Study Design

In the study, the researchers compared a concentric-only bench press and squat to one done with a counter-movement to see where peak power was achieved. While a counter-movement can be done with a few different techniques, this one was simply done with a full eccentric component to start the lift. As such, the counter-movement versions of the lifts looked like how you might normally do them in the gym.

The participants were 27 men with an average of over six years experience in squats and bench presses. They each performed the squat and bench press with various loads, sometimes using a counter-movement and sometimes just using the concentric phase of each exercise, while the researchers measured their power outputs.

In both exercises, maximal power was achieved at a lower weight with the counter-movement. With the bench press, maximum power was achieved at about fifty percent of one-rep-max when using the counter-movement, as compared to about sixty percent with the concentric bench press. For squats, the maximum power was achieved at higher levels, reaching seventy percent of one-rep-max for the counter-movement and eighty percent without.

Interestingly, and perhaps surprisingly, the max power outputs occurred at different weights, but were roughly the same. So while more weight was needed for the concentric-only lifts to achieve maximal power, the maximum level of power reached was the same as it was with the counter-movement.

The Role of the Stretch Shortening Cycle

The lower weight required to reach maximum power with the counter-movement is perhaps a result of the limit in the elastic loading effect of the stretch shortening cycle (SSC). The SSC help the body makes muscle action more efficient. As a muscle elongates, it stores up energy that it can then use to generate more power when it’s time to act. This is why you can jump higher if you drop quickly first, or punch harder if you draw your hand back first.

The SSC has been shown to have load limits. The researchers noted that as weight increases, the motion is slowed and energy storage is reduced. This suggests that if power production is the most important aspect of training, as it would be for many sports, the lighter weights used in this study may be optimal.

Some further points might be useful for lifters, however. Heavier loads, while not optimal for peak power development, might still be good for maximal strength development. When using a load corresponding to eighty percent of maximal force, it took the lifters four times longer to reach peak power output during a single lift. This delay was due to the effects of SSC. SSC typically enhances power at the start of the move, but if your sticking point is mid-lift, a heavier load with a counter-movement might be just what the strength and conditioning coach ordered.

Not only was the effect delayed during the lift, but heavier loads also prolonged the effect of the SSC. This means that the effect wasn’t as sharp, but it lasted longer throughout the lift. Once again, a heavier load may be beneficial for developing power later in a lift.

Conclusions

Peak power was similar even without the counter-movement, and concentric-only lifts were shown to be easier to recover from than lifts that included eccentric components. These results suggests concentric-only power development could be a promising method for the future.

References:

1. Erika Zemkova, et. al., “Enhancement of Peak and Mean Power in Concentric Phase of Resistance Exercises,” Journal of Strength and Conditioning Research, DOI: 10.1519/JSC.0000000000000517

Photo courtesy of CrossFit Impulse.

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Great, let’s all train for power. However, to do that we need to know just what power is, and that’s aim of this article.

How Hard Are You Working?

We know that when we push or pull against an object we’re applying a force (if you don’t know this, see my article on force-time curves), and if we push or pull hard enough the object will move, in accordance with Newton’s first law of motion. When the object you’re applying force to moves in the same direction, you’re performing work – the product of force and distance.

This is very useful, because, like impulse, work adds greater detail to any description of the mechanical characteristics of a movement by combining effort (force) with outcome (displacement). We can get a pretty good idea of how much work is been performed by first estimating the force applied to the mass and then multiplying it by the distance that it travels.

A Lifting Based Example – The Deadlift

If you load a barbell up to 200 kg and your deadlift range of motion is 50 cm, the vertical work that you perform can be calculated like so:

Force = 200 (barbell mass) × 9.81 (acceleration of gravity) = 1, 962 N

Then multiply this by the distance you lift the barbell:

1, 962 × 0.50 (meters) = 981 J (joules) of work

Pretty simple, right? However, we must remember that other work was performed during this lift. For example, work was performed to move our body’s center of mass. However, unless you have access to the sort of kit that’s typically only found in well-equipped biomechanics laboratories you won’t be able to measure this. For those of you who are interested, Dr. John Garhammer provides a range of examples in his excellent review of power measurement (see the reference list at the end of this article).

If we we’re feeling ambitious, we can take the example of the vertical jumper from the force-time curves article and calculate the work he performed like so:

Jumper weight (force) = 787 N × 0.27 m (his jump height) = 212.5 J

Quite a difference, and this is where power comes in.

What About Energy?

But hang on, what about energy? Mechanical energy can be defined as the capacity to perform mechanical work. Humans possess mechanical energy, and this is typically found in the form of either potential energy or kinetic energy, where the former can be simplified as existing as a consequence of position:

Potential energy = mass × acceleration of gravity × height (or distance)

And the latter can be simplified as existing as a consequence of motion:

Kinetic energy = mass × velocity² ÷ 2

This gives us a little more information, but means that we need some way of measuring how quickly the mass we’re interested in is moving. It also highlights that what we’ve been able to calculate so far is actually an estimate that can be made using the relatively little information we have. Ideally, we’d have a record of either motion or force (or both) recorded over known time intervals to obtain accurate records of work, energy or power. (Page 97 of Drechsler’s Encyclopedia of Weightlifting provides a relatively simple way this can be done.)

Interestingly, at the top of the vertical jump our jumper has potential energy:

Potential energy = mass (80 kg – ish) × acceleration of gravity (9.81) × height (0.27) = 212 J

Which should look familiar (see above), but he has no kinetic energy:

Kinetic energy = mass (80 kg – ish) × velocity² (0 – top of the jump) ÷ 2 = 0

Which shouldn’t come as a surprise! If we were to calculate the kinetic energy of our jumper at take off, though, it would be much more than 0:

Kinetic energy = mass (80 kg – ish) × velocity² (2.31 m/s at takeoff) = 5.34 ÷ 2 = 213.4 J

This number is starting to look familiar (give or take a few joules). So, we perform work by applying a force to a mass to move it. We do this and our capacity to perform work changes. Pretty simple.

The Definition of Power

Now we get to the fun bit – power. What is it? Power is simply the rate at which we perform work. So, it’s a combination of force and how quickly we can move something in a given direction, which is also known as velocity (think back to my first article). Therefore, power can be calculated in one of two ways:

Power = work ÷ time or Power = force × velocity

Why Is Power So Important?

To illustrate its importance let’s think back to the two examples we used earlier. (However, I’d once again recommend you find a copy of Garhammer’s paper for other examples, and a classic lifting-related example comparing deadlift and clean work and power can also be found in Dr, Pat O’Shea’s book: Quantum Strength Fitness II.)

Now, if you have a 300 kg deadlift the 200 kg lift we discussed earlier would represent about 67% of this one repetition maximum (1 RM), which means that you could probably lift it relatively quickly, in about 1.5 seconds. Therefore, an estimate of average power applied to the barbell could be obtained like so:

Force = (1, 962 – see above) × velocity (0.50 m ÷ 1.5 s = 0.33 (ish)) = 647 W (watts)

Of course, the heavier the lift, relatively to your 1RM, the longer it’s going to take to complete. The longer the lift takes to complete the less power you’ll be applying to the bar.

This demonstrates the simplest way to train power – train strength. Get stronger and you’ll be able to lift the same amount of weight (say 200 kg) faster. You’ll need to apply the same amount of (average) force, but velocity should be greater because you’re able to lift more quickly.

Of course, once you’ve saturated the whole ‘getting stronger’ thing there are other methods that can be used, some of which have been discussed on Breaking Muscle, and some that I’ll try and touch on in future articles.

Where Do You Stand?

Finally, let’s consider a simple method that will let you figure out where you stand. You can measure your vertical jump quite easily, and if you do this you can get a pretty good estimation of your peak power output by doing some simple math. You could obtain jump height from video footage (from your phone for example – see reference to Drechsler above) and, if you know how many frames it records per second, calculate ‘flight time’ – the time you spend in the air. Jump height can then be recorded like so:

Jump height = (flight time² × 9.81) ÷ 8

An even easier way of recording jump height can be found here – an excellent resource that also provides ‘power calculators’ toward the middle of this page. Of all of these I would recommend using the ‘Sayer’s Equation.’

So there, you have it. Power is the product of how quickly something moves when we push or pull it, and has obvious implications for sports performance. This, of course, is why such a big deal is made about it, and it’s something I’d like to go into more detail with in future articles.

References:

1. Baker, Daniel. “Differences in strength and power among junior-high, senior-high, college-aged, and elite professional rugby players.” Journal of Strength and Conditioning Research 16, no. 4 (2002): 581-585.

2. Drechsler, Arthur. The Weightlifting Encyclopedia: A Guide to World Class Performance. Flushing, NY: A is A Communications, 1998.

3. Garhammer, John. “A review of power output studies of Olympic and Powerlifting: Methodology, performance prediction, and evaluation tests.” Journal of Strength and Conditioning Research 7, no. 2 (1993): 76-89.

4. O’Shea, Patrick. Quantum Strength Fitness II (Gaining the Winning Edge). Patrick’s Books, 2000.

Photos courtesy of Shutterstock.

The post Power: What It Is, Why We Want It, and How We Generate It appeared first on Breaking Muscle.

Because the vertical jump is a standard measuring stick, it is an often-researched topic. Recently two studies were conducted to determine how the vertical jump was affected by 1) strength and power training and 2) training on stable versus unstable surfaces.

The first study compared the effects of strength training (ST) and power training (PT) scripts on neuromuscular adaptation and alterations in vertical jump performance, as well as kinetic and kinematic factors (study of motion and the description of motion, respectively). The subjects were forty physically active men (average height: 5’-10”, weight: 165 pounds, and age: 23.5 years). Each subject had at least two years of strength training experience and was assigned to one of three groups: ST, PT, or a control (C) group. Maximum dynamic and isometric strength, cross-sectional area, and muscle activation were assessed pre- and post-test. Additionally, squat jump and countermovement jump performance, kinetic, and kinematic factors were also assessed.

Conclusions of the study:

• Maximum dynamic strength increases were statistically similar for the ST (22.8%) and PT (16.6%) groups.
• Maximum voluntary isometric contraction increases were similar the ST and PT groups.
• There were no changes in muscle activation, although a main time effect for muscle fiber cross-sectional area occurred.
• Static jump height increased following ST and PT due to the faster concentric (raising) phase and a higher rate of force development.
• Countermovement jump height increased only following PT, but no significant kinetic and kinematic changes were evident.

Take home message of study one: ST and PT are equally effective in increasing strength gains, neuromuscular adaptations, changes in jumping movement pattern, and static jump performance. Neither ST nor PT were able to affect the static jump and the countermovement jump movement timing and joint extension sequencing initiation. Therefore, become stronger generally, work on power activities generally, and practice being explosive with exact activity-specific drills.

The second study compared power outputs in the concentric (raising) phase of squats performed in interval mode on stable and unstable surfaces, respectively. The subjects were sixteen physical education students who randomly performed six sets of eight repetitions of squats on a 1) stable support base and 2) BOSU (unstable) ball, respectively, on different days with a two-minute rest between sets. A 1-repetition maximum (1RM) was obtained for each subject. Repetitions with 70% of the 1RM were then performed under both conditions. Using a computer system, force and velocity were calculated to determine power output.

Not surprising, results showed significantly lower power outputs when squats were performed on an unstable surface as compared to a stable support base. In the initial set, mean power in the concentric phase decreased more with the unstable surface compared to the stable surface during the squats (10.3 and 7.2%, respectively). In the last set, the mean power reduction resulted in nosignificant differences between the BOSU ball and the stable surface (11.4 and 9.6%, respectively).

Conclusion of the study: Power output during resistance exercises is more significantly compromised when using unstable surfaces as compared to stable conditions. If instability resistance exercises are used in a training program, understand maximal force production will not be realized.

My recommendations based on the results of these studies:

1. To improve leg power, use resistance training to increase strength.
2. Perform strengthening exercises on stable surfaces to maximize force output.

References:

1. Lamas, L; Ugrinowitsch, C; Rodacki, A; Pereira, G; Mattos, E.C.; Kohn, A.F., and V. Tricoli, “Effects of Strength and Power Training on Neuromuscular Adaptations and Jumping Movement Pattern and Performance,” Journal of Strength and Conditioning Research 12 (2012): 3335-3344.

2. Zemková, Erika; Jele?, Michal; Ková?iková, Zuzana; Ollé, Gábor; Vilman, Tomáš, and Hamar, Dušan, “Power Outputs in the Concentric Phase of Resistance Exercises Performed in the Interval Mode on Stable and Unstable Surfaces.” Journal of Strength & Conditioning Research 26 (2012): 3230–3236.

Photos courtesy of Shutterstock.

The post Vertical Jump Performance: The Effects of Strength, Power, and Training Surface Stability appeared first on Breaking Muscle.