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High Intensity is Key for Both Cardio and Weight Benefits

strength training

Story at-a-glance -

  • To improve your cardiovascular fitness using resistance training, you must perform each exercise at maximum intensity, or “to muscle failure”
  • High level of intensity is also the key ingredient to reap maximum results from other modes of exercise besides resistance training
  • 12 weeks of high intensity interval training can not only make significant reductions in total abdominal, trunk, and visceral fat, but can also give you significant increases in fat-free mass and aerobic power

By Dr. Mercola

Researchers looking to confirm the benefits of resistance training for cardiovascular fitness found that myocardial function appears to be maintained, and perhaps enhanced, by high intensity resistance training. The results, however, depend on performing the exercises to what is referred to as "muscular failure."  

The researchers also noted that improvement in cardiovascular fitness through resistance training is possible only if intensity is high.

The results were published in the June 3 issue of the Journal of Exercise Physiology1. While previous research has demonstrated that resistance training improves cardiovascular fitness, this article offers a comprehensive, systematic review of the underlying physiological mechanisms that produce such improvement. It also quantifies the level of intensity needed to optimize results.

According to the authors:

"The results of chronic physiological adaptations demonstrate that resistance training to momentary muscular failure produces a number of physiological adaptations, which may facilitate the observed improvements in cardiovascular fitness. The adaptations may include an increase in mitochondrial enzymes, mitochondrial proliferation, phenotypic conversion from type IIx towards type IIa muscle fibers, and vascular remodeling (including capillarization).

Resistance training to momentary muscular failure causes sufficient acute stimuli to produce chronic physiological adaptations that enhance cardiovascular fitness. This review appears to be the first to present this conclusion and, therefore, it may help stimulate a changing paradigm addressing the misnomer of 'cardiovascular' exercise as being determined by modality."

Intensity is KEY When Using Resistance Training for Cardiovascular Fitness

While the belief that resistance training must be combined with some form of aerobic or endurance training to affect cardiovascular fitness is still widespread, the authors of this review question this assumption, stating that:

"Reviews looking at the effects of resistance training (RT) on the cardiovascular (CV) variables have concluded that although RT can improve such variables, it is not as effective as traditional aerobic training or concurrent training. However, methodological issues result in a certain degree of difficulty in the interpretation. The result is that such conclusive statements are questionable. The most prevalent methodological issue is that of an inappropriate definition and control of RT intensity."

As an example of such inappropriate definitions of intensity, the authors state that load is sometimes used to falsely represent intensity. But load should not be misconstrued as intensity, as intensity "is actually representative of effort," they note, "and as such only one accurate measure is possible during RT; that of 100 percent..." What they mean here is that when we talk about intensity in resistance training, we refer to maximum effort that results in momentary muscular failure.

"Consideration of this important factor leads to an entirely different conclusion than previously published," the authors state. "Where studies have appropriately controlled for intensity (as defined in this way), by having participants perform RT to momentary muscular failure, the results indicate improvements in both predicted VO2 max, and measured VO2 max in both young and older adults."

Virtually all variables involved in cardiovascular fitness have all been found to improve when resistance training is performed to failure, i.e. at maximum intensity, leading the researchers to conclude that THE most important variable with regards to improving your cardiovascular fitness using resistance training is intensity, defined as maximum effort.

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Intense Muscular Contraction Causes Physiological Adaptations that Promote Cardiovascular Fitness

The featured reviewii also notes that a high level of intensity is a key ingredient to reap maximum results from other modes of exercise besides resistance training. For example, previous research has shown that just 1.5 hours of high-intensity interval cycling per week produces similar cardiovascular adaptations and increased endurance as doing 5.5 hours of traditional slow, long-distance endurance training. The benefit of this is clear; who doesn't want to reap the same results in about a quarter of the time?!

So as long as you're doing the exercises at high enough intensity, you can replace hour-long aerobic sessions with either weight training or other modes of high intensity interval training, and reap the same or better results in terms of cardiovascular improvement, in a fraction of the time. 

"Since duration appears to be a less significant factor versus intensity in causing improvement in fitness through this modality, it is important to consider the relevance of modality and the relative merits of resistance training (notably shorter in duration and generally higher in intensity)," the authors writeiii.

"The general dichotomy drawn between resistance training (RT) and traditional aerobic or endurance training would appear unfounded. In fact, it is reasonable to conclude that modality appears to be of little relevance in producing an improvement in CV fitness since the evidenced indicates that improvement is possible by RT as long as intensity is high."

It's an excellent review of the current thinking in fitness, so if you want to learn more, I highly recommend reading through the study (which is available for free) in its entiretyiv. It goes into greater details about  the acute biological responses to resistance training, such as its impact on endurance and VO2 response; metabolic-, blood lactate-, molecular-, myocardial- and vascular responses, as well as chronic adaptations. These include metabolic and molecular adaptations, as well as improvements in your myocardial- and vascular function. The latter is thought to be the primary physiological adaptation that has the greatest impact on your cardiovascular fitness.

According to the authors:

"A plethora of research demonstrates the positive physiological adaptations that may mediate the observed improvement in CV fitness as a result of RT. It is also clear that these adaptations are, for the most part, a result of RT at high intensity (i.e., performed to failure).

... There is little evidence to support the contention that the myocardium is directly stimulated, and that any subsequent adaptations are promoted within it as a response to intense RT and so it seems unlikely that this is a mechanism involved in improving CV fitness as a result of RT. However, vascular adaptations, including capillarization, have been shown to occur within the peripheral musculature as a response to RT to failure. They are likely to contribute to the improvement in CV fitness through enhanced local muscular oxygen supply.

... It would appear that... [chronic] adaptations [produced by RT performed to failure] are not dependent upon a particular exercise modality as similar adaptations have been evidence through other forms of intense training and comparative studies of differing modalities do not clearly favor one form over another. We suggest that the key factor in determining physiological adaptations to promote CV fitness is intense muscular contraction." [Emphasis mine]

High Intensity Exercises Can Lower Your Body Fat More than Traditional Endurance Training

Another related study published in the Journal of Obesityv reports that 12 weeks of high intensity interval training (HIIT) not only can make significant reductions in total abdominal, trunk, and visceral fat, but also can give you significant increases in fat-free mass and aerobic power.  In this study, in which young overweight males were randomly assigned to either HIIT exercise or a control group, the following health benefits were achieved by the exercising group doing just 20 minutes of high intensity exercises three times a week for three months:

  • Aerobic power increased by 15 percent
  • Reduction of total fat mass: 2 kg
  • Visceral fat reduced by 17 percent

How to Properly Perform High Intensity Exercises

As discussed above, you can turn virtually any exercise into a high intensity exercise—even weight training. Earlier this year, I interviewed Dr. Doug McGuff on this, as he's a knowledgeable proponent of so-called "super-slow weight training." The reduced speed turns it into a high intensity exercise, and Dr. McGuff explains this in some detail.

Download Interview Transcript

Personally, I recommend incorporating both super-slow/high-intensity resistance training and other high intensity interval exercises into your fitness regimen, as the variety will help optimize results. In both cases, as long as you're doing the exercises at maximum intensity, you can reduce the frequency. So if you follow the Super Slow routine Dr. McGuff recommends, your weight training program can be reduced to just one 12-minute session once a week, and your anaerobic cardio to one or two 20-minute sessions a week.  

I personally don't feel comfortable yet with this approach, but I don't dispute its validity.  I still do two one-hour weight training sessions per week that have some element of super slow, but also some functional and power movements for a wide variety. I used to do three weight sessions and three high-intensity Peak Fitness exercises a week but realized that did not give me enough recovery, so I dropped down to two weight sessions and one Peak Fitness a week and that seems to be working for me now.

I recommend using a recumbent bicycle or an elliptical machine for your high intensity interval training, although you certainly can use a treadmill, or sprint anywhere outdoors. However, unless you are already an athlete, I would strongly advise against sprinting, as several people I know became injured doing it the first time that way. .

Here are the core principles:

  • Warm up for three minutes
  • Then, go all out, as hard as you can for 30 seconds
  • Recover for 90 seconds
  • Repeat 7 more times, for a total of 8 repetitions
  • Cool down for a few minutes afterward by cutting down your intensity by 50-80 percent

The first repetition is usually pretty easy as your starting heart rate is low and you can do the entire 30 seconds without stress. But since you only recover for 90 seconds your heart rate gradually continues to climb after every repetition, so hopefully by the time you finish your last repetition it is at or above your maximum heart rate.

Remember to cool down for a few minutes after your 8th repetition.

Unless you work out regularly you will likely need to slowly work your way up to 8 cycles. You can start with 2-4 and gradually increase to 8, but ideally, you should get to 8 cycles. The magic really starts to happen around repetition number 7 and 8. If you have a history of heart disease or any concern please get clearance from your health care professional to start this. Most people of average fitness will be able to do it though; it is only a matter of how much time it will take you to build up to the full 8 reps.

Aim for a Well-Rounded Fitness Program

While high intensity interval exercises accomplish greater benefits in a fraction of the time compared to slow, endurance-type exercises like jogging, I still recommend incorporating a wide variety of exercises in order to truly optimize your health. Without variety, your body will quickly adapt. As a general rule, as soon as an exercise becomes easy to complete, you need to increase the intensity and/or try another exercise to keep challenging your body.

I recommend incorporating the following types of exercise into your program:

  • Interval (Anaerobic) Training: This is when you alternate short bursts of high-intensity exercise with gentle recovery periods.
  • Strength Training: Remember to "up" the intensity by slowing it down. For more information about using super slow weight training as a form of high intensity interval exercise, please see my interview with Dr. Doug McGuff.
  • You need enough repetitions to exhaust your muscles. The weight should be heavy enough that this can be done in fewer than 12 repetitions, yet light enough to do a minimum of four repetitions. It is also important NOT to exercise the same muscle groups every day. They need at least two days of rest to recover, repair and rebuild.

  • Core Exercises: Your body has 29 core muscles located mostly in your back, abdomen and pelvis. This group of muscles provides the foundation for movement throughout your entire body, and strengthening them can help protect and support your back, make your spine and body less prone to injury and help you gain greater balance and stability.
  • Exercise programs like Pilates and yoga are also great for strengthening your core muscles, as are specific exercises you can learn from a personal trainer.

  • Stretching: My favorite type of stretching is active isolated stretches developed by Aaron Mattes. With Active Isolated Stretching, you hold each stretch for only two seconds, which works with your body's natural physiological makeup to improve circulation and increase the elasticity of muscle joints. This technique also allows your body to repair itself and prepare for daily activity. You can also use devices like the Power Plate to help you stretch.