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To ice or not to ice? Icing promotes muscle regeneration after mild injury

Cumulative research by a multi-institutional Japanese research collaboration reveals that ‘to ice or not to ice’ may depend on the degree of muscle injury.

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Applying ice to a muscle injury is a widespread first-aid treatment, but exactly what effect does this have on the muscle regeneration and does it really help? Cumulative research by a multi-institutional Japanese research collaboration reveals that ‘to ice or not to ice’ may depend on the degree of muscle injury.

In their latest research, the group consisting of Associate Professor ARAKAWA Takamitsu and Master’s student NAGATA Itsuki (from Kobe University’s Graduate School of Health Sciences), and Assistant Professor KAWASHIMA Masato (Kawasaki University of Medical Welfare) et al. have shown that applying ice to muscle damage in a small percentage of muscle fibers in rats promotes muscle regeneration. This is believed to be the first study in the world to show benefits of icing on muscle repair. In conjunction with their previous study on serious muscle injuries (‘Icing muscle injuries may delay recovery’), it is hoped that these results can be used as a basis for more accurate guidelines on whether or not to ice such injuries.

These research findings were first reported in the American Journal of Physiology-Regulatory, Integrative and Comparative Physiology on March 6, 2023.

Main Points

  • The experiments showed that applying ice after a mild muscle injury promotes muscle regeneration.
  • This is believed to be the first time in the world that a study has shown a positive effect of icing on muscle regeneration.
  • The researchers showed that the extent of the injury may have a greater impact on the effectiveness of icing than the method or timing employed.
  • The findings of this ongoing research will lead to the spread of more accurate information on the effects of icing throughout hospitals, and in the realms of sports and physical education.

‘RICE treatment’ is a common approach for treating the acute phase of sports injuries. This acronym stands for Rest, Ice, Compression and Elevation and it is also often used in physical education in schools and even clinical settings. There are a variety of subsequent steps that can be taken to treat the injury afterwards, yet opinions vary as to whether or not icing should be applied. However, there is a lack of evidence on the benefits of icing.

The current research team has conducted many experiments to investigate the effectiveness of icing, which led them to publish their previous findings (‘Icing muscle injuries may delay recovery’ ). However, no previous animal experiments have indicated that icing promotes muscle regeneration.

In this study, the researchers focused on altering the severity of the muscle injury in the experiments. The reasoning behind this was that the majority of sports-related muscle injuries are limited; in other words less than 10% of the overall number of muscle fibers (myofibers) are damaged and necrotized. However, all animal experiments up until now had looked at more serious injuries where over 20% of the myofibers were damaged.

Thus, the team devised an animal model for mild muscle injuries, and experimented with applying ice after injury using a similar method as before.

After the animal was anaesthetized, the muscle was exposed and clamped between forceps to induce injury. In their previous experiments, the researchers attached a 500g weight to the forceps, which induced an injury that affected 20% of the total number of fibers in the muscle. In the present study, they tried attaching a 250g weight to the forceps and demonstrated that this could be used to consistently injure 4% of the fibers (Figure 1). This is similar to the degree of injury that often occurs after sports activities such as vigorous exercise or long-distance marathon running.

Icing was carried out by placing polyethylene bags of ice on surface of the skin over three 30-minute sessions per day, with each session being 1.5 hours apart. This was continued until two days after injury for a total of 9 icing sessions (i.e. immediately after injury = 3 sessions, 1 day after injury = 3 sessions, 2 days after injury = 3 sessions). The icing method was the same as in the previously reported study (‘Icing muscle injuries may delay recovery’).

Observations of muscles that were regenerating in the icing group and no-icing group 2 weeks after injury revealed significant differences in the size of regenerating fibers in cross-sections (Figure 2). In other words, this demonstrated the possibility that skeletal muscle regeneration is promoted by icing.

Macrophages are immune cells that orchestrate the reparative process of injured muscle. Pro-inflammatory macrophages accumulate in the damaged site soon after injury occurs, however they express an inducible nitric oxide synthase (iNOS), which has a disadvantageous side-effect of expanding the injury’s sizeThe results of this team’s experiments revealed that icing after mild muscle injury reduces the accumulation of iNOS-expressing pro-inflammatory macrophagesBy causing this phenomenon, icing prevents the expansion of muscle injury size.

In other words, icing attenuates the recruitment of pro-inflammatory macrophages in the injury site. This was also reported in their previous study (‘Icing muscle injuries may delay recovery’), demonstrating that this is an effect caused by icing regardless of whether the muscle injury is serious or mild. In the previous study, icing was found to delay the regeneration of muscle after a serious injury that destroyed many fibers because the pro-inflammatory macrophages were unable to sufficiently phagocytose (*5) the injured muscle. In contrast to this, the current study shows that icing has a positive effect when the muscle injury is mild because it prevents the secondary expansion of the muscle injury caused by the pro-inflammatory macrophages. It suggests that this particular effect of icing is connected to the promotion of muscle regeneration.

Icing has been used in the treatment of muscle injuries for a long time, however the positive effects of icing had yet to be elucidated until now. This study has shown that icing can promote muscle regeneration when used to treat commonly-occurring mild muscle injuries.

However, this does not mean that icing is effective for all types or degree of muscle injury. The researchers aim to further elucidate and raise awareness of this. For example, the group’s previous study showed that icing actually inhibited regeneration in cases of serious muscle injury. In addition, the term ‘muscle injury’ also includes extremely minute injuries that have yet to be observed through the team’s animal experiments, so it is still unclear as to what effect icing has on the repair from such microtraumas.

The researchers’ next challenge is to determine the extent of muscle injury up to which icing is appropriate. By building upon their previous investigations, they aim to contribute towards guidelines that will enable people in sports and clinical rehabilitation to make accurate judgements about whether or not to ice an injury.

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Move to quit: Exercise boosts smoking quit rates

Researchers found that people taking part in exercise programs were 15% more likely to achieve continuous abstinence and 21% more likely to report not smoking over a seven-day period, compared with control groups.

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A pack-a-day smoker can spend around $14,000 a year on cigarettes, yet despite the financial and health costs, quitting remains one of the most difficult changes many people will ever attempt.

Now, new research from Adelaide University shows that exercise can help people quit smoking by reducing cigarette consumption, easing cravings and improving their chances of quitting.

Researchers found that people taking part in exercise programs were 15% more likely to achieve continuous abstinence and 21% more likely to report not smoking over a seven-day period, compared with control groups.

They also found that exercise could reduce cigarette consumption by two cigarettes per day, and that a single bout of exercise immediately reduced cigarette cravings for up to 30 minutes after exercise.

The systematic review and meta-analysis examined 59 randomised controlled trials involving more than 9000 participants, exploring the effects of both single bouts of exercise and long-term exercise programs on smoking cessation, cravings, withdrawal symptoms and mood.

Globally, tobacco smoking remains the leading preventable cause of premature morbidity and mortality, accounting for about 7 million deaths, including an estimated 1.6 million non-smokers who are exposed to second-hand smoke.

Around the world, e-cigarette use has now reached more than 100 million people.

The researchers say exercise should be viewed as an additional tool that can be used alongside established smoking cessation support.

Lead researcher, Dr Ben Singh said the findings provide smokers with a practical, low-cost tool that can support their quitting journey.

“Quitting smoking is one of the best things a person can do for their health, but it’s also one of the hardest,” Dr Singh said.

“Many smokers want to quit, but the current approaches don’t work for everyone. That’s why we need more strategies that people can incorporate into their daily lives at little or no cost.

“Something as simple as regular exercise can make a meaningful difference to people trying to quit, helping them manage cravings, smoke less and improve their chances of quitting.”

While smoking rates have reduced over the past two decadesdemand for e-cigarettes and heated-tobacco products have risen, targeting the younger generation.

Today, 80% of the 1.3 billion tobacco users worldwide live in low- and middle-income countries, yet in contrast, vaping has risen across many OECD countries.

Senior researcher Adelaide University’s Professor Carol Maher said exercise could be used strategically to ward off tobacco cravings.

“Quitting smoking does not have to begin and end with willpower alone,” Prof Maher said.

“Cravings can be difficult to manage, but they often pass. Our review found that even a single bout of exercise can reduce cravings for up to 30 minutes, which may help people get through some of the hardest moments of a quit attempt.

“Exercise should not replace evidence-based quit supports such as counselling and smoking cessation medication, but it may be a practical, low-cost strategy that people can use alongside them.”

The researchers say the next step is to test how exercise can be built into real-world quit programs, including digital, community and clinical services, and to examine whether it can also support people trying to quit vaping, where evidence is currently lacking.

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Wellness

Midlife fitness linked to longer, healthier lives

Researchers note that improving fitness during midlife may be a key strategy for promoting healthy aging and preserving quality of life later on, even with modest increases in physical activity.

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How fit you are in midlife may help determine not just how long you live, but how many of those years are spent in good health, according to a study published in the JACC, the flagship journal of the American College of Cardiology.

The study found that adults with higher levels of cardiorespiratory fitness in midlife lived longer lives, developed fewer chronic diseases and spent more years free from serious illness compared with those who were less fit.

Cardiorespiratory fitness—how well the heart and lungs supply oxygen during physical activity—is known to reduce the risk of heart disease and early death. This study extends prior research by showing that fitness also plays a meaningful role in healthy aging, defined as years lived without major chronic disease.

The findings indicate that higher fitness in midlife is strongly associated with later onset of chronic disease, lower overall disease burden and longer life expectancy. These benefits were observed in both men and women.

Researchers followed more than 24,500 men and women who were healthy through age 65 and tracked their health outcomes later in life using Medicare data. Fitness was measured earlier in adulthood using a treadmill test, and researchers examined the development of 11 major chronic conditions, including heart disease, diabetes, kidney disease and cancer.

Compared with people who had low fitness levels, those with high fitness in midlife experienced clear benefits later in life. On average, they developed chronic diseases at least 1.5 years later, had fewer total conditions and lived longer overall. These patterns were seen in both men and women and across different ages, body weights and smoking histories.

Importantly, the study emphasizes health span—not just lifespan—highlighting that fitness helps people live more of their lives in good health, not simply live longer with disease.

The findings also underscore the public health value of physical activity, as cardiorespiratory fitness can be improved through regular movement such as brisk walking, cycling or other aerobic exercise.

Researchers note that improving fitness during midlife may be a key strategy for promoting healthy aging and preserving quality of life later on, even with modest increases in physical activity.

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Wellness

Adding resistance training improves strength and aerobic fitness, better for heart health

Aerobic training and resistance training independently improve aerobic fitness, walking distance, muscle strength, and HRQoL.

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Heart failure affects more than 64 million people worldwide (1%–3% in the general adult population) and its prevalence is projected to increase. This condition is commonly categorized into 2 main types: heart failure with reduced ejection fraction (HFrEF; where the heart is too weak to pump enough blood to meet the body’s needs) and heart failure with preserved ejection fraction (HFpEF; where the heart becomes stiff and cannot relax sufficiently to fill with enough blood).

Regardless of type, heart failure is a life-threatening condition characterized by low exercise tolerance, progressive functional decline, reduced health-related quality of life (HRQoL), and a high risk of hospitalizations, morbidity, and mortality. The study led by Tasuku Terada was published in the Journal of Sport and Health Science.

Previous studies have shown that aerobic training and resistance training independently improve aerobic fitness, walking distance, muscle strength, and HRQoL. Some studies have also demonstrated superior benefits of high-intensity interval training (HIIT) on aerobic fitness and cardiac function in patients with heart failure when compared to traditionally used moderate-intensity continuous training.

However, despite the well-established benefits of each exercise modality, the effects of combining aerobic training and muscle strength training (i.e., combined training) compared to the routinely recommended aerobic training alone were not clear in patients with heart failure. In this study, the researchers compared the effects of combined training and aerobic training alone on aerobic fitness, muscle strength, and HRQoL in patients with heart failure. These comparisons were made while accounting for heart failure classifications (i.e., HFrEF or HFpEF), total exercise duration (i.e., matched or unmatched exercise session duration between combined and aerobic training alone), and exercise type (e.g., HIIT). 

The researchers systematically searched databases for studies directly comparing the effects of combined training and aerobic training alone on aerobic fitness, walk test distance, muscle strength, and HRQoL in patients with heart failure. Of 13,965 studies they screened, 15 studies were included (466 patients with HFrEF (89%) and 60 with HFpEF (11%); 17% female).

Pooled analyses showed that, in HFrEF, combined training increased aerobic fitness, walk test distance, and upper body muscle strength more than aerobic training alone. The superior effects of combined training on aerobic fitness and walking distance were retained when exercise session duration was matched between the two exercise modalities, indicating that combined training has a greater impact on these measures independent of total exercise duration. HIIT combined with muscle strength training also increased aerobic fitness more than HIIT alone.

No differences were found between combined and aerobic training alone in lower body muscle strength or HRQoL. Overall adherence to combined training was high or comparable to that of aerobic training alone.

Similarly, dropout rates in the combined training group were comparable to those in aerobic training alone, and no notable differences in the risk of adverse events were observed. 

To summarise, in predominantly male patients with HFrEF, combined training yielded greater improvements in aerobic fitness, walking distance, and upper body muscle strength than aerobic training alone.  These results highlight that, when prescribing exercise for a fixed time frame, allocating time to both aerobic training and muscle strength training may be a more effective strategy for improving aerobic fitness in patients with HFrEF.

Additionally, because HIIT may improve aerobic fitness more effectively while requiring less time than moderate-intensity continuous training, combining HIIT with muscle strength training may offer a time-efficient approach to improve aerobic fitness in patients with HFrEF.

Considering the absence of notable differences in adherence or adverse events, these findings support that replacing part of aerobic training with muscle strength training may be an effective strategy for patients with HFrEF to increase aerobic fitness, walking distance, and muscle strength, all of which are important predictors of better prognosis in patients with heart failure. Further evidence is needed to clarify the effects of combined training in HFpEF.

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