. A time span of 3 minutes was required between either warm-up procedure and the test session.
All tests were performed after previously cycling at 20 W over 3 minutes at a cycling cadence of 80 rpm. After 10 seconds, the load was increased to 80% of individual V̇o2max values for a period of 6 minutes, during which measurements were made. All test experiments were performed at the same time of the day on the same calibrated ergometer. Three days of rest were scheduled between the preliminary test and the 3 exercise tests.
Active Warm-Up Procedure
The active warm-up procedure consisted of cycling on a cycle ergometer at an exercise intensity corresponding to 35% of the subjects' individual V̇o2max for 20 minutes.
Passive Warm-Up Procedure
The passive warm-up procedure consisted of a water bath of both lower limbs at a temperature of 39°C for 20 minutes. A small plastic pool was used for this purpose. A constant temperature was maintained by refilling the pool with hot water. The temperature was controlled throughout the test.
During each of the 3 test series the following parameters were determined 3 times every 2 minutes and in the first and last minutes of recovery: V̇o2 uptake in L·min−1 (STPD) to determine the individual energy turnover, HR per minute, pH value, and lactate in mmol·L−1 (Eppendorf® E SAT 6661 Lactat, Eppendorf AG, Hamburg, Germany).
To test maximal strength (1 repetition maximum, 1RM), a seated leg press on a dynamometer (Concept2Dyno, Concept 2 Ltd, Wilford, Notts, United Kingdom) was performed at the end of all 3 test sessions. Two movements using little strength were followed by 1 movement using maximal performance. The variable measured was strength (muscle peak power [in kilopond]) for extension of both legs for the full range of motion.
Paired Student's t tests were used to compare the test parameters of the 3 different test sessions. No warm-up was compared with active warm-up and with passive warm-up and finally, active warm-up was compared with passive warm-up. The paired test was used because all the different tests were done by the same persons and no sample was used more often than twice. A p-level ≤ 0.05 were considered significant. The calculation of sample size was based on an alpha level of 0.05 and a power level of 0.80. We considered correction of alpha level according to Bonferroni. We used Stata, Version 10 for statistical analysis.
There were no statistically significant differences of basal measurements between the 3 test procedures (data not shown). Detailed results of the selected parameters, including mean values and SD and the p values derived from the paired t test, separated for the 3 test procedures are listed in Table 1. The first column compares no prior warm-up with the active warm-up procedure, the second column compares no prior warm-up with the passive warm-up procedure, and the third column compares the active with the passive warm-up procedure.
Comparing no prior warm-up with the active warm-up procedure, we found a nonsignificant trend for higher HR values, higher lactate values, lower pH, and lower V̇o2 values for all time points of measurement after the no prior warm-up test procedure. Comparing no prior warm-up with the passive warm-up procedure, we found a trend for lower HR values after the no prior warm-up test procedure. pH values were significantly lower at the fourth test minute (p < 0.004) and lactate values were significantly higher at the sixth test minute and the third minute of recovery (p < 0.01 and p < 0.010, respectively) after the no prior warm-up test procedure. Comparing the active warm-up procedure with the passive warm-up procedure, there was a trend toward lower pH values and higher lactate values for the active warm-up procedure. Heart rate was significantly lower at the fourth and sixth test minute (p < 0.033 and p < 0.011, respectively) and V̇o2 values were significantly higher at the fourth and sixth test minutes (p < 0.015 and p < 0.022, respectively) after the active warm-up procedure. After alpha level correction, results were no more significant for HR at the fourth and V̇o2 at the sixth test minute (p > 0.0166).
There were no differences for strength for extension of the legs, as measured by dynamometry between the 3 test procedures.
Both active and passive warm-up procedures before exercise have been postulated to induce advantageous effects on the metabolism and skeleton of the organism. Most of these data result from animal experiments, investigating the influence of active warm-up activities. Noonan and Garrett supported the theory that warm-up of muscles of rabbits before exercise results in improvement of athletic performance and muscle injury prevention (27). In more detail, Safran et al. attributed the beneficial effect on injury prevention to an increased elasticity of the muscle-tendon unit (31). In 1945, it was argued that the effects of warm-up could largely be attributed to temperature-related mechanisms, whereby the velocity of reactions within the cell were shown to increase by 13% per increase of temperature of one degree (2). In that context, it would be reasonable to assume that passive warm-up procedures before exercise, which simply increase body temperature, would be of a similar benefit to athletes as active warm-up procedures.
The main finding of the present investigation was that healthy young male adults showed higher peak V̇o2 values, but lower HRs, during a constant load-spiroergometer test after an active warm-up procedure than after a passive warm-up procedure. Obviously, athletes reach the steady state of metabolic pathways faster after active warm-up activities than after passive warm-up activities. Our interpretation of these findings is that active warm-up procedures may allow subsequent tasks to begin with higher baseline V̇o2 values than passive warm-up procedures. A plausible explanation may be the vasodilatory effect of active warm-up on the precapillary resistance vessels, which speeds up the blood flow to the working muscle, by lowering the vascular resistance. Furthermore, increased intramuscular temperature during the active warm-up enhances the enzyme activity, and shifts the oxygen dissociation curve to the right (20). These changes may in turn increase the aerobic energy liberation during the following intense exercise (e.g., starting a race). As a consequence, the total o2 consumption will be increased and time until reaching the o2 steady state will be shortened (6). The speeding up of the V̇o2 kinetics might be related to accelerated metabolic reactions associated with oxidative phosphorylation and increased o2 delivery to the capillaries and mitochondria (13). Our results corroborate earlier findings on greater aerobic contribution and therefore decreased oxygen deficit, after active warm-up procedures (1,24). Robergs et al. reported a transient increase in V̇o2 and a decrease in blood lactate accumulation after an active warm-up procedure (30). The authors suggest that the elevation in muscle temperature after an active warm-up procedure potentially indicates an increase in blood flow of the working muscle, thereby increasing the aerobic contribution to energy metabolism at the onset of exercise. The blunted blood lactate response observed during the active warm-up trial may be associated with an increased rate of lactate clearance through skeletal muscle activity (13). However, these earlier results compared active warm-up with no prior warm-up, whereas we provide results comparing 2 different warm-up modalities. Interestingly, differences between active and passive warm-up activities was more pronounced than differences between either warm-up procedure or no warm-up at all. The attenuation of anaerobic energy production is more distinct after active warm-up activities than after passive warm-up activities.
In a previous review, it was stated that different warm-up procedures may have variable effect on long-term, intermediate and short-time performance (7). Our results confirm earlier results on improved short-term performance after active warm-up procedures in comparison to passive warm-up procedures.
The speeding of the V̇o2 kinetics was unlikely to potentiate maximal muscle strength, as measured by dynamometry. We did not find a difference in strength for extension of the legs between the 3 test procedures. However, results from dynamometry of all 3 test sessions may have been biased by the fact that they were all performed after spiroergometry. Reports on the effects of stretching or warm-up before exercise on muscle strength performance have drawn conflicting conclusions and there is still a lack of scientific evidence to support the hypothesis that warm-up activities might serve as injury prevention: On the one hand, warm-up of muscles was postulated as a way to prevent strain injury of both, tendon (22,36) and muscle tissue (27,31,35). Beneficial effects were related at least in part to an increase in muscle strength. On the other hand, other authors postulated that warm-up had no significant effect on strength during dynamometric test sessions (12). One possible explanation for the missing effect of warm-up on muscle strength in our investigation might be that the temperature effects on muscle elastic properties of muscle tissue are very small (8). Furthermore, it has been described that muscle temperature reaches its equilibrium only after 10-20 minutes of exercise (32). The duration of our test sessions might therefore have been too short to demonstrate any effect. However, the decision for the 10-minute test session was based on the fact that increasing the body temperature before exercise has shown to impair heat-storage capacity and to decrease exercise performance over longer time periods than 10 minutes (26). Future studies involving test sessions longer than 10 minutes will demonstrate whether an increase in muscle temperature results in a decrease of muscle resistance.
Interestingly, lactate values were lower after passive warm-up than after no prior warm-up and tended to be lower after passive warm-up compared to active warm-up. PH values, which were only measured once during the fourth test minute, appeared to be similar for the different test sessions, even though higher values could be detected after passive than after no prior warm-up. These results may support the earlier findings of Ingjer and Stromme (18), who found lower blood lactate concentrations and higher pH values after passive warm-up as compared to no warm-up. This may suggest that the increase in body temperature after passive warm-up has caused less anaerobic energy expenditure during the standard work after passive warm-up as compared to no warm-up. This hypothesis however, is not supported by the oxygen uptake measurements in our study (Table 1).
The lack of major distinct differences of pH values between the different test sessions may be related to the fact that warm-up is more likely to lower intracellular acidosis than to affect circulating blood pH values (21). Investigators such as Robergs et al. criticized the concept of lactic acidosis and presented alternative explanations of the biochemistry of metabolic acidosis. Metabolic acidosis is caused by an increased reliance on nonmitochondrial ATP turnover when the exercise intensity increases beyond the steady state. Under these conditions, lactate production is essential for muscle to produce cytosolic NAD+ to support continued ATP regeneration from glycolysis. Therefore, if muscle does not produce lactate, acidosis and muscle fatigue would occur more quickly (29).
In conclusion, the results of the present investigation indicate that active warm-up procedures before intense cycle ergometer exercise can increase oxidative energy metabolism during the onset of exercise. The increase in oxidative processes is accompanied by an increase in blood lactate concentrations. In addition, we assume that active warm-up has further beneficial effects on the metabolism, such as increasing muscle blood flow by vasodilation of blood vessels (4). Further research evaluating the effects of warm-up on muscle blood flow and the regulation of muscle energy metabolism during intense exercise appears warranted.
Although our study is limited by the fact that no direct performance parameters were examined, this study strongly emphasizes that active warm-up shortens the time to reach the V̇o2 steady state, decreases the oxygen deficit, and decreases the lactate level at the steady state. This would probably lengthen the time to exhaustion at the same V̇o2 or allow improved performance at the same lactate level.
For coaches and their athletes, the practical applications of these findings are that the conditions that may promote improved performance are more present after active than after passive warm-up. Even if modalities to passively raise tissue temperature, such as ultrasound or short-wave diathermy, may be useful for relaxation purposes, the metabolic and circulatory responses to exercise would be superior after active warm-up activities than after passive procedures. The results were drawn from spiroergometric tests in healthy, young male adults, and differences between active and passive warm-up were more pronounced than between either warm-up and or no warm-up.
The study was financially supported by the “Jubiläumsfond” of the Austrian National Bank. We thank David Pamphlett and Patricia Vagners for proofreading the study.
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