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The Problem with Workout Trends: HIIT, F45 & Spinning

The pandemic-induced sedentary lifestyle has led to weight gain and mental fatigue. This has resulted in fitness and wellness becoming increasingly emphasized. Many workout trends are sweeping the fitness industry today, from HIIT to F45.

But are all these workout trends worth the hype? Just how beneficial are they really? Here’s an in-depth analysis for you.

High-Intensity Interval Training (HIIT)

High-Intensity Interval Training (HIIT) emerged as a popular exercise since it’s quick and has proven effective1. HIIT, by definition, utilizes planned intensity and work to rest/recovery ratios in unlimited variations2. This training involves short bursts of intense exercise followed by periods of low-intensity exercise or rest.

The period of intense exercise can be anywhere between 45 seconds to a few minutes, and the same applies to periods of rest. 15 to 20 minutes is the ideal time frame for high-intensity interval training.

A key reason for the popularity of HIIT is its perceived time savings. Intermittent exercise can elicit a similar physiological response to traditional moderate-intensity continuous training (MICT). This is despite a smaller total exercise volume and time commitment3.

Are there side effects to this Workout Trend?

But, while being effective, high-intensity exercises has shown to sometimes cause unfavorable effects, including rhabdomyolysis. Rhabdomyolysis is a serious condition of muscle injury and acute kidney injury (AKI), and they may be deleterious to long-term health outcomes. This is especially evident in poorly trained or sedentary individuals4.

A study has shown that HIIT can induce early and progressive muscle injury in many of the individuals assessed. CK elevation indicative of rhabdomyolysis was observed in 19% of the participants5. 19% of participants developed elevated CK indicative of rhabdomyolysis.

A high CK level in a blood sample usually signifies muscle destruction and could be an indication of rhabdomyolysis.

F45 Training

F45 Training refers to functional training in 45 minutes6. The training focuses on strength and endurance training and provides a functional full-body workout.

The F45 training combines HIIT and circuit training to move your body in different ways and at different speeds. It promotes muscle growth, enhances aerobic capacity, burns calories, and maintains lean muscle mass.

F45 has also been classified as the same style of workout as HIIT. In some cases, high-intensity exercises can cause detrimental consequences and injuries.

Despite F45 marketing itself as being ‘well-suited to individuals of all fitness levels’, it may still be extremely demanding physically for some, let alone people who do not have the habit of exercising but are looking to lose weight7.

In spite of being under the supervision of trainers during the session, the group of people who are unable to keep up with the ‘demands’ of the workout may increase the chances of injuring themselves from overexertion.


Spinning or indoor cycling is another form of high-intensity exercise. The most popular workout is indoor cycling as it is suitable for most people regardless of their level of fitness.

Several studies have analyzed the effect of indoor cycling on several parameters related to health. These parameters include maximal oxygen consumption, blood pressure, and body composition. It also includes biochemical markers such as HDL or LDL8.

Most spinning classes take place in energetic and entertaining environments. Every session begins slowly and gradually picks up speed and intensity, similar to cycling on flat terrain.

Despite the popularity of spinning, little research has been conducted to document physiological responses to the workout9.

Similar to HIIT, rhabdomyolysis does occur. Research has shown that high exercise intensities may pose a risk factor for catastrophic outcomes in middle-aged and older individuals10.

When too much Exercise become Dangerous

Despite being efficient in burning the most calories within a short period of time, high-intensity workouts can be stressful for your body and muscles.  Even the fittest individuals can cause themselves damage if they push themselves beyond their endurance limits.

As a result of peer pressure and the enthusiastic support of other attendees, many participants adopted a mentality of “go big or go home”.

Many may feel the urge to overdo it in such an intense atmosphere.

Experiencing some muscle soreness for the next couple of days is normal as your overused muscles are beginning to heal. However, for some, overexertion could lead to rhabdomyolysis.

The Dangers of Rhabdomyolysis

Rhabdomyolysis can be a life-threatening condition caused by muscle breakdown and muscle death11. This condition could be direct results from overexertion, trauma, toxic substances, or disease.

As muscle cells disintegrate, they release a protein called myoglobin into the blood. The kidneys are responsible for removing this myoglobin from blood so urine can flush it out of the body. In large quantities, myoglobin can cause damage to the kidneys. The most serious late complication that could develop is acute renal failure, which occurs in approximately 15% of patients who suffer from the condition12.

Marathon runners, riders, and other high-intensity interval exercisers have a higher risk of developing the condition due to the overexertion of their muscles.

Not a Good Idea for Weight Loss

Workout trends such as HIIT and F45 are fine, but people who do not work out regularly should not rely on these workouts to lose fat.

When you’re new to exercise, it’s highly recommended that you avoid performing these strenuous workouts right away. This kind of high-intensity training might cause muscle injury and put your body at risk.

After a hard workout, your body tends to be particularly low on blood sugar. Regardless of nutrition value, you may find yourself ravenous and grab any food available. You may even end up replacing the calories you are worked so hard to burn off.

Post-workout, there is a psychological shift where being “good” gives you permission to be “bad.” It is possible to overeat after a high-calorie workout if you think that you have “earned” it.

There is no magic pill for weight loss and no exercise, no matter how intense, can replace a healthy diet.

And as you grow more frustrated, you may start to feel out of control or doubt your own level of self-discipline. Let’s get down to targeting these diet-resistant stubborn spots. Here are some alternatives that you may consider.

Finding the Right Formula

For the most part, the stress that HIIT puts your body under is beneficial – as it’s this stress that drives change in your body.  The trendiest workouts are not for everyone and there is nothing wrong with that.

It’s impossible to adopt strenuous workout routines immediately, especially for people who don’t exercise regularly.

Non-invasive fat removal treatments can help you finally target stubborn fat that has been resistant to exercise. Schedule a body appointment to find out which solution is best suited for you, or click here to explore our solutions.