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Science of Sport: What Intensities Should You Be Using For Your Strength Training?

A Range Of RMs May Actually Be Optimal

In past e-newsletters I have described the merits of three- vs. one-set strength training and the value of conducting strength training three times a week. In this issue, I would like to address an important question: What load (intensity) should you utilize when you carry out your running-specific strength-training movements?

Research has provided some mixed messages on this matter, but a general consensus in the scientific community, as expressed in a review written by Matthew Feigenbaum (at right) and Mike Pollock, is that the use of loads from 4 to 8RM produces the greatest gains in strength (1). As you know, 4RM refers to a load or resistance with which an assigned movement can be completed successfully four times prior to exhaustion (naturally, the same movement could be completed one, two, or three times as well, but not five times). 8RM is a still-tough but lighter load - a resistance against which a movement can be finished eight times before failure occurs.

The use of loads which are lighter than 8RM (and therefore the performance of sets with lots of reps) is often thought to improve endurance rather than strength (2). For example, one common recommendation made to endurance runners involves the utilization of fairly lenient loads of 12 to 20RM. However, the type of endurance which is gained during such fairly facile lifting is seldom specified. Is it fortitude while chewing on a stalk of celery? Is it persistence which displays itself only during the chosen strength-training exercise - or in all other movements which rely on the same muscles, even if those movements are functionally different?

Of course, the ultimate question is: Can 12 to 20RM actually promote endurance during competitive running? The naysayers like to point out that a set of 12 reps with a load of 12RM seldom takes more than 15 to 20 seconds to complete (depending on the actual movement). Could such brief durations of effort directly expand endurance in a 5-K race lasting 20 minutes (in other words, during an exertion which is 60 to 80 times as long as the selected set of reps)? It does not seem very likely.

The idea that loads of 4 to 8RM produce the greatest gains in strength can also be called into question. Are we really convinced, for example, that 3 sets of 8 reps at 8RM would be better for strength improvement than 8 sets of 3 reps at 3RM?

If we discovered that 8 sets of 3 reps at 3RM were superior, a problem in interpretation would be that much-greater weight would be used in the 24 reps of 3RM lifting, compared with the 24 reps of 8RM work (after all, a 3RM resistance is greater than 8RM). We could reduce the number of sets at 3RM to make total load equivalent between the strategies, but we would still face differences in speed of movement which would cloud the conclusions we would draw (the 8RM motions would probably be quicker). Trying to get to the bottom of the question about optimal load is a little like attempting to dig a very nice hole at the beach - only to find that the sides of the cavity keep caving in.

As Robin Judice (CSCS) and Karen Ward (CPT) point out, the difficulties associated with finding the right load are eased when one considers the time, risk, and timing factors associated with strength training (3). In other words, using loads as heavy as 1-, 2-, or 3RM tends to create a need for longer recovery times between sets, compared with lighter loads; thus, they may represent an inefficient use of time for athletes who do not have all day to train. There is also greater risk of injury when heavier intensities are utilized, especially if you are a relatively inexperienced strength-trainer. True, some risk is also present with lighter loads such as 8RM, but an athlete using such an intensity usually gets an inkling that he/she is becoming weak or unstable during the reps and can stop the set early, if necessary, without having to get rid of a very challenging weight. Finally, a timing factor also needs to be considered. It is probably not optimal to conduct 3RM exercise just before a quality running workout, because of the ample shadow of fatigue which can drape the ensuing running effort in lethargy. In addition, 3RM work usually does not work very well after a good run, because the leg muscles are often too fatigued from the quality running to handle the heavy weight. It is much easier to blend lighter-RM work with running training, especially when one is hoping to carry out three strength sessions each week.

At the other end of the load spectrum, the effects of lower-resistance, 8- to 20RM strength training on running performance have never been carefully compared with the benefits of 4- to 8RM work. The former, lighter loads could be very productive for runners, not because they enhance "endurance", as is often stated, but rather because speed of movement can be increased when lighter resistance is utilized. Specifically, the movement velocities can more closely mimic those associated with real-live running, and thus the transfer of strength from the resistance training to running may actually be greater.

We may well learn, in the future, that blending 4- to 8RM work with less-lofty loads (12 to 20RM, for example) provides an optimal combination of strengthening exertion for runners, because such commingling advances both strength and velocity of movement, thus leading to peak upgrades in running power. Power optimization (covering a fixed distance in a shorter period of time), of course, is the ultimate goal of the competitive runner.

References
(1) "Strength Training: Rationale for Current Guidelines for Adult Fitness Programs," The Physician and Sportsmedicine, Vol. 25 (2), pp. 44-64, 1997

(2) Designing Resistance Training Programs. Champaign, Illinois. Human Kinetics, 1987

(3) Personal communications

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