Pedro E. Alcaraz is a European Ph.D. in Sport Sciences. He was appointed Master in High Performance Sport by the Spanish Olympic Committee, is a Professor of Methodology and Periodization of Training, Faculty of Sports, and is head of UCAM Research Center for High Performance Sports. Dr. Alcaraz serves as Director of the Biomechanics Lab, Universidad Católica San Antonio de Murcia, Spain (2010 – Present); Head of OP_EN_RED Research Group, Section of Sport Sciences; Deputy Head of Masters in High Performance Sport: Strength & Conditioning (Spanish & English version), and Master in Strength & Conditioning and Rehabilitation in Soccer; and Director of UCAM Spanish Sports University, Universidad Católica de Murcia, UCAM.
Freelap USA: The change of direction deficit is growing in popularity for the evaluation of player abilities. Can you share why it’s important to communicate the value of this measurement to team coaches who may not understand the eccentric capacities of players? Often, the team coach assumes change of direction is about technique only.
Dr. Pedro E. Alcaraz: Regarding the change of direction deficit (CODdeficit), I think there are many things to say, because it has been proposed as an adequate method for assessing COD ability in different team sports, such as netball, soccer, handball, and youth cricket and basketball. The CODdeficit reports the additional time required to perform a directional change when compared to the time needed to cover the same distance in a linear sprint or, alternatively, the difference in velocity between the linear sprint and a COD task of equal distance. In summary, this novel variable is an indicator of the athlete’s efficiency in changing direction, based on their maximum linear velocity, which provides a more precise measurement of COD ability as a separate quality. Curiously, some studies performed with elite soccer and handball players reported that faster and more powerful athletes tend to be less efficient when changing direction (i.e., presenting greater CODdeficits).
The COD deficit indicates an athlete’s efficiency in changing direction, based on their maximum linear velocity, which gives a more precise measure of COD ability as a separate quality. Share on XAnyway, I think we do not clearly know the information that the CODdeficit really provides to us. First, note that you can use this variable to compare athletes with themselves, but not so much to other players. This is because we have observed that an athlete who is faster in a straight line will likely create a greater deficit (having a higher linear velocity, they must decelerate more). If the athlete’s body mass (BM) is a factor, the weight difference will affect the final result. Therefore, the relative strength of the athlete will be a key component and, specifically, eccentric abilities and performance. Of course, the technique in the change of direction is fundamental, but perhaps not the most decisive factor.
All of this is explained by mechanical factors related to the principle of inertia. Therefore, our research group, together with Irineu Loturco’s group (one of the world leaders on this topic), thinks that in the future, when this variable is used to measure performance and is able to compare both intra- and inter-players, the “sprint momentum” must be taken into account to correct factors related to the linear velocity and BM of the subject.
On the other hand, with respect to eccentric strength, consider that when a player has a high running speed and decides to make a COD, all their kinetic energy must be absorbed to make this change. This occurs thanks to a high capacity to generate and store elastic energy, where the eccentric muscle activation by the athlete is decisive. In fact, in a recent study we have done with soccer players (currently under review), we found that training with a weighted vest—which produces a greater “sprint momentum,” and therefore a higher kinetic energy—generates a decrease in the CODdeficit when compared to the same training, with the same load, but with a horizontal electromechanical resistance, which does not generate this increase in the “sprint momentum.” In addition, there were quite a few players in the weighted vest (WV) group who managed to increase their sprint maximal velocity (Vmax) after eight weeks of training.
This is a very striking aspect, knowing the Vmax to CODdeficit ratio explained above. That is, a priori, by increasing your sprint Vmax after the intervention, it could also produce an increase in the CODdeficit. However, in our study, the group that trained with weighted vests obtained a significant reduction with a large effect size in the CODdeficit, despite significantly increasing their maximum sprint speed. Therefore, the weighted vest must be considered a highly specific method for training the ability to change direction and agility.
In summary, the CODdeficit is very useful to measure performance in team sports, but very dependent on factors that cannot be modified. In this sense, the test must be adjusted with the “sprint momentum” of each subject. On the other hand, optimal work with the technique of COD with athletes requires eccentric training that activates the stretch shortening cycle (SSC) in specific positions. In addition to its low cost, this resisted training with a weighted vest is a very useful, since it works both eccentric strength and the SSC.
Freelap USA: Circuit training may be effective or not effective based on baseline fitness levels. Could you share how fitness coaches for teams can use your research to design better workouts when working with athletes in the early part of training?
Dr. Pedro E. Alcaraz: As you know, improvements in sports performance in most team sports are determined by a high demand of aerobic/anaerobic metabolism, maximal strength, mechanical power, speed, and agility. Thus, success or failure in these sports is largely dependent on the optimal training plan used to develop these abilities, which are often trained simultaneously (i.e., concurrent training).
Resistance circuit-based training (RCT) is an effective training method for the concurrent development of maximum oxygen consumption (VO2max) and one repetition maximum (1RM) in healthy adults, independent of participant and load characteristics. However, a proper manipulation of the variables that determine the training load could intensify VO2max or 1RM adaptations. In addition, sex and fitness level were observed to have an overall higher effect on 1RM bench press. This means that RCT could be more beneficial for women and sedentary participants in the development of maximal strength, while men and trained participants probably need a higher training intensity to increase the 1RM.
Currently, RCT has become very popular for strength training in team sports, especially in the preseason. The main problem you’ll observe when you analyze the circuit training of the teams in preseason is that the neuromuscular load of the players is controlled little or not at all, and the intensity is, in many occasions, low. This fact makes it difficult sometimes to improve the maximum strength of our players and limits the improvement of power and athletic performance.
Resistance circuit-based training, if properly designed, is an incredible tool to improve aerobic & anaerobic metabolism, max strength & power, and specific qualities. Share on XStudies carried out by our research group have shown that this type of training has a high energy expenditure when compared to traditional training, and a high aerobic and anaerobic demand. All this without losing execution velocity in each repetition and volume of training, despite the fact that work time is reduced by 66%. Additionally, I would like to emphasize that RCT, if properly designed, is an incredible tool to improve aerobic and anaerobic metabolism, maximum strength and power, and specific qualities. For example, the fatigue index after a repeated sprint ability test, with only 30 minutes of training.
My recommendations for team sports are the following:
- Use high loads (~6RM), as long as you want to improve from a neuromuscular point of view and your maximal strength, especially in preseason. Use more power-oriented loads (lower loads, at the maximum possible velocity) in season, to maintain the neuromuscular development reached in the preseason.
- Combine muscle groups from different parts of the body in short circuits of 3-4 exercises, in order to provide a recovery of 3-5 minutes for the same muscle group. The studies we are developing have shown that the fatigue that occurs with this type of training is mainly peripheral, when compared to traditional strength training. Therefore, allowing adequate recovery, the quality (measured by the technique and velocity of execution) of each series will not be altered.
- In preseason, try to repeat the same muscle group twice a week. In season, try to at least work all the determining muscle groups once a week. (This recommendation will depend a lot on the discipline. For example, sprinters should keep to two times per week in season, but control the total load in the peaking.)
- Modify your circuit training plan approximately every eight weeks to avoid a plateau and to be able to continue working other areas of the force-velocity curve.
- Remember that high-intensity resistance circuit-based (HRC) training produces high levels of fatigue, so be careful what you do afterward. My recommendation is that after this type of training, you apply an aerobic task or train the technical tactics in fatigued conditions. Either way, I want to emphasize that HRC training in team sports, when applied well, can reduce your body fat without excessively increasing your muscle mass. You can also improve your anaerobic threshold, and, in some cases, it may also improve your oxygen consumption. But above all, it reduces the fatigue index when performing repeated sprint ability tasks, improving maximum strength and power.
Freelap USA: Resisted sled sprints are often loaded heavy to promote horizontal force. Yet many users still go lighter to encourage sprinting with faster ground contact times that foster SSC of the ankle complex. Could you explain some of the possible negative consequences of going too heavy with athletes who are looking to get faster?
Dr. Pedro E. Alcaraz: I think we have reached the hot topic of the interview… ha ha ha. First of all, I want to clarify that I have nothing against resisted sled training (RST) with very high loads, as long as heavy sleds are used to improve the horizontal force of the athlete, which is key in the first steps when starting from a stationary position in sprinting (i.e., sprinters). Recently, a group of researchers who are very active on social media confused people, making it seem that if you do not use RST with very high loads, you cannot improve sprint performance.
I disagree with these researchers. This was clearly seen in the meta-analysis we recently published. It was also confirmed with another work recently published by Pareja-Blanco et al. (2019), which specifically compares the effect of eight weeks of RST with high loads (80% BM) against low loads (12.5% BM) in different situations. This study shows that it is much more effective to train with a combination of half-squats, with overloads of 40-55% 1RM and RST at 12.5% BM, than with the same training but with RST at 80% BM. In fact, this last option did not improve the performance in any sprint section analyzed (0-30 meters, 10-20 meters, 10-30 meters).
I also disagree on another point put out by this group, that maximum power production with resisted sleds is ideal with very high loads. However, I want to clarify the following: Producing high levels of power does not ensure you improve sprint performance, as this recent study has shown. (In any case, it ensures you improve power.)
It is curious to see how many coaches are obsessed with improving power, when what players need to improve is performance, says @PedroE_Alcaraz. Share on XIt is curious to see how many coaches are obsessed with improving power, when what needs to be improved in players is performance. In this case, that is the sprint, the change of direction ability, the agility, and/or the jump. Therefore, the end goal should be running faster, changing direction faster, and jumping higher, regardless of the mechanism that causes this improvement (which will sometimes be power, but can also be other multiple factors). I firmly believe that the best way to improve sprinting is by running fast, as Pep Guardiola, head coach of Manchester City FC, says: “The best way to learn to play soccer is by training with a ball when you are a kid.” Similarly, if we want to be fast, we have to sprint, and then improve the athlete with other training means and methods, depending on their needs.
I always use the same example: Coaches are the ones who know the most about training and researchers should look more at what they do or have done previously. Of course, we, as researchers, should explain the mechanisms by which these methods increase performance.
In this sense, why is RST with very high loads almost never used by coaches, if it is so good? I think the answer is easy: If we want to train the neuromuscular system of an athlete, the adaptations will be totally specific to what they do from a technical point of view (here, this includes movement pattern, gesture velocity, muscle groups involved, strength qualities manifestation, etc.), when using RST with very high loads. We only respect the movement pattern (and only in athletes with a very developed sprint technique), but we completely ignore the rest of the factors. Therefore, can RST be used?
Yes, to improve the horizontal force, which is decisive in the first steps of a sprinter. But what about the remaining 40 strides, in which the contact time is minimal, and the stiffness, the stretch reflex, and the SSC are fundamental? Above all, where we have to significantly withstand the action of gravity to raise our center of mass (COM) a few centimeters from the ground, during much of the race, and avoid a high oscillation of the COM?
My experience, currently as a researcher and, in my first years after finishing a degree in sports sciences, as a coach, is that when you use RST with excessive load, the running technique is modified in excess and makes you sprint in a sitting position, which is totally contrary to the ideal run technique. In addition, research associates this position with the frequent position of injury of the long head of the biceps femoris. Curiously, this is one of the muscle groups that has greater incidence and involvement in team sports such as football, despite all the work that is being done to avoid the problem. On the other hand, RST with very high loads, for athletes who do not have a proper movement pattern, can make them modify their run pattern negatively, with the consequence of being much less effective and impairing the application of forces.
For me, the most detrimental thing is that the leg stiffness with excessively high loads is disrupted. This is one of the most decisive mechanical variables for sprinters in the phase of maximum speed or when they perform fly-sprints. Therefore, we must be very careful that when our athletes try to imitate the gesture of the sprint, the optimal mechanics are as close as possible to that of a sprint without overload.
Finally, I want to comment that this “dogma” of resisted sled training with high loads, which some researchers want to sell us to make athletes run faster, is “selling” a lot in the world of soccer. It is curious that people want to introduce this very harmful training, which, above all, is oriented to improve horizontal force in a sport where most high-intensity actions occur in a more upright position, even with COD. Therefore, methods and means more oriented toward improving vertical force and eccentric strength (e.g., weighted vests), would make much more sense in these sports.
Freelap USA: Hypoxic training is now more accessible than ever. Can you outline a few important considerations for sports teams looking to take advantage of this methodology?
Dr. Pedro E. Alcaraz: In recent years, the alteration of the intra-muscular environment via hypoxia has received research and practical interest as another method to enhance the physiological experience of resistance training (RT). This was originally investigated by restricting blood flow to the exercising muscles to elicit localized hypoxia, which has been repeatedly shown to increase muscle size and strength even when lifting very light loads. However, considering that this strategy can only be applied to limb muscles, researchers have also begun to examine whether performing resistance exercises in systemic hypoxia (via breathing hypoxic air) can provide similar benefits for whole-body training sessions. Considering that one of the fundamental responses to exercise in hypoxia is an increased reliance on anaerobic metabolism, the benefits of resistance training in hypoxia (RTH) are thought to be mediated largely by increases in metabolic stress.
Resistance training in hypoxia can be very useful for athletes with an immobilization injury, in order to quickly recover muscle mass, says @PedroE_Alcarz. Share on XIn our investigations, we have seen that an excessive hypoxia (> 3000 meters) can do a lot of damage to the neuromuscular system, but that a moderate hypoxia (~1800 meters) can be beneficial, especially for an improvement of the muscle size. I think this type of training can be very useful for athletes who have had an immobilization injury, in order to quickly recover muscle mass. It can also be useful if you want to improve metabolically, keeping in mind that the neuromuscular system may be affected. Therefore, while we observed no significant benefits for RTH compared with normoxia RT in muscle size, small effects were evident in favor of larger increases in muscle cross-sectional area and strength following RT in normoxia. These findings suggest that some individuals may benefit more from RTH compared with normoxia, which would be important in well-trained athletic cohorts where small changes in physical attributes are difficult to achieve, and may therefore be meaningful.
Freelap USA: Weighted vest sprinting is growing in popularity, yet the guidelines are often borrowed from sled training. As power seemed to favor lighter loads, could you share some simple recommendations for weighted sprints?
Dr. Pedro E. Alcaraz: I’m glad to see that you ask me about training with weighted vests because, as I said throughout the interview, I think it’s a very versatile way to train. However, as you say, it has always been in the shadow of resisted sled training, even knowing that both types of training involve different stimuli.
First of all, I would like to emphasize that this type of training became very popular thanks to Carmelo Bosco’s studies in the ’80s. However, I think the approach he shared at that time made many coaches use WV training with a different orientation from the training today. Secondly, I would also like to add that this type of training is very versatile, because it allows you to work the force in both the vertical and horizontal axes; that is, it can be very useful to improve both the vertical and horizontal jumps, including sprinting and COD. The interesting thing about weighted vests is that athletes wearing them close to their COM does not limit any specific gesture, but allows for increasing the inertia of the segments under concentric and eccentric activations, incorporating the SSC.
With respect to the recommendations, the studies that we have carried out in our research group show that peak power production when performing a sprint with a weighted vest is reached with low loads. This does not mean that we should always use the optimal peak power load, so there is no excuse for using this method with very high overload.
Second, this method was thought to be good as long as it was used in a bounding fashion. In fact, it has been and continues to be widely used in training, although it has been poorly researched, especially regarding the effects and adaptations of its chronic application over several weeks. The few studies that have been published only investigated the acute effects of the modality, but a recent study that we have under review shows that WVs are also effective when used in sprinting, as compared to sprints with horizontal electromechanical loads for improving sprint performance. Due to the high eccentric load that the body generates when increasing inertia, note the aforementioned recommendations when applying this style of training.
In this study, the load used was never higher than 20% BM. Based on the previous equations that we calculated, the loads used, as far as a WV is concerned, corresponded to velocity losses of 5-10% of the maximum velocity under unloaded conditions. Specifically, we made combinations of different loads throughout the eight weeks of training the players, starting with 10%, progressing to 20%, and finishing the last weeks with loads of 10% BM. One of the reasons that we didn’t use loads greater than 20% BM was that, in a previous study of acute effects, we saw that with loads greater than 20% BM, the effectiveness of application of force of the athlete was significantly compromised on the ground, as evaluated with the maximal rate of force (RFmax) and the rate of decrease in the ratio of force (DRF).
My recommendations for training with weighted vests, apart from not using loads over 20% BM, are that when you want to develop the sprint, COD, or jump:
- Use it at least twice a week.
- There should be a separation of at least 48 hours between each session.
- Hold the session when you are fresh, and at the beginning of the session, after adequate warm-up.
- Don’t exceed a daily volume of 200 meters, and keep the volume of the mesocycle at approximately 2,400 meters.
- Run the program at least six weeks.
- Remember that recovery in these cases is fundamental, so provide one minute for every 10 meters sprinted. If this training is for sprinters, you can do both days with linear sprints. If this is for team sports, I would combine a day with linear sprints and another day with COD. As we have seen in the research under review, resisted training that combines linear displacements and COD can be highly effective in team sports such as soccer.
As a general summary of this interview, I would like to specify that I have no interest in selling anything, much less a type of training, since the training must be multifactorial and multifaceted. My passion for science is marked by my love for training on the one hand, and by performance on the other. I believe in the individualization of training and the principles of specificity, reversibility, overload, periodization, etc.
I believe that the success of a performance lies in using all the tools we have, knowing the final objective of each medium and method, says @PedroE_Alcaraz. Share on XFurthermore, I believe that the success of a performance lies in using all the tools we have, knowing the final objective of each medium and method. What we do with those means and methods for the overall performance of the athlete matters most. At the end of the match or season, the athlete who wins, is the fastest, or scores the most goals or shots is what we want, and not the one that necessarily generates more mechanical power or lifts more pounds in half squats.
Acknowledgments
I would like to thank my entire research team for their work. Without them, it would not have been possible to carry out research of this magnitude. I especially want to mention the work of those who led some of the studies I used for this interview—in particular, Cristian Marín-Pagán, Tomás T. Freitas, Jorge Carlos-Vivas, and Domingo J. Ramos-Campo.
Some Related References
Alcaraz PE, Palao JM, Elvira JL, Linthorne NP. “Effects of three types of resisted sprint training devices on the kinematics of sprinting at maximum velocity.” J Strength Cond Res.2008 May;22(3):890-97.
Alcaraz PE, Sánchez-Lorente J, Blazevich AJ. “Physical performance and cardiovascular responses to an acute bout of heavy resistance circuit training versus traditional strength training.” J Strength Cond Res. 2008 May;22:667-71.
Alcaraz PE, Palao JM, Elvira JL. “Determining the optimal load for resisted sprint training with sled towing.” J Strength Cond Res. 2009 Mar;23(2):480-85.
Alcaraz PE, Perez-Gomez J, Chavarrias M, Blazevich AJ. “Similarity in adaptations to high-resistance circuit vs. traditional strength training in resistance-trained men.” J Strength Cond Res. 2011 Sep;25(9):2519-27.
Alcaraz PE, Romero-Arenas S, Vila H, Ferragut C. “Power-load curve in trained sprinters.” J Strength Cond Res. 2011 Nov;25(11):3045-50.
Alcaraz PE, Elvira JL, Palao JM. “Kinematic, strength, and stiffness adaptations after a short-term sled towing training in athletes.”Scand J Med Sci Sports. 2014 Apr;24(2):279-90.
Alcaraz PE, Carlos-Vivas J, Oponjuru BO, Martínez-Rodríguez A. “The Effectiveness of Resisted Sled Training (RST) for Sprint Performance: A Systematic Review and Meta-analysis.” Sports Med. 2018 Sep;48(9):2143-65.
Carlos-Vivas J, Freitas TT, Cuesta M, Perez-Gomez J, De Hoyo M, Alcaraz PE. “New Tool to Control and Monitor Weighted Vest Training Load for Sprinting and Jumping in Soccer.” J Strength Cond Res. 2018 Apr 26.
Carlos-Vivas J, Marín-Cascales E, Freitas TT, Perez-Gomez J, Alcaraz PE. “Force-Velocity-Power Profiling During Weighted Vest Sprinting in Soccer.” Int J Sports Physiol Perform. 2018 Nov 14:1-28.
Freitas TT, Alcaraz PE, Bishop C, Calleja-González J, Arruda AFS, Guerriero A, Reis VP, Pereira LA, Loturco I. “Change of Direction Deficit in National Team Rugby Union Players: Is There an Influence of Playing Position?” Sports (Basel). 2018 Dec 21;7(1).
Freitas TT, Calleja-González J, Carlos-Vivas J, Marín-Cascales E, Alcaraz PE.
“Short-term optimal load training vs a modified complex training in semi-professional basketball players.” J Sports Sci. 2018 Aug 1:1-9.
Loturco I, Pereira LA, Freitas TT, Alcaraz PE, Bishop C, Zaneti V, Jeffreys I. “Maximum acceleration performance of professional soccer players in linear sprints: is there a direct connection with change-of-direction ability?” Plos One. 2019 April.
Martínez-Valencia MA, González-Ravé JM, Santos-García DJ, Alcaraz PE, Navarro-Valdivielso F. “Interrelationships between different loads in resisted sprints, half-squat 1 RM and kinematic variables in trained athletes.” Eur J Sport Sci. 2014;14 Suppl 1:S18-24.
Martínez-Valencia MA, Romero-Arenas S, Elvira JL, González-Ravé JM, Navarro-Valdivielso F, Alcaraz PE. “Effects of Sled Towing on Peak Force, the Rate of Force Development and Sprint Performance During the Acceleration Phase.” J Hum Kinet. 2015 Jul 10;46:139-48.
Muñoz-Martínez FA, Rubio-Arias JÁ, Ramos-Campo DJ, Alcaraz PE. “Effectiveness of Resistance Circuit-Based Training for Maximum Oxygen Uptake and Upper-Body One-Repetition Maximum Improvements: A Systematic Review and Meta-Analysis.” Sports Med. 2017 Dec;47(12):2553-68.
Pareja-Blanco F, Asián-Clemente JA, Sáez de Villarreal E. “Combined Squat and Light-Load Resisted Sprint Training for Improving Athletic Performance.” J Strength Cond Res. 2019 Apr 23.
Ramos-Campo DJ, Rubio-Arias JA, Dufour S, Chung L, Ávila-Gandía V, Alcaraz PE. “Biochemical responses and physical performance during high-intensity resistance circuit training in hypoxia and normoxia.” Eur J Appl Physiol. 2017 Apr;117(4):809-18.
Ramos-Campo DJ, Martínez-Guardado I, Olcina G, Marín-Pagán C, Martínez-Noguera FJ, Carlos-Vivas J, Alcaraz PE, Rubio JÁ. “Effect of high-intensity resistance circuit-based training in hypoxia on aerobic performance and repeat sprint ability.” Scand J Med Sci Sports. 2018 Oct;28(10):2135-43.
Ramos-Campo DJ, Scott BR, Alcaraz PE, Rubio-Arias JA. “The efficacy of resistance training in hypoxia to enhance strength and muscle growth: A systematic review and meta-analysis.” Eur J Sport Sci. 2018 Feb;18(1):92-103.
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