Warming up before exercise may not increase your overall strength, but new research shows it gives your muscles the speed and explosive power needed for rapid movements.
Study: The effect of muscle warm-up on voluntary and evoked force-time parameters: A systematic review and meta-analysis with meta-regression. Image credit: PeopleImages/Shutterstock.com
Muscle warm-ups before beginning exercise improve contractility; there is little data on whether active vs. passive warming is preferable. A recent review in the Journal of Sport and Health Science explored the evidence in this area, concluding that the effect of warm-ups is mostly on rate-dependent muscle contractility rather than the maximum force produced, and does not vary with the warm-up mode.
Introduction
Muscle contraction may occur voluntarily, or it may follow electrical stimulation of the neuromuscular unit. These are termed voluntary vs evoked muscle contraction, respectively.
Voluntary muscle contraction and force production require that local muscle temperature remain within the normal range, from ~35°C at rest to about 40°C during exercise. Certain muscle contractility properties, such as the rate of force development, shortening velocity, and power output, change when the temperature rises by as little as 1-2°C. Some studies suggest that the maximum force production also rises with muscle warming, but contradictory results make this less definitive.
Most research in this field has focused on passive heating, with relatively few studies directly comparing active warm-ups, prompting the current study. In addition, the effects of testing mode (evoked vs. voluntary contractions), task type, and temperature measurement method on outcomes have been insufficiently investigated.
Study findings
The current study followed a meta-analytic approach, pooling the results of 33 studies.
The study found that, regardless of other factors, raising muscle temperature within normal limits enhanced voluntary and evoked muscle contractility, particularly in measurements dependent on contraction speed. In practice, this means that rapid, dynamic force production and the rate of force development both improved moderately following warm-ups.
The latter is important when rapid acceleration or deceleration is required, especially when changing direction. Rapid force production is, conversely, key to sportspeople and clinical patients who must produce force quickly to complete an action.
Power output, which is considered a rate-dependent property, also showed an increase. In contrast, the maximum force produced did not change significantly with warm-ups. The lack of change in maximum muscle strength could be due to the small sample size or differences between studies.
Muscle performance did not differ markedly after an active vs. a passive warm-up protocol. The observed (non-significant) increase in performance with active vs. passive warm-up was possibly due to post-activation potentiation (PAP). Still, the authors cautioned that this explanation remains speculative because of limited and heterogeneous data. This is especially true of rate-dependent characteristics, suggesting that this, rather than warm-up, is responsible for the improvement.
The post-warm-up temperature did not vary with the temperature measurement method, the specific warm-up task, the individual's training status, or sex. However, the authors emphasized that the limited number of robustly designed studies (with full control conditions) weakens confidence in these subgroup analyses.
The researchers also pointed out numerous sources of potentially confounding errors that could have weakened or distorted the findings. For instance, evidence suggests a high pull specific warm-up is much more effective than a cycling warm-up.
Conversely, in the current study, the effects of specific vs non-specific warm-up protocols on performance could have been confounded by suboptimal specific warm-up routines, which caused muscle fatigue, interfered with functional patterns of muscle activation, and hindered performance.
Given the study design, other factors involved in the effects of active warm-up could not be studied in detail.
Conclusions
Increasing muscle temperature with warm-up, whether passive or active, improves rate-dependent contractile function and muscle power. However, the maximum force produced does not change significantly in evoked or voluntary muscle contraction.
The mode of warm-up does not significantly influence the final effects. The authors stress, however, that this lack of difference may reflect methodological limitations rather than a genuine absence of effect.
These conclusions need to be examined in larger groups for more robust analysis. For instance, factors that affect the outcome in active warm-up could not be separately assessed here, potentially contributing to the lack of difference between active and passive warm-up protocols.
Future research should examine the effects of temperature on electrical stimulation parameters. This is important for understanding both evoked muscle twitch parameters and the effects of electrical muscle stimulation, which is used to train and test muscle contraction in diverse clinical groups.
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