What is a “hiccup”
To begin with, it should be noted that there is no generally accepted definition of ‘warm-up’ or any clear criteria.
A warm-up is usually understood as a series of low to medium intensity exercises for 5-10 minutes immediately after training or competition. This type of recovery is also called recovery training.
Among the 89% of US athletic trainers who recommend active warm-ups, 53% say jogging is the best option (source).
Professionals’ doubts about the necessity of a warm-up
The post about the doubts on the necessity of the warm-up as a mandatory element of the training session caused a lot of interest and a flurry of comments.
A review of research on the effects of warming up on recovery, injury, sports performance
Active hiccups have received relatively little attention in science, and there have never been any studies analysing them. This is why, until recently, we were unaware of its actual usefulness. Finally, two sports scientists, Bas van Horen from the Netherlands and Jonathan Peek from Australia, reviewed the available publications and compared the effects of different types of active and passive warm-ups on performance, injury, long-term adaptive response and psychophysiological recovery after training. Their review was published in Sports Medicine in 2018.
Here are the most interesting dry data to them from that study. And looking ahead, no specific recommendations were found for the mandatory inclusion of a warm-up in the training process either.
Warm-ups do not help improve performance in elite athletes when they train again after 4 hours
Italian researchers compared the effectiveness of a 20-minute active recovery workout (land or water aerobic exercise and stretching) and a passive recovery workout after a standard training session for young American football players. After a 4-hour rest period, the subjects (elite athletes) performed several anaerobic tests – a 10-metre sprint and vertical jumps. Both types of active warm-up had little or no effect on running times and jump heights, or even slightly worsened them. Similar results were shown by futsal players in another study.
The evidence on the effect of the warm-up on the performance of the next day’s training is contradictory
Researchers examined military personnel, American football and indoor football players, weight-lifting athletes, long-distance runners, football players and girls playing netball, amateur athletes, just physically active people and untrained participants. In most cases the effect was marginal, sometimes the subjects gained some benefit and at other times the recovery training reduced the performance.
There is also conflicting evidence about the effect of a cooldown on lactate elimination rates
There is plenty of evidence to suggest that different low- and medium-intensity exercises reduce blood and muscle lactate concentrations more effectively than passive recovery. Other researchers have found no significant difference, and some even believe that a passive warm-up clears lactate from the blood and muscles faster. But even if the warm-up slightly speeds up lactate excretion, experts have not yet found any particular practical benefit: according to scientists, after an intense workout, blood lactate levels return to resting levels within about 20-120 minutes without any recovery exercise anyway.
Hardening does not help to reduce delayed muscle soreness
An active warm-up increases blood flow to the skin and muscles. This process can improve muscle nutrition, reduce muscle soreness and speed recovery. However, most studies conducted with physically active people and professional athletes did not find that active warm-up was more effective than passive warm-up in reducing delayed muscle soreness from 0-96 hours after exercise.
Effect of warm-up on CNS and peripheral nervous system recovery
Intense exercise causes fatigue of the central and peripheral nervous system, which can worsen the results of subsequent training or competition. But even here, an active warm-up will not help. In any case, a 20-minute run as an active warm-up, which ended about an hour after a high-intensity workout, did not improve the neuromuscular function of the athletes. In other studies, running combined with static stretching had no effect on the contractile properties of the biceps femoris in professional football players, and water exercise did not improve the reaction time of long-distance runners. This is not to say that active cooldown did not improve neuromuscular and contractile function at all, but the effect was not significant.
Hardening does not speed up glycogen re-synthesis in muscles
High-intensity exercise depletes muscle glycogen stores, which can worsen performance over the next 24 hours. To avoid this, athletes often take carbohydrates after training. Active huddling can theoretically increase glycogen resynthesis in muscle, as it increases muscle blood flow and therefore glucose supply, while muscle contraction increases glucose transporter GLUT-4 synthesis. However, researchers see no difference in the rate of glycogen synthesis after an active and passive workout, and sometimes the recovery exercise even makes things worse.
Warm-up and recovery of the immune system
During recovery from high-intensity or prolonged exercise, the immune system can be depressed and the athlete is vulnerable to infection. Rapid recovery after exercise reduces the chance of upper respiratory tract diseases, and there is little research on this effect. An active warm-up is better than a passive one, preventing a decrease in white blood cell count immediately after exercise, but not after 120 min. There is no difference between the effects of active and passive warming up after 24 hours. So, if active cooldown has any effect on the number of immune system cells, it is within two hours of training. Whether it affects disease incidence is unknown.
An active warm-up improves cardiovascular and respiratory performance
The cardiovascular and respiratory systems work actively during exercise to provide blood and oxygen to the muscles. These systems do not immediately go into a resting state after exercise, and an active warm-up is expected to speed up this process. Both active and passive warm-ups restore the heart rate (HR) to normal, but active warm-ups do so faster. In contrast, other studies have found passive warm-up to be more effective, but the HR was measured between 1-5 minutes post-exercise, so the work is of no practical relevance.
Active cooldown brings respiratory indices such as minute respiratory volume, respiratory rate and oxygen deficit back to normal more quickly.
Immediately after exercise, athletes are vulnerable, becoming dizzy and visually impaired and sometimes losing consciousness. It is thought that recovery exercises can prevent these fainting spells by increasing blood flow to the heart and brain due to muscle contraction, preventing blood stagnation in the legs and preventing (theoretically) an increase in the partial pressure of carbon dioxide in the arteries. Indeed, there is evidence that active warming up increases blood flow in the legs and forearms, but whether these effects prevent post-exercise fainting is unknown.
Zipping does not help hormone concentrations recover after exercise
The level of physiological stress and psychological well-being of an athlete can be judged by the rate at which hormone concentrations recover after exercise. However, four studies show that active cooldowns do not help hormone levels better than passive cooldowns.
Moreover, an active cooldown, such as running on an incline treadmill, can delay recovery of plasma adrenaline, noradrenaline and cortisol levels immediately after exercise, but has little effect on hormone concentrations half an hour after exercise compared with a passive cooldown.
Warm-up has no effect on injury rates
The effect of warm-up on injury is poorly understood, and is usually studied in combination with stretching and warm-up. In three prospective cohort studies, regular warm-up does not reduce the likelihood of injury in runners. In another cohort study of runners, the combination of warm-up, warm-up and stretching also had little effect on their injury incidence. Preliminary evidence suggests that active warm-up has no effect on injury rates, although its effect may depend on the type of recovery exercise, its duration and the sport.
Conclusion and implications
For the most part, active cooldown has not been shown to improve performance on the same day or the following day, but there are reports that it creates benefits that are felt on the following days.
An active warm-up does not prevent injury, and there is preliminary evidence that regular active warm-ups do not enhance long-term adaptive response.
An active warm-up accelerates the reduction of lactate levels in the blood, but not necessarily in muscle tissue. However, the rate of lactate reduction is generally a questionable factor in favour of hiccups.
Hiccups may partially prevent immune system suppression and provide faster cardiovascular and respiratory recovery. It is not known, however, whether it reduces the likelihood of cardiovascular complications, fainting and post-exercise illness.
Much evidence suggests that active warm-ups do not significantly reduce delayed muscle soreness or improve indirect markers of muscle injury, neuromuscular contraction properties, final muscle stiffness, movement volume, hormone concentration or measures of psychological recovery.
Hiccups can also interfere with glycogen synthesis in muscles.
In general, currently available empirical evidence indicates that active warm-ups have little or no effect on post-exercise psychophysiological well-being.