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Strength training in volleyball: Periodization and other issues

Professional volleyball is becoming more and more demanding from a physical standpoint. The number of competitions is increasing and elite players are involved in those all-year-round. In fact, players involved in club championships and national team tournaments play a very high number of matches and have very few rest periods during the year. We could say that the sporting season for those individuals is never-ending. If we also consider top clubs, we can easily see that during the last years the number of matches increased. This is due to the fact that top teams are not only involved in playing the national championship, but also in national and European cups. This increased demand is of course changing the way physical conditioning was done before. Nowadays there is a need for a correct planning of the activities, travels and rest periods in order to be able to avoid overuse injuries, overtraning and underperformance. The key for being able to prevent all of the above is a very well planned periodization, which needs to be monitored on a weekly basis and corrected during the season. Before planning any type of program it is important to be aware what are the physical demands of the game. Some players play different positions and so have different needs (i.e. Libero, Setter and Opposite). Then, it is important to establish individual characteristics (and performance level). In this connection it should be pointed that appropriate tests should be utilised in order to gain information which could be useful in the development of the training program itself. The training programme should then be individualised based upon each player’s individual characteristics.

The periodization plan has to take into account the official and friendly matches, the rest periods and the total number of training sessions.

Strength training sessions can be planned during the competitive season if a proper work-to-rest planning is performed. Testing and training monitoring is extremely important, since it is the only way to determine adaptations and prevent overtraining syndrome or underperformance. By controlling adaptations we are in fact able to re-evaluate athletes’ level of performance and then we can change the training methodology, the exercises and the program itself and be able to have further improvements.

With this in mind, before coming to some practical examples, it is important to re-consider some of the concepts behind periodization.

Strength training, periodization and volleyball

Strength training should be implemented in volleyball not only to improve jumping ability and spiking velocity. Volleyball performance is characterised also by the ability to maintain a good balanced position when receiving and passing the ball, performing a dig or a block and sustaining the impact of fast balls with the upper body. Strength training should be then directed and focused not only on the lower limbs but also on the upper limbs and the trunk most of all to avoid injuries, but also with the view of improving some specific technical skills.

Most of the research studies published in the literature have been carried out using physical educations students, untrained people or recreational players, and we all know that training an elite athlete is a different issue. The higher the level of the athlete, the more difficult is produce enhancement of performance. However, the principles presented in this blog article could be extended to all type of volleyball players.

Before discussing periodization, it is important to remind what are the effects of strength training exercises. The adaptation to the training stimulus is related to the modification induced by the repetition of daily exercise, and is specific for the movement executed (Edington and Edgerton, 1976). These adaptations are related to the fact that human skeletal muscle is a specialized tissue which modifies its overall function capacity in response to chronic exercise with high loads (McDonagh and Davies, 1984). The above mentioned findings all suggest that resistance exercise can be an effective means for enhancing neuromuscular performance. In this connection it should be noticed that changes within the muscle itself constitute the most important adaptation to resistance exercise (Sale, 1988; Behm, 1995). In fact, strength training response has been shown to be mediated by both neurogenic and myogenic factors (Moritani and De Vries, 1979). Neural adaptations have been indicated as the first changes occurring in the muscle, permitting gains in muscle strength and power in the early stages of a resistance exercise program in the absence of increase in cross-sectional area of the muscle (Behm, 1995; Costill et al. 1979; Sale, 1988). It has been also demonstrated that specific adaptations occur depending on the training program implemented (Sale and Mc Dougall, 1981). Strength training then, can be considered a training stimulus which produces specific adaptations on human skeletal muscles, based upon the protocol utilized for training. The specificity effect of strength training has been underlined by many authors (Sale, 1988; Behm, 1995; Morrisey et al. 1995; Bandy et al. 1990) and the velocity specificity effect has been suggested as one of the most interesting outcome of resistance exercise programs. However, even if the mechanisms underlining this velocity-specificity effect have not been clearly defined, most importance has been given to neural adaptations such as improved coordination, increased activation of prime movers muscles (Moritani and De Vries, 1979) recruitment and synchronization.

It appears then clear that with strength training the neuromuscular system is able to perform to a higher level. It is also clear that several neurological mechanisms are involved in the early gains, with hypertrophy being the last step of the adaptations process. Strength training impacts several systems, in fact endocrine, skeletal, metabolic, immune, neural and respiratory acute and chronic responses have been observed following single bouts or repeated bouts of strength training.

With this in mind we have then to say that the careful selection of the training variables (volume, intensity, density and exercises) determines the effectiveness of the program. Exercises should be chosen based upon the possibility of transfer in competition-specific motions. The parameters to control such outcome are very simple: muscle-joint mechanics and muscular activation timing.

Let’s consider the first one. In volleyball one of the most important actions is the volleyball spike. This technical motion is performed with a stretch-shortening cycle of the leg’s extensors muscles. We know the muscles involved in such motion and we know the mechanics (stretch-shortening cycle). We also know that this motion is a closed chain-type of activity. Hence, when choosing the exercises the movement patterns should mostly be characterised by closed-chain-type of activities which simulate similar mechanics.

Let’s now consider another aspect: timing of muscle activation. The jump and spike action in volleyball, depending upon the technique utilised, is performed with lower limbs muscles performing mechanical work for a duration ranging from 300 to 450 milliseconds (Bosco, 1985; Coutts, 1982; Viitasalo, 1982). Similar times were also measured in 1 legged spike actions Huang et al. (1999). Specific exercises should also be included in the training plan repeating timing and patterns of activation.

Now then, we know that general strength training is good for enhancing neuromuscular performance and that adaptations are stimulus-specific. We also know that the specific performance demands are related to the capability of an athlete to express maximal power in limited amount of time.

Let’s now discuss periodization in elite volleyball. It is important to say that the earlier model developed by Matveyev and presented in most books of training methodology should be considered only as a pedagogical model, and not as a real model to be based on. Most of all, it should be pointed that most of the periodization models have been developed for individual sports and cyclic activities (running, rowing, cycling) and there is at the moment no model available for team sports demands. So, we should re-consider all the information which is available on this topic. From a pedagogical standpoint some concepts of periodization are important.

It is in fact the definition of specific work to rest ratios, volume undulations, and intensity undulations, that defines effective training cycles. However it should be pointed out that what is good for a team cannot be good for another one, since there are different individuals and different athletic levels. This means quite frankly that it is impossible to have an “optimal model”. There are however general concepts which are useful for developing an effective periodization model.

In most American books periodization is divided into 3 phases: preparatory, competitive and transition phase. We know that nowadays top volleyball players have a very long competitive season and a very short preparatory and transition phases. Lower level players of course have the luxury of time and could spend more time in preparation and/or transition. If we look at the typical playing patterns of international players and the typical club and national team calendar of elite European nations we can see how some players move from Club activity to an intense summer of International activity to then start again in the Club with minimal time for recovery and almost no time to train before getting involved in further competitions.

In many books an optimal progression is suggested for strength training: anatomical adaptation phase, hypertrophy phase, maximum strength phase, conversion phase and maintenance phase. Those concepts are of course based upon the structure of the sport season in USA where the competitive season is relatively short as compared to Europe and there is a lot of time for preparing the season itself, with almost no time during the competitions.

I take the liberty to state that this approach is wrong in European sporting seasons in most team sports. For sure, be able to go through all of the above mentioned phases, we should have enough time. We all know there is no time (and this is not a bad thing sometimes…). Hence, the solution is a different approach to strength training.

In this approach approach, maximal dynamic and explosive-type loads have to be used concurrently, in order to gain force and power at same time. Of course a good planning should change during the season the percentage of volume dedicated to one or the other, but during the whole season both have to be trained. The key for understanding when and if it is time to change something in the training program is testing.

Adaptations to strength training programs depend on the type of muscular activation, intensity and volume (Sale & Mac Dougall, 1981; Atha, 1981). We know in fact that training strength utilising heavy loads and low contraction speed determine enhancement of maximal dynamic strength (Berger, 1962; Hakkinen, 1994). However, it is important to say that in order to produce enhancement in power and explosive-type motions, those loads have to be lifted with the highest possible speed and lighter loads have to be utilised as well (Berger, 1963; Hakkinen, 1994; Kaneko et al., 1983; Moritani et al. 1987). The combined methodology has been shown to be productive in enhancing a wider spectrum of the force/velocity capabilities of skeletal muscles (Harris et al., 2000; Newton & Kraemer, 1994; Stone, 1993; Stone et al. 1980).

The characteristics of the explosive-power exercises must be short duration (200-300msec) and high intensity. An example of the different activation patterns are presented in Figures 1 and 2. In this case a professional female volleyball player was performing half squat with 70% of 1RM and drop jumps from a box 40cm high starting with knee bent at 90°. Here it is possible to see the different EMG activity and the duration of the mechanical work. This is an example of the different timing and muscle activation patterns in different exercises. Again, this is a support of this “muscle tuning” approach to strength training. The aim is to permit to the neuromuscular system to express its maximum in a working time spectrum which is the characteristic of the performance demand. So, when choosing the exercises and developing a program, always there is a need of using combined exercises (maximal dynamic strength and explosive strength).

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Figure 1. Half Squat with 70% of 1RM load. Biomechanical Analysis

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Figure 2. Drop Jump. Biomechanical Analysis

Concluding remarks

It is impossible to have a specific model for planning a season in team sport. The periodization plan should take into account the level of the team, the competitions, the number of the players available, the travelling schedules and many other aspects. Most of the times, what is planned at the beginning needs to be changed, due to the results and participation to different competitions (European Cups, Play-offs…). It means that the only way to try not to make mistakes leading to overtraining or underperformance is to test routinely the players and adjust the programme allowing appropriate rest-to-work ratios. Of course it is important in the pre-competitive phase to increase the training volume to build up maximal dynamic strength mostly and endurance to the game throughout game-like drills. Then, it is possible to increase intensity, increase the amount of explosive-type exercises and put more emphasis on speed-strength drills. Rest is important, if your players have enough rest they will perform always well not only in competition but also when intense technical and tactical sessions are planned. Sometimes it is better allowing one or two days off rather then exaggerating with training sessions. One main rule: if the players are tired, the best training is rest and recovery!

In the following figures there are examples of the training load (always referred only to the strength training sessions) of professional female volleyball teams participating in various competitions. As you can see two teams with two different load distributions can still improve vertical jumping ability. In one case at a certain time of the season due to a high density of competitions, the training load was lowered to maintain the level reached and avoid overtraining. In the second case, a different approach was used since the goals and the characteristics of the team were different.

These are only examples of how to manage and plan the season. The most important aspect to remember is that without a proper testing and monitoring procedure you would never be able to understand if the plan is effective or not and most of all, in which direction adaptations are going (are the players gaining strength, power or both?). Without this approach, training becomes just a blind guess which is unlikely to produce performance gains.

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Figure 3. Training load and vertical jumping ability in a professional volleyball team participating in the Spanish League, Spanish Cup and European Champion’s League (average values n=10)

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Figure 4. Training load and vertical jumping ability in a professional volleyball team participating in the Italian League and Italian Cup (average values n=10)

Strength testing

Strength and Power measurements for strength training planning: what is out there?

It is well accepted that success in most sports depends on the ability of the athletes to exert high levels of strength and power (Stone et al., 1994). For this reason, training programs are nowadays directed to improve those two characteristics no matter what sport the athlete is preparing for. Technology in sport has quickly developed and nowadays many tools are availble to assess an athlete’s strength and power capabilities. Moreover, recent dynamometers provide a form of biofeedback to be able to guide the athlete during his/her strength training program just like heart rate monitors provide guidance during running, rowing and cycling sessions.
Before discussing how to measure strength and power and how to use those measurements to change an athlete’s training program, we need to review some very simple biomechanical concepts.
First of all, strength relates to the ability of an individual to produce force. Force is measured in Newtons (N) and is what is required to stop, start or alter motion. According to Newton’s 2nd law, Force can be calculated as follows:
F = m x a
Where m is the mass and a the acceleration.
Acceleration can be defined as the rate of change in velocity of an object and is calculated as follows:
a = Dv/Dt
Where v is velocity and t is time. Acceleration is measured in m/s2.
When an object experiences a change in position (displacement) it has been displaced and motion has occurred. Since motion has spatial and temporal elements it is important to know the speed and/or the velocity of the object. Specifically, speed defines how fast an object is moving whereas velocity tells both how fast and in what direction the object was moving.
Velocity is calculated as follows:
v= Ds/Dt
Where s is the distance travelled by the object and t is the time needed to cover the distance. Velocity and speed are measured in m/s.
In many short duration events (i.e. sprinting, vertical jump, Olympic lifts) the rate at which muscles can produce mechanical work is often the variable limiting performance. For this reason, knowing how much power an athlete is producing in a given motion could be important to assess the effectiveness of a training program. Power production is measured as the amount of work done per unit of time.
Since mechanical work is calculated as the product of the displacement experienced by an object and the component of force acting in the direction of its displacement divided by the time needed to complete the displacement, it can be calculated in the following ways:
F x s/Dt = F x v
Power is measured in watts (W).
All of the above parameters can be calculated as an average over a range of motion or as an instantaneous value occurring at a particular instant during the displacement of an object.
Enough biomechanics! Let’s start to use it to understand how many commercial systems are using biomechanics to measure Force, Power and Velocity during movements.
Let’s say we want to know how much Force, Power and Velocity a particular athlete is producing while performing a simple weight lifting exercise like the Bench Press. What do we need to do? First of all, we need to know how much is the mass the athlete will be lifting. This will be important as it is a necessary parameter for calculating Force. Secondly, we will need to know how much does the barbell travel and how long it takes to complete the full bench press motion in order to calculate the velocity of the barbell. Finally, since we know the force and velocity, we will be able to calculate the mechanical power produced.
The most common systems currently on the market use very simple technology. The Ballistic Measurement System (BMS, http://www.innervations.com/), Muscle Lab (http://www.ergotest.com/), Real Power (http://www.globusitalia.com/) and others base all the calculations on potentiometers, linear and/or rotary encoders (distance transducers) and accelerometers. Those transducers are attached to the bar (or weight stack track the displacement of the bar or weight stack (See Image) and by inputting the mass of the object tracked, the dedicated software calculates the relevant biomechanical parameters. The information can be provided in real time and stored for analysis.

All the devices used to measure force, velocity and power while performing weight lifting exercises (isotonic or isoinertial movements) are termed isoinertial dynamometers.
How can isoinertial dynamometers help us for designing a training program? In many ways. We can use isoinertial dynamometers to establish the strength and power characteristics of an athlete and compare his/her values with elite athletes and track his/her progression at different phases of the training program. Furthermore, we can use it to assign the training load and also as a biofeedback system to make sure the athlete is moving the weight as fast as he/she can. Also, due to the possibility of applying the position transducers to every moving object, we can test the athletes in open and closed chain type of exercises (i.e. Leg Press vs. Leg Extension). Furthermore, we can measure differences in Force, Velocity and then Power production between limbs.
Let’s do some examples. If we want to establish the strength and power characteristics of an athlete in the upper body, we can measure him/her while performing the bench press with 5 increasing loads (see Figure 2).

For each load we will measure Force, Velocity and Power. The information will be used to plot the Force/Velocity and Power/Velocity relationships (See Figure 3). The curves can be used to identify the lifting load needed to improve strength and power performance. In particular, if we want to identify the training load that maximises the athlete’s power output, we will chose the one that corresponds to his/her peak power. We know that in order to enhance explosive power performance, the load at which the maximal power is obtained must be used for training and the velocity of execution of the exercise used must be always maximal. This approach to strength training has been shown to produce remarkable enhancement of mechanical power (Berger, 1963; Hakkinen, 1994; Kaneko et al., 1983; Moritani et al., 1987).

Following few weeks of training, we can repeat the testing procedure and verify the effectiveness of our training programme and how the athlete is adapting. If the Force/Velocity and Power/Velocity curves are shifted to the right, we have made our athlete stronger and faster (green line, Figure 4), if the curve is the same as before, no change occurred, and if the curve moved to the left, it means the athlete is weaker and slower (red line, Figure4).

Isoinertial dynamometers can be used to detect also overtraining and overreaching, since a decrease in strength and power could be due also to an excess of training load and intensity.
The recent generation of isoinertial dynamometers provides realtime feedback during training. So, just like heart rate monitors providing information and biofeedback about the level of effort exerted by your cardiovascular system, iso-inertial dynamometers can be used to gauge your neuromuscular system during a weight training session. We can measure in real time power output (or how fast the athlete is lifting the weight) and provide feedback to the athlete to move it faster if the speed is too low. Furthermore, we could use the real time monitoring to decide how many repetitions the athlete should perform if we see any sign of fatigue and/or drop in power output. The following is an example of two different athletes performing 10 repetitions with a load equal to 70% of their 1RM. They were both asked to perform the lifts as fast as possible in the concentric phase. As you can see, Athlete A can maintain power output without significant drops for all the 10 repetitions, however Athlete B starts producing less power after the 5th repetition (Figure 5).

How can we use this information? If the goal of the session is to improve power output, then the athlete should perform a number of repetitions in which power output (and velocity of movement) is high, lifting the weight slowly in fact does not help in getting him/her faster and more powerful. Therefore, we can use isoinertial dynamometers not only for testing purposes but also to monitor single training sessions and make sure that the athlete is lifting fast and is producing high levels of power.

Are isoinertial dynamometers valid and reliable? Yes they are, provided that if you are using a linear encoder or another type of position transducer the path of the barbell, dumbbell or weight stack is linear. Few studies have been conducted comparing the parameters calculated by encoder-based systems with the same parameters measured with force plates. During Squat exercises manyh authors have found the measures to be valid and also highly reliable (i.e. Bosco et al., 1995; Rahmani et al., 2001). Also, since the best way to measure your athlete’s progression is to measure Force and Power in the exercises routinely used in training
In conclusion, if you want to measure Force, Speed, Velocity and Power in order to evaluate your athlete’s progression and to identify the proper training load, isoinertial dynamometers are your best option since they allow you to measure every lifting exercise (Barbells, Dumbbells and/or isotonic weight stack machines) with a wide range of loads.
For non linear movements (such as Olympic lifts) it is better to use accelerometers to be able to directly measure the acceleration of the barbell, dumbbell and weight stack and then calculate Force and Power.
However some principles need to be applied when measuring your athletes. If you are planning to repeat the measurements on your athletes, make sure you use the exact same range of motion used in previous measurements, use the same loads used in previous measurements and make sure the mass lifted by the athlete is exactly the same as in previous measurements to avoid that your athletes results in faster scores only because he/she is lifting a lighter barbell!

References:
Berger, R. (1963). Effect of dynamic and static training on vertical jumping. Research Quarterly, 34: 419-424

Hakkinen, K. (1994). Neuromuscular adaptation during strength training, aging, detraining and immobilization. Crit. Rev. Phys. Rehab. Med., 6: 161-198

Kaneko, M., Fuchimoto, T., Toji, H., & Suel, K. (1983). Training effect of differing loads on the force velocità relationship and mechanical power output in human muscle. Scandinavian Journal Sport Science, 5: 50-55

Moritani, T., Muro, M., Ishida, K., & Taguchi, S. (1987). Electrophysiological analyses of the effects of muscle power training. Research Journal of Physical Education, 1. 23-32

Bosco C, Belli A, Astrua M et al. (1995) A dynamometer for evaluation of dynamic muscle work European Journal of Applied Physiology 70: 379–86
Rahmani A, Viale F, Dalleau G, Lacour JR. (2001) Force/velocity and power/velocity relationships in squat exercise. European Journal of Applied Physiology 84(3):227-32

Strength testing

Strength and Power measurements for strength training planning: what is out there?

It is well accepted that success in most sports depends on the ability of the athletes to exert high levels of strength and power (Stone et al., 1994). For this reason, training programs are nowadays directed to improve those two characteristics no matter what sport the athlete is preparing for. Technology in sport has quickly developed and nowadays many tools are availble to assess an athlete’s strength and power capabilities. Moreover, recent dynamometers provide a form of biofeedback to be able to guide the athlete during his/her strength training program just like heart rate monitors provide guidance during running, rowing and cycling sessions.
Before discussing how to measure strength and power and how to use those measurements to change an athlete’s training program, we need to review some very simple biomechanical concepts.
First of all, strength relates to the ability of an individual to produce force. Force is measured in Newtons (N) and is what is required to stop, start or alter motion. According to Newton’s 2nd law, Force can be calculated as follows:
F = m x a
Where m is the mass and a the acceleration.
Acceleration can be defined as the rate of change in velocity of an object and is calculated as follows:
a = Dv/Dt
Where v is velocity and t is time. Acceleration is measured in m/s2.
When an object experiences a change in position (displacement) it has been displaced and motion has occurred. Since motion has spatial and temporal elements it is important to know the speed and/or the velocity of the object. Specifically, speed defines how fast an object is moving whereas velocity tells both how fast and in what direction the object was moving.
Velocity is calculated as follows:
v= Ds/Dt
Where s is the distance travelled by the object and t is the time needed to cover the distance. Velocity and speed are measured in m/s.
In many short duration events (i.e. sprinting, vertical jump, Olympic lifts) the rate at which muscles can produce mechanical work is often the variable limiting performance. For this reason, knowing how much power an athlete is producing in a given motion could be important to assess the effectiveness of a training program. Power production is measured as the amount of work done per unit of time.
Since mechanical work is calculated as the product of the displacement experienced by an object and the component of force acting in the direction of its displacement divided by the time needed to complete the displacement, it can be calculated in the following ways:
F x s/Dt = F x v
Power is measured in watts (W).
All of the above parameters can be calculated as an average over a range of motion or as an instantaneous value occurring at a particular instant during the displacement of an object.
Enough biomechanics! Let’s start to use it to understand how many commercial systems are using biomechanics to measure Force, Power and Velocity during movements.
Let’s say we want to know how much Force, Power and Velocity a particular athlete is producing while performing a simple weight lifting exercise like the Bench Press. What do we need to do? First of all, we need to know how much is the mass the athlete will be lifting. This will be important as it is a necessary parameter for calculating Force. Secondly, we will need to know how much does the barbell travel and how long it takes to complete the full bench press motion in order to calculate the velocity of the barbell. Finally, since we know the force and velocity, we will be able to calculate the mechanical power produced.
The most common systems currently on the market use very simple technology. The Ballistic Measurement System (BMS, http://www.innervations.com/), Muscle Lab (http://www.ergotest.com/), Real Power (http://www.globusitalia.com/) and others base all the calculations on potentiometers, linear and/or rotary encoders (distance transducers) and accelerometers. Those transducers are attached to the bar (or weight stack track the displacement of the bar or weight stack (See Image) and by inputting the mass of the object tracked, the dedicated software calculates the relevant biomechanical parameters. The information can be provided in real time and stored for analysis.

All the devices used to measure force, velocity and power while performing weight lifting exercises (isotonic or isoinertial movements) are termed isoinertial dynamometers.
How can isoinertial dynamometers help us for designing a training program? In many ways. We can use isoinertial dynamometers to establish the strength and power characteristics of an athlete and compare his/her values with elite athletes and track his/her progression at different phases of the training program. Furthermore, we can use it to assign the training load and also as a biofeedback system to make sure the athlete is moving the weight as fast as he/she can. Also, due to the possibility of applying the position transducers to every moving object, we can test the athletes in open and closed chain type of exercises (i.e. Leg Press vs. Leg Extension). Furthermore, we can measure differences in Force, Velocity and then Power production between limbs.
Let’s do some examples. If we want to establish the strength and power characteristics of an athlete in the upper body, we can measure him/her while performing the bench press with 5 increasing loads (see Figure 2).

For each load we will measure Force, Velocity and Power. The information will be used to plot the Force/Velocity and Power/Velocity relationships (See Figure 3). The curves can be used to identify the lifting load needed to improve strength and power performance. In particular, if we want to identify the training load that maximises the athlete’s power output, we will chose the one that corresponds to his/her peak power. We know that in order to enhance explosive power performance, the load at which the maximal power is obtained must be used for training and the velocity of execution of the exercise used must be always maximal. This approach to strength training has been shown to produce remarkable enhancement of mechanical power (Berger, 1963; Hakkinen, 1994; Kaneko et al., 1983; Moritani et al., 1987).

Following few weeks of training, we can repeat the testing procedure and verify the effectiveness of our training programme and how the athlete is adapting. If the Force/Velocity and Power/Velocity curves are shifted to the right, we have made our athlete stronger and faster (green line, Figure 4), if the curve is the same as before, no change occurred, and if the curve moved to the left, it means the athlete is weaker and slower (red line, Figure4).

Isoinertial dynamometers can be used to detect also overtraining and overreaching, since a decrease in strength and power could be due also to an excess of training load and intensity.
The recent generation of isoinertial dynamometers provides realtime feedback during training. So, just like heart rate monitors providing information and biofeedback about the level of effort exerted by your cardiovascular system, iso-inertial dynamometers can be used to gauge your neuromuscular system during a weight training session. We can measure in real time power output (or how fast the athlete is lifting the weight) and provide feedback to the athlete to move it faster if the speed is too low. Furthermore, we could use the real time monitoring to decide how many repetitions the athlete should perform if we see any sign of fatigue and/or drop in power output. The following is an example of two different athletes performing 10 repetitions with a load equal to 70% of their 1RM. They were both asked to perform the lifts as fast as possible in the concentric phase. As you can see, Athlete A can maintain power output without significant drops for all the 10 repetitions, however Athlete B starts producing less power after the 5th repetition (Figure 5).

How can we use this information? If the goal of the session is to improve power output, then the athlete should perform a number of repetitions in which power output (and velocity of movement) is high, lifting the weight slowly in fact does not help in getting him/her faster and more powerful. Therefore, we can use isoinertial dynamometers not only for testing purposes but also to monitor single training sessions and make sure that the athlete is lifting fast and is producing high levels of power.

Are isoinertial dynamometers valid and reliable? Yes they are, provided that if you are using a linear encoder or another type of position transducer the path of the barbell, dumbbell or weight stack is linear. Few studies have been conducted comparing the parameters calculated by encoder-based systems with the same parameters measured with force plates. During Squat exercises manyh authors have found the measures to be valid and also highly reliable (i.e. Bosco et al., 1995; Rahmani et al., 2001). Also, since the best way to measure your athlete’s progression is to measure Force and Power in the exercises routinely used in training
In conclusion, if you want to measure Force, Speed, Velocity and Power in order to evaluate your athlete’s progression and to identify the proper training load, isoinertial dynamometers are your best option since they allow you to measure every lifting exercise (Barbells, Dumbbells and/or isotonic weight stack machines) with a wide range of loads.
For non linear movements (such as Olympic lifts) it is better to use accelerometers to be able to directly measure the acceleration of the barbell, dumbbell and weight stack and then calculate Force and Power.
However some principles need to be applied when measuring your athletes. If you are planning to repeat the measurements on your athletes, make sure you use the exact same range of motion used in previous measurements, use the same loads used in previous measurements and make sure the mass lifted by the athlete is exactly the same as in previous measurements to avoid that your athletes results in faster scores only because he/she is lifting a lighter barbell!

References:
Berger, R. (1963). Effect of dynamic and static training on vertical jumping. Research Quarterly, 34: 419-424

Hakkinen, K. (1994). Neuromuscular adaptation during strength training, aging, detraining and immobilization. Crit. Rev. Phys. Rehab. Med., 6: 161-198

Kaneko, M., Fuchimoto, T., Toji, H., & Suel, K. (1983). Training effect of differing loads on the force velocità relationship and mechanical power output in human muscle. Scandinavian Journal Sport Science, 5: 50-55

Moritani, T., Muro, M., Ishida, K., & Taguchi, S. (1987). Electrophysiological analyses of the effects of muscle power training. Research Journal of Physical Education, 1. 23-32

Bosco C, Belli A, Astrua M et al. (1995) A dynamometer for evaluation of dynamic muscle work European Journal of Applied Physiology 70: 379–86
Rahmani A, Viale F, Dalleau G, Lacour JR. (2001) Force/velocity and power/velocity relationships in squat exercise. European Journal of Applied Physiology 84(3):227-32