Power Training Increases Force of Contraction WITHOUT eliciting Structural Changes in the Muscle

This should not come off as a news flash for you guys but today we are going to share a study I recently browsed upon which proved how power training increased force of contraction and Jumping performance but doing very little in terms of eliciting any sort of changes in muscle structure whatsoever.

randy barnes specialized shotput training


This means that power training increased performance without changing the muscle structure – or at least the authors were not able to detect this change. This proves the principle of training specificity and SAID (specific adaptation to imposed demand) that we were talking about in our past article and how training for performance should be built upon eliciting improvements on performance without expecting too much or any hypertrophy at all.

This also means that muscles don’t necessarily have to be big in order to elicit greater force of contraction. Muscle surface area however will help a little but power gains are but a side effect of increased muscle mass and does not directly cause increase in velocity of contraction.

However in this study, the authors also measured if they will come across any changes in the muscle fibre compositions during the ten week long experiment. The authors regularly took muscle biopsies from the subjects but after ten weeks of study they found no statistical difference at all:

The results of the present study demonstrated that maximal voluntary isometric contractions of Knee Extensor muscles did not change during the training period, while plantar flexor muscles produced higher forces after 10 weeks of training. The maximal rate of force development of Knee Extensor increased, however, significantly during the first 10 weeks of training. In the drop jumps, the increase in the rising height of the center of gravity were highly related with the changes in the knee power but only non-significant changes were observed in EMGs during the training. The mean percentage for Myosin heavy chain and titin isoforms, muscle fiber distributions, and muscle fiber areas were unchanged.

Here’s the table that indicate the results of the muscle structure analyses, now you tell me if there’s any difference:



It is important to state that this study used trained individuals or “Recreationally Active Individuals” as how they put it in the paper. Here’s the abstract of the study (Full Text here):

Effects of power training on muscle structure and neuromuscular performance
Kyröläinen H1, Avela J, McBride JM, Koskinen S, Andersen JL, Sipilä S, Takala TE, Komi PV.


The present study examines changes in muscle structure and neuromuscular performance induced by 15 weeks of power training with explosive muscle actions. Twenty-three subjects, including 10 controls, volunteered for the study. Muscle biopsies were obtained from the gastrocnemius muscle before and after the training period, while maximal voluntary isometric contractions (MVC) and drop jump tests were performed once every fifth week. No statistically significant improvements in MVC of the knee extensor (KE) and plantarflexor muscles were observed during the training period. However, the maximal rate of force development (RFD) of KE increased from 18,836+/-4282 to 25,443+/-8897 N (P<0.05) during the first 10 weeks of training.

In addition, vertical jump height (vertical rise of the center of body mass) in the drop jump (editor’s note: Dtest increased significantly (P<0.01). Simultaneously, explosive force production of Knee Extensor muscles measured as knee moment and power increased significantly; however, there was no significant change (P>0.05) in muscle activity (electromyography) of Knee Extensor muscles. The mean percentage for myosin heavy chain and titin isoforms, muscle fiber-type distributions and areas were unchanged. The enhanced performance in jumping as a result of power training can be explained, in part, by some modification in the joint control strategy and/or increased rate of force development capabilities of the Knee Extensor muscles.

Now let’s take a look at their training protocol:


The experimental group trained twice a week for 15 weeks, which was preceded by a 2-week preparatory phase consisting of light loads of squats, deadlifts, as well as abdominal and calf exercises. Each training session was controlled by an experienced supervisor. The training of leg extensor muscles included various types of stretch-shortening cycle (SSC) exercises such as jumping performances with a special sledge apparatus, drop jumps from the heights of 20–70 cm, jump squats (30–60% of one repetition maximum), one leg and two leg hopping, and hurdle jumps. The jumping performances (five to 10 repetitions per set) were performed with a maximal effort to develop explosive force production of lower limb muscles. The overall number of muscle actions increased progressively from 80 to 180 actions per training session throughout the whole training period. Training diaries of the subjects revealed that other physical activities such as cycling, walking, and ball games lasted almost 6 h per week for the experimental group and 4 h 30 min per week for the control group (Po0.27 between the groups). However, this extra training was their normal weekly activity, and it did not change during the experimental period.

As we can all see these are all great jump-training exercises. Those explosive moves (especially the drop jump or depth jumps) are indeed very effective in training for explosiveness but do very little in terms of muscle hypertrophy and as this study found out did little to none in terms of muscle structure change and there was even no difference in regards to EMG muscle activity.

The authors also think that it is possible that the parameters they used to measure muscular structure change weren’t sufficient to show the change if there’s any:

The present study confirms that mixed strength training methods could affect more clearly neuromuscular performance and its explanatory mechanisms than power training alone as Newton et al. (2002) and Lyttle et al. (1996) have demonstrated. Thus, future training studies should focus on developing new parameters besides the conventionally employed MVC and RFD. More detailed analysis of motor unit firing patterns in combination with attempts to clarify modification in the fine structure of the contractile and elastic muscle components may be the way to find true mechanismic explanations.

Another important detail that we should not take for granted is that the subjects ceased to make any further progress in power beyond 5 weeks. The authors concluded that the current stimulus that the experiment provided has no longer been sufficient to produce further gains and the subjects have adapted or “outgrew” the current protocol. This further demonstrates the principle (see Grand-Daddy Principles or SEVEN COMMANDMENTS) of “overload” and “GAS” (General adaptation syndrome) – at this point it would have required another level of overload to illicit further OVERCOMPENSATION (again, see the article about the 7 commandments if you don’t know what Overcompensation is) from the subjects.

However, during the last 5 weeks no additional increases in EMGs or force were observed. This may be due to too small or too similar training stimuli or overreached adaptation processes. In other words, the present subjects reached their limit in improving their neuromuscular performance with the power-only training protocol utilized in this investigation

Subtle improvements in many areas create the package

Another point that can be raised is that improvements in explosiveness, power, performance and athleticism cannot be caused simply by a specific change in “fine” muscular structure; there are many factors that play here including neuromuscular adaptability, form, etc. and some changes may be subtle but the point is that the progress in this regard is due to gains in many small aspects and many seemingly insignificant changes that work together to create measurable boost in performance. In other words what counts is the “total package” as what the authors speculate:

Although all EMG changes were statistically insignificant, their combined effect may explain increased joint power around the knee joint. (Bear in mind that this is NOT a scientific conclusion but a speculation in part of the authors – and it indeed makes sense)

So bodybuilders can train specifically for muscular hypertrophy using methods that are proven to elicit that certain response and could show specific muscular changes that justify their gains. Athletes however can train for explosiveness and successfully improve their muscles’ functionality but will show very little to no specific muscular-structure change that will singlehandedly explain their gains.

There may or may not be a specific parameter that can be measured with regards to muscle structure to explain gains in muscle contractile force. In the future there may be a way to determine if there is a specific muscle structure change that brings about increased explosiveness but maybe the authors are correct and we may be looking in the wrong places to find the specific cause of that specific effect – maybe muscle structure change is not where we need to look into or maybe we just need to look for new parameters.

However only one thing is for sure: Explosiveness training works! If you want to read our posts about increasing vertical jump, go here. Here are or other articles that talk about explosiveness training. Eat your eggs, A-lifters!

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