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“We propose that intensity, in its truest sense, is the level of effort applied to a given load, defined as the number of repetitions performed in relation to the number possible.” James Fisher et al, Department of Health, Exercise and Sport Science, Southampton Solent University, UK (Medicina Sportiva, August 5, 2011)  

Intensity, What Is It?

Intensity, Failure, Rep Range, Muscular Endurance, Specificity

Just about everyone agrees that intensity is the key to building strength. But what is it? What’s the precise definition? Some contend that poundage or load is the best measure of intensity; they say heavy weights are necessary for building strength. Others say, nonsense; poundage is, at best, a nebulous measure of intensity. These people assert that effort is the only true measure of intensity—and the primary stimulus for growth of strength.

I’ve written about earlier review studies on this topic; see Forget Heavy, Think Effort and Lifting—Many Ways that Work (links below). Now we have a brand new review study from UK exercise and sport scientists James Fisher, James Steele, Stewart Bruce-Low, and Dave Smith. These researchers are from Southampton Solent University and Manchester Metropolitan University. After a comprehensive review, they “propose a set of scientifically rigorous resistance training guidelines, reviewing and summarizing the relevant research for the purpose of proposing more logical, evidence-based training advice.” (Their review includes 167 references)  

We’ll limit our discussion to intensity and related topics. As you’ll see, the UK researchers expand the discussion beyond where we’ve been before. Let’s begin with their definition of intensity.

Intensity

It’s crucial that intensity be defined in a logical and meaningful way, say the UK researchers. Strength training literature, they tell us, often uses the term as a reference to the load or poundage used. For example, intensity is expressed as a percentage of one repetition maximum (%1RM). They believe that is, at best, misguided. “We propose that intensity, in its truest sense, is the level of effort applied to a given load, defined as the number of repetitions performed in relation to the number possible,” they write. “This definition permits only one accurate measure of intensity, that of 100%; when the participant can perform no more repetitions with a given resistance.”

That makes sense, doesn’t it? Seventy percent of one repetition maximum, for example, would allow a range of reps. One person might be able to do 12 reps with 70% of one repetition maximum, while another can only do 8 reps. In short, percentage of one repetition maximum is a vague guideline. It’s not helpful as a description of intensity. What’s more, anything less than 100% intensity cannot be precisely measured.

Percentage of one repetition maximum is just what it says, a training load given as a percentage of one repetition maximum, as opposed to a measure of intensity or effort. “The problem with such a definition is the lack of any consideration of how hard the individual is working during the exercise,” the researchers write. “The definition incorrectly implies that two persons performing the same number of repetitions at a given %1RM have worked at an identical relative effort. This is, of course, not necessarily the case.”

They cite research data showing large variations between individuals in the number of repetitions possible for the same %1RM. For example, participants with a high percentage of fast-twitch muscle fibers are able to perform fewer reps with 70% of  1RM than those with a low ratio of fast-twitch fibers. This is what one would expect, because fast-twitch fibers are stronger but fatigue more quickly.

This is a big deal. Here's why.

The fuzzy nature of %1RM is an important issue, because strength training literature places so much emphasis on training intensity. It is all the more "puzzling," the researchers contend, “given that the research evidence does not support the view that training with a relatively high percentage of 1RM is important for strength development.” (More about this below)

“Therefore, when intensity is referred to within this article we are referring to the percentage of momentary muscular effort being exerted, not %1RM, and we would suggest for consistency and accuracy in the literature, other authors follow suit.”

Momentary Muscular Failure

Momentary musculature failure means the inability to perform any more positive repetitions in good form against a given resistance. It’s synonymous with maximum effort. As we’ve seen, maximum effort is not one and the same as a given percentage of one rep maximum.

“A common misconception is that heavy weights are required to stimulate muscular growth,” the UK researchers write, “but Carpinelli pointed out that this ‘heaver-is-better’ principle is simply unsubstantiated by research.”

Here’s the key point, as expressed by the researchers: “Perhaps the most important aspect of this is simply that to activate all the motor units within a muscle group, and thus recruit all the available muscle fibers to stimulate them to adapt to the training, it is not the %1RM that is the primary factor but rather the requirement to train to momentary muscular failure.”

In support, they cited three studies comparing training to momentary muscular effort and stopping short of failure. All three studies controlled for other variables, such as load, volume, and frequency. “Each study reported that training to momentary muscular failure produced significantly better results,” they write.

The researchers conclude: “The evidence suggests that individuals should be encouraged to train to momentary muscular failure, and this appears to maximize muscle fiber recruitment and, according to most research to date, will maximize gains in strength and power.”

As you’ll see, they are open to discussion of the superiority of particular rep ranges, but only in specified cases.

Load and Rep Range

The UK researchers recognize and summarize Dr. Ralph Carpinelli’s review study discussed here earlier; see Forget Heavy, Think Effort (link below). They chose not to replicate his work, but rather to recognize his efforts, and recommend reading of his article.

“As previously stated by Carpinelli,” they write, “the research suggests that it is not the load lifted that determines fiber recruitment, but fatigue of the lower threshold motor-units resulting in a sequential recruitment of higher threshold motor units through continued repetitions.”

Continuing, they add: “Research has considered ranges from 2RM through 100-150RM and found no significant difference in strength improvements between the results [5 studies cited], with only one exception.” 

In plain language, effort—not load or rep range—is the key variable in building muscle and strength. Resistance is largely a matter of personal preference. As Carpinelli wrote, “If a maximal—or near maximal—effort is applied at the end of a set of repetitions, the evidence strongly suggests that the different external forces produced with different amounts of resistance elicit similar outcomes.”

Pick your rep range, 2 to 20; it makes little difference—as long as you exert maximum effort in the final reps. Very high reps, over 20, may involve fatigue factors not conducive to gains in size and strength.

The researchers note that the 2009 position stand of the American College of Sports Medicine (ACSM) claims that maximal strength gains are obtained with loads of between 1 and 6 repetitions. They, however add: “It is apparent from the above data as well as recent comprehensive reviews of the literature that the research findings to date do not support the ACSM’s conclusion.”

Nevertheless, they call for more research in at least two areas. The first is lifting to increase bone mineral density (BMD).

“Research appears to suggest that to increase BMD training loads need to be 80%1RM,” they write. One study compared training at 50%1RM (~13reps) to training at 80%1RM (~8reps). “Whilst they reported almost identical strength gains, the higher load group produced significantly greater increases in BMD.”

The second area in which they believe further research may be called for is lifters with a predominance of slow- or fast-twitch muscle fibers. It appears that there may be more favorable rep ranges for these individuals. “For example, Jones suggested that persons dominant in fast twitch muscle fibers might obtain better results performing fewer repetitions with greater resistance, whilst persons dominant in slower twitch fiber-type might obtain better results performing a greater number of repetitions and lighter resistance.” 

That’s a logical assumption. As noted earlier, participants with a higher percentage of fast-twitch muscle fibers are able to perform fewer reps with a given percentage of 1RM than those with a lower percentage of fast-twitch fibers (and more slow-twitch fibers). 

The researchers believe this hypothesis may warrant further exploration.  It’s important to remember, however, that most people have a roughly equal distribution of fast and slow fibers. Further research would affect only those with a predominance of strength or endurance fibers. This would include most competitive power lifters and Olympic weightlifters on one extreme, and elite endurance athletes on the other.

Muscular Endurance

Conventional wisdom says that high reps are best for building muscular endurance. Is that true?

The ACSM says, Yes; when training for muscular endurance, use light to moderate loads (40-60% 1RM) and perform high repetitions, over 15.

The UK researchers, however, say there appears to be little support for the ACSM position.

Only one study supported the ACSM stand—20-28 reps produced more muscular endurance than 3-5 or 9-11 reps—while other studies “do not support the hypothesis that higher repetition schemes are more effective in increasing muscular endurance.”

For example, one study examined the effect of three different training protocols on muscular endurance: low reps (3 sets of 6-8 RM), medium reps (2 sets of 30-40 RM), and high reps (1 set of 100-150 RM). “No significant between-group differences in improvements in muscular endurance were found.” Another study compared 3 sets of 6-8 RM, 2 sets of 15-20 RM, and 1 set of 30-40 RM. “Again, no significant between-group post-test differences in muscular endurance were found.”

In short, research does not clearly support the proposition that high reps are best for building muscular resistance. If anything, the preponderance of the evidence supports the conclusion that more strength means more muscular endurance. That's where the UK researchers leave the issue.

I’m sticking with 2 to 20 reps. More muscular strength means more strength reserve and more muscular endurance. A person who can bench press 300 pounds can almost always do more push ups than the person weighing the same who can only bench 200.

Now, let’s turn to a related issue: how strength training can best be use to improve athletic performance. Conventional wisdom, once again, comes up wanting. You might say it strikes out.

The Issue of Specificity

It might seem logical to assume that swinging a heavy golf club or heavy baseball bat would improve performance—but you'd be wrong. In fact, it is more likely to slow down your swing, hurting performance. Strength training does improve performance—that’s why it is used in practically all sports—but only if it is used properly.

“There is no evidence that skill development is aided by performance of resistance exercises that bear some superficial resemblance to skills on the sports field,” the UK researchers report. “Not only is the transfer between superficially similar motor tasks quite low, but the performance of tasks that are similar (but not identical) to those used in actual performance can lead to negative transfer and concomitant decrease in performance.”

For example, the researchers cite a study that found the use of a weighted baseball bat for practice actually reduced the velocity of the swing when using the normal weighted bat. “This is hardly surprising as it is impossible to swing a heavily weighted bat as fast as a normal bat,” they write, “and therefore by slowing the movement down in this manner the athlete is effectively learning to swing the bat more slowly, and will change the mechanics of the swing accordingly.”

The same applies to the now common practice of lifting weights while standing on an irregular or moving surface. “It seems that instead of focusing an exercise on a muscle, many have succumbed to the concept of attempting that movement whilst challenging their balance,” the researchers write. “This often results in decreased force production due to instability.” Simply put, it makes the resistance training less effective—and does not improve general performance.

Balance is apparently a nontransferable skill. “Performing resistance exercises on unstable equipment will make an individual more proficient at performing resistance exercises on unstable equipment, but may not enhance the performance of sport skills,” an authority cited by the researchers wrote.

Building strength with resistance training does, in fact, improve athletic performance. But the focus must be on the muscle, not on balance or mimicking sport specific movements.

Here’s the bottom line from the UK researchers: “The use of resistance training for enhanced function and sporting performance should be based on muscular strength adaptations, and not on neuromuscular patterns including balance, which shows no transference.”

 *  *  *

Resistance training makes us stronger, and that’s what it should be used for. Stick to the standard exercises, such as the squat, deadlift, row, pulldown, bench press, incline press, shoulder press, sit-ups, and sidebends. Do that—with effort—and you’ll be stronger, faster, more muscular, more enduring, and healthier.

You’ll be better in just about any physical activity you choose, as long as you also practice that activity.

See also our new article on cross training:  GO

We promised links to our previous articles on effort-based training; here they are: Forget Heavy, Think Effort http://www.cbass.com/Carpinelli.htm and Lifting—Many Ways that Work http://www.cbass.com/LiftingWithEffort.htm

[To read the entire UK study, go to http://www.medicinasportiva.pl/new/pliki/ms_2011_03_08_Fisher.pdf . For an opposing view from a blogger, see http://trainingscience.net/?page_id=174 ]

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