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Gas exchange and lactate threshold are valid indicators of moderate-intensity aerobic exercise, rat study finds

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Gas exchange and lactate threshold are valid indicators of moderate-intensity aerobic exercise, rat study finds
Credit: Andrea Piacquadio from Pexels

Researchers at University of Tsukuba identified a previously unconfirmed gas exchange threshold in rats and demonstrated that this threshold, together with the lactate threshold, serves as an indicator of moderate-intensity exercise to determine the effectiveness of training in enhancing aerobic performance.

The study is published in Medicine & Science in Sports & Exercise. This achievement is fundamental for basic research on exercise. It will be useful for researchers in the field of health and fitness promotion as it provides a useful moderate-intensity index for rats.

During incremental aerobic exercise, there are thresholds where blood lactate levels begin to rise, and CO2 production increases rapidly relative to O2 uptake. The former threshold is termed the lactate threshold (LT), and the latter, the gas exchange threshold (GET). In humans, these thresholds are moderate-intensity exercise indices, with LT and GET at 45%–74% of the maximal oxygen uptake (VO2max). Training at or above these thresholds improves aerobic performance.

In contrast, in rats, LT has been identified, but GET is not known yet. Furthermore, it is unclear whether the rat GET and LT can be useful indicators of exercise intensity similar to the thresholds in humans.

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The researchers previously established a rat model for identifying the LT during running exercise. This study aimed to simultaneously identify LT and GET by integrating this LT model with the standard human GET identification method, known as the V-slope method.

Subsequently, the relationships among the identified GET, LT, and VO2max, as well as the changes in these thresholds following aerobic training below or above the LT, were examined. The results showed that GET and LT in rats occurred synchronously at intensities ranging from 41.0% to 65.5% VO2max, and that the maximal (VO2max) and submaximal (GET, LT) aerobic capacities were enhanced only in rats that trained at intensities above the LT.

These results suggest that the GET and LT in rats are valid indices of moderate-intensity exercise in training prescription to enhance aerobic performance as in humans. The findings of this study are expected to serve as a catalyst for further research in the field of rat studies focused on exercise intensity, ultimately contributing to the advancement of human exercise prescription strategies. In particular, the noninvasive and easily identifiable nature of the GET from the exhaled gas suggests a wide range of potential applications.

More information:
Koshiro Inoue et al, Setting Treadmill Intensity for Rat Aerobic Training Using Lactate and Gas Exchange Thresholds, Medicine & Science in Sports & Exercise (2024). DOI: 10.1249/MSS.0000000000003562

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Do you have sore hips? I asked a pain specialist why this happens and how to improve it

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Do you have sore hips? I asked a pain specialist why this happens and how to improve it

Hip soreness is a terribly common issue—it’s something that I certainly suffer with—so I’m always trying to get to the bottom of where this soreness originates from and what you can do about it.

According to Dr Shady Hassan, MD, an interventional pain and sports medicine physician and the founder of NefraHealth, immobility is the root cause of this discomfort.

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“No Pain No Gain” May Be Wrong: Science Says Slow Eccentric Exercise Builds Stronger Muscles

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“No Pain No Gain” May Be Wrong: Science Says Slow Eccentric Exercise Builds Stronger Muscles

Modern exercise culture has spent years glorifying exhaustion. The harder a workout feels, the more effective people assume it must be. Sore muscles became badges of honor, while gentle movements were often dismissed as ‘not real exercise.’ 

A man lifting a dumbbell. Image credits: Andres Ayrton/Pexels

However, according to a new study, some of the most efficient ways to build muscle strength may happen during the slow, controlled moments people usually ignore—walking downstairs, lowering weights, or carefully sitting into a chair. 

Study author Kazunori Nosaka, who is the director of exercise and sports science at Edith Cowan University, argues that eccentric exercise—a type of muscle action that occurs while muscles lengthen under tension, may offer a more practical alternative. Its opposite, concentric exercise, is the shortening (lifting) phase where muscles produce force to overcome resistance.

Instead of demanding maximum effort, these movements appear to train muscles while placing less stress on the body.  

“The idea that exercise must be exhausting or painful is holding people back. Instead, we should be focusing on eccentric exercises which can deliver stronger results with far less effort than traditional exercise – and you don’t even need a gym,” Nosaka said.

Muscles work differently on the way down

The study examines decades of earlier research on eccentric exercise rather than presenting a single laboratory experiment. It focuses on a simple but often overlooked detail of human movement, which is how muscles behave differently depending on whether they are shortening or lengthening.

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When someone lifts a dumbbell, climbs stairs, or rises from a chair, muscles shorten as they generate force. Scientists call this a concentric contraction. Eccentric contractions happen during the opposite phase—when the muscle stays active while stretching. 

Examples include lowering the dumbbell back down, descending stairs, or slowly lowering the body into a seated position. According to the review, muscles can tolerate and produce greater force during eccentric actions while using comparatively less energy and oxygen. 

“Eccentric contractions are distinguished by their ability to generate greater force than concentric or isometric contractions, while requiring less metabolic cost,” Nosaka notes.

Researchers believe this happens because muscles act more like controlled braking systems during lengthening movements, resisting gravity rather than directly overpowering it. As a result, people may gain strength without putting the same level of demand on the cardiovascular system. 

This difference could make eccentric exercise especially useful for individuals who find traditional workouts physically overwhelming.

“Eccentric exercise training provides numerous benefits for physical fitness and overall health, making it suitable for a wide range of individuals from children to older adults, clinical populations to athletes, and sedentary to highly active people,” Nosaka added.

Gravity may be doing more training than we realized

To support this argument, the study brings together findings from several earlier research works. For instance, one study from 2017 tracked elderly women with obesity who repeatedly walked either upstairs or downstairs over a 12-week period. 

While climbing stairs is normally considered the tougher workout, the women assigned to walk downstairs showed stronger improvements in measures including blood pressure, heart rate, and physical fitness. The results suggested that resisting gravity during downward movement may provide a surprisingly powerful training effect.

YouTube videoYouTube video

The review also discusses eccentric cycling, where participants resist pedals driven backward by a motor instead of pushing them forward in the usual way. 

Although the movement feels unusual and requires concentration, earlier studies found it improved muscle power, balance, and cardiovascular health while feeling less exhausting than standard cycling workouts.

Another important part of the review addresses muscle soreness, one of the main reasons eccentric exercise never became widely popular outside rehabilitation settings. People often experience delayed onset muscle soreness, or DOMS, after unfamiliar eccentric workouts. 

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“Unaccustomed eccentric exercise is often associated with muscle damage characterized by delayed onset muscle soreness (DOMS) and a reduction in muscle force-generating capacity lasting more than a day. However, this effect diminishes or at least is attenuated when the same eccentric exercise is repeated (known as the repeated bout effect),” Nosaka explained

Many eccentric exercises require little or no equipment. Slow squats into a chair, heel-lowering movements, controlled wall push-ups, or even maintaining posture against gravity can activate eccentric muscle work. 

Moreover, some studies referenced in Nosaka’s review suggest that just a few minutes of these exercises each day can still produce measurable improvements in health and strength.

The future of fitness may feel less punishing

The findings challenge the mindset surrounding fitness itself. Many people abandon exercise routines because they associate physical activity with pain, fatigue, or lack of time. Eccentric exercise suggests that effective movement does not always need to feel extreme. 

If future research continues to support these findings, eccentric exercise could influence far more than gym routines. It may reshape physical rehabilitation, elderly care, injury recovery programs, and public-health recommendations aimed at increasing physical activity among sedentary populations. 

These exercises also place lower demands on the heart and lungs while still strengthening muscles. They could help people who are unable or unwilling to follow intense training programs.

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Nosaka suggests that “we should establish eccentric exercise as standard practice, and make it common, accessible, and widely accepted as the ‘new normal’ of exercise to improve life performance and high (athletic) performance.”

However, this does not mean eccentric exercise is a universal replacement for all forms of physical activity. The current paper is a review of previous studies, and its findings still need to be validated through experiments and large-scale clinical trials.

Nosaka also notes that “Future studies should investigate mechanisms underpinning the effects of eccentric exercises in comparison to other types of exercises (e.g., isometric exercises, concentric exercises, aerobic exercises),”  

This could help scientists design safer and more personalized exercise programs for different age groups and health conditions.

The study is published in the Journal of Sport and Health Science.

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Flexibility expert recommends doing this for three minutes daily to improve mobility

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Flexibility expert recommends doing this for three minutes daily to improve mobility

Longevity is something of a buzzword right now, and the idea of living better for longer is undoubtedly appealing. Mobility is a key component of this.

By definition, mobility is the ability to move freely, something that tends to deteriorate as we age. But there are simple things we can do to maintain it.

One of them is “joint flossing”, a daily practice recommended by experienced coach and mobility specialist Darren Ellis.

“Mobility is a conflation of strength and flexibility,” he says. “I always used to believe that strength was the foundation of everything in exercise. But if you’re strong and you can’t move through a decent range of motion at certain joints, you’re still suffering.

“When you reach down to pick something up from the floor and it seems further away than it used to be, you suddenly realise how crucial mobility is.”

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Below, Ellis explains how to use his three-minute joint flossing protocol to help ease stiff joints and improve your ability to move.

How to try joint flossing

The body works on a rough “use it or lose it” basis. If you rarely move a joint through its full range of motion, the tissues around it can become tight, stiff and sore. The natural remedy for this is gradually reintroducing movement in the affected areas.

“The easiest place to start when improving mobility is to get the joints moving more freely with some simple joint circles,” says Ellis. “I sometimes call it joint flossing because, firstly, you are flossing nutrients through the joint by promoting blood flow in this area, and secondly, it’s something you should do regularly.”

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You start with neck circles then work your way down your body from your head to your toes, as shown in the video above – if something can move, you move it.

Ellis recommends doing five to 10 repetitions per body part, using a controlled tempo and a range of motion that feels safe and comfortable for you.

“There’s no need to force anything,” he says. “You’re just giving your body a chance to move again.”

Doing this consistently will improve your physical capacity and mobility, allowing you to return to other movements and exercises over time.

Read more: Five stretches you should be doing every day, according to a flexibility expert

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