Research Review: Boost Strength, Endurance, and Flexibility

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Chris Beardsley is a co-founder of Strength and Conditioning Research, a monthly publication that summarizes the latest fitness research for strength and sports coaches, personal trainers, and athletes. The views expressed herein are his.

Photo by Justin Singh

The fitness industry can be a confusing place, with many experts providing conflicting opinions. Scientific research is our best shot at providing objective and effective approaches to fitness. Strength and Conditioning Research is a monthly review service that covers new and interesting scientific studies on fitness topics. The studies included help answer difficult questions about optimal fitness, training, and body transformation.

Here are the summarized results of three recent studies that were covered in the review along with what those results mean for us.

Do You Have to Stretch Every Day to Become More Flexible?

Researchers led by Daniel Cipriani from Chapman University, Orange, California, found stretching 3-4 times a week was almost as effective at improving flexibility as doing it every day [1].

What did the researchers do?

The researchers recruited 62 subjects (30 male and 33 female, age range of 18-46 years) and asked them to complete a four-week hamstring-stretching program.  However, there were four separate programs that varied in frequency.

One group did stretched daily, twice a day. A second stretched once a day. A third stretched 3–4 days a week, twice a day. The fourth stretched 3–4 days a week, once a day.

The stretch was a standing one-legged hamstring movement where the target leg was elevated. Each time the subjects performed the movement, the position was held for 30 seconds, followed by a 10-second rest and then a second 30-second stretch.

What happened?

The researchers found that all four groups gained an average of 18.1 ± 6.3 degrees of hip range of motion as a result of the increased hamstring length.  There was no significant difference between the groups.

However, the researchers did find that when they collapsed the data from the groups that stretched daily and the groups that stretched just 3-4 times per week, the high-frequency groups did achieve slightly better results.

What did the researchers conclude?

The researchers concluded that both daily and 3-4 times a week frequencies of stretching produced similar gains in range of motion. However, they also concluded that the higher frequency programs produced slightly greater improvements.

What does it mean for you?

If stretching is a high priority, doing it every day will lead to faster improvements. However, if you are short of time and stretching is just one small part of your training, then just 3–4 times a week will provide results that are almost as good.

Can We Combine Resistance and Endurance Training?

A group of researchers led by Jacob Wilson from the University of Tampa, Florida, recently performed a detailed review of the literature and found that programs involving both resistance and endurance training can lead to reduced gains in power but not strength or size [2].

What did the researchers find?

For strength and power athletes

The researchers found that combined resistance training and endurance training programs did not produce significantly lower gains in strength or hypertrophy adaptations compared to strength-only programs. However, they did find that combined resistance training and endurance training programs produced significant lower power gains than strength-only programs.

For endurance athletes

The researchers concluded that combined resistance training and endurance training programs did not result in lower gains in maximal oxygen uptake than endurance training, suggesting that endurance athletes can make use of strength training without fear of compromising their performance.

What does it mean for you?

If you are an athlete whose sport requires maximal power or the ability to produce a large force in short period of time (i.e. throwing, jumping, sprinting), it's best to avoid or minimize endurance training.

If you are an athlete whose sport requires just strength and size, or you just want to improve the way you look, you can make use of combined resistance and endurance training without fear of the endurance training limiting your gains.

Finally, for endurance athletes, make use of strength training within a combined resistance- and endurance-training program with no adverse affects on fitness.

Can Interval Training Improve Triathlon Performance?

Researchers from the UK, led by John Jakeman of Oxford Brookes University, found that extremely short-duration, high-intensity interval training can be used to improve triathletes’ endurance performances [3].

What did the researchers do?

The researchers investigated whether short-duration high-intensity interval training, involving six sessions of 10 sprints of 6-seconds for a total of 60-seconds of exercise per session could lead to performance improvements in a 10 km cycling endurance time trial.

They recruited 12 sub-elite triathletes with a minimum of two years experience and divided them into two equal groups for cycling training. One group took part in high-intensity interval training and the other continued endurance training as normal. The groups continued their swimming and running training as if nothing had changed.

What happened?

After two weeks on the program, the researchers tested all of the subjects in the time trial and found the group that had performed intervals had improved significantly, while the group that had performed traditional endurance training had remained at basically the same level.

What did the researchers conclude?

The researchers concluded that very short bouts of high-intensity exercise over a two-week period can improve aerobic performance.

What does it mean for you?

While sprint intervals of only six seconds are unlikely to prepare us for an entire triathlon, they appear to be a very effective way of making quick improvements to our aerobic performance if we are generally used to longer-distance training.

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Works Cited

  1. Effect of stretch frequency and sex on the rate of gain and rate of loss in muscle flexibility during a hamstring-stretching program: a randomized single-blind longitudinal study. Cipriani, D.J., Terry, M.E., Haines, M.A., et al. Department of Physical Therapy, Chapman University. Journal of Strength and Conditioning Research. 2012 Aug;26(8):2119-29.
  2. Concurrent training: a meta-analysis examining interference of aerobic and resistance exercises. Wilson, J.M., Marin, P.J., Rhea, M.R., et al. Department of Health Sciences and Human Performance, The University of Tampa. Journal of Strength and Conditioning Research. 2012 Aug;26(8):2293-307.
  3. Extremely short duration high-intensity training substantially improves endurance performance in triathletes. Jakeman, J., Adamson, S., Babraj, J. Department of Sport and Health Sciences, Oxford Brookes University, Oxford. Applied Physiology, Nutrition, and Metabolism. 2012 Oct;37(5):976-81. Epub 2012 Aug 2.

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