Developing Strength & Training Rate of Force Development - Critical Review Jan 2016
By Steve, Mar 15 2019 02:26PM
Rate of Force Development (RFD) is an important component of most athletic performances in sports that require rapid force generation and most athletes would benefit from a faster RFD. By increasing an athletes power (RFD Training) results in quicker, more explosive movements for athletes, that can be anything from tennis serve or getting the bar moving sooner in lifting sports. Understanding this component of physical fitness is essential if it is to be efficiently integrated into strength and conditioning (S&C) programmes, whereby athletes first increase force output (maximum strength), and then the ability to apply this force under ever shorter timescales in movement skills specific to their sport.
Power can be described as work per unit of time, or in a manor more specific to sport, force multiplied by velocity, (Stone et al 2003) Therefore, an increase in either of these values will increase power if the other value remains constant
The most important genetic difference related to power development is the amount of muscle fibre that allows for quick muscular contraction. The body’s skeletal musculature is made up of several types of fibres. Type I fibres, the so-called slow twitch (ST) muscle fibres these are associated with less powerful more enduring function. These fibres, being more aerobic in nature, take longer to develop force and to fatigue.
Type II muscle fibres, the so called fast twitch (FT) fibres are associated with shorter bursts of explosive action. These fibres which are used during anaerobic performance develop force more quickly and fatigue more easily. Type II fibres subdivide into Type IIa and Type IIb fibres, with the a-types having greater ability for aerobic metabolism and more resistance to fatigue.
The proportion and distribution of FT fibre throughout your body depends to a great extent on the athlete’s genetic makeup. The average person has an approximate 50-50 split of FT and ST fibres throughout the body Athletes who excel at power events tend to have a higher percentage of FT fibres, and those that excel in endurance events tend to have a higher percentage of ST fibres, compared to the average person.
While an athlete cannot change the number of ST or FT firers they were born with, stimulating the FT fibres you do have, with explosive training improves their ability to fire, or contract powerfully. This is the primary reason for training RFD for increased power.
RFD, Power and the force-velocity curve
An understanding can be further enhanced by the use of the force-velocity (F-V) curve (Figure 1) from Turner, p.21 (2009) which illustrates that maximum strength is exerted under low velocities and maximum speed is produced under low loads. Thus, an inverse relationship exists between these two variables.
The placement of a sports motor skill on the F-V curve generally depends on the mass of the object to be moved, as most actions call for the movement to be executed as quickly as possible. For example, a rugby scrum requires relatively larger forces than those required to produce a Baseball pitch and are hence at opposite ends of the curve (Figure 2) from Turner, p.21 (2009)
Furthermore, most sports require a variety of motor skills (e.g., jumping, tackling and kicking) that may span a large portion of, if not the entire, F-V curve (Figure 3) from Turner, p.21 (2009)
It is beneficial to ensure that training programmes cover a large segment of the F-V curve rather than focusing on specific loads/velocities. This can be achieved through the correct exercise selection and/or training loads.
It may be useful to note that within S&C, velocity and force are often regarded as synonymous with speed and strength respectively, and hence, power is often referred to as speed-strength. Verkhoshansky (1966) describes speed-strength (SPD-STR) and strength-speed (STR-SPD), explaining these are separate training components relating to distinct areas of the curve and there are advantages to cover all areas of the curve in S&C programmes.
Training programmes incorporating jump squats, which consist of performing a countermovement jump with a barbell on the shoulders, have been shown to increase vertical jump height by between 3.5% and 13.3% (Hori et al 2008) p. 59.
Increasing power through strength Training
Maximum strength is a key factor in developing high power outputs. Power is largely dependent on the ability to exert the highest possible force (i.e., maximum strength) (Stone et al 2003) p. 739 and can be evidenced by the high and positive correlation between peak power and maximum strength in both the upper and lower body (Baker et al 2001). For example, significant correlations have been found between the 1RM squat relative to body mass and countermovement jump (CMJ) peak power, CMJ peak velocity, and CMJ height (Moss et al 1997) p198. This is further supported by (Peterson et al 2006) who found significant linear relationships between the 1RM squat, vertical jump peak power and all explosive performance tests (vertical jump, broad jump, agility t- test, sprint acceleration, sprint velocity).
Although the area of strength development is hugely important, once an athlete is considered to be strong enough for their sport, less emphasis can the then be placed on improving strength levels and more time can then be given over to RFD (alongside strength maintenance)
The UKSCA definition of Plyometrics from there 2015 “Plyometrics, Agility & speed for sports performance” course is:-
“An impact driven training task with intent to move explosively, typically incorporating a fast stretch shorten cycle” with “a contact time of around 200ms would generally be classed as plyometric.
Interestingly some older text books do not have the word “impact” in the definition, but the UKSCA believe that this is a key term that makes it plyometric. Without that term then it is considered just an explosive movement and not a plyometric movement.
Plyometrics date back to the 1960s when Russia and Eastern countries used new and unique training techniques for their Olympic athletes. Their training consisted of different styles of jumps, foot speed drills, training equipment, stretching, and resistance-training exercises that, when properly combined, increased speed. Today, the goal of plyometrics is to enhance the explosive reaction of the individual through powerful muscular contractions as a result of rapid eccentric contractions. Eccentric (lengthening) muscle contractions are followed by concentric (shortening) contractions in most skills. Energy stored during the eccentric phase is partially recovered during the concentric phase, but a potential for energy loss exists if the eccentric contraction is not immediately followed by a concentric contraction. Stretch-shortening cycle training provides an advantage for producing more power than concentric-only movements. Plyometric exercises require both eccentric and concentric movements at low- to high-intensity levels and are often referred to as “jump training” because they are a type of exercise that mixes strength with the speed of a movement to produce power.
Practical Application in Track Sprint Cyclists - Rate of Force Development
Track sprint cyclists can benefit from RFD training, as fast sprint accelerations are required to take advantage of slip streaming another rider, but then to put in a huge acceleration force to overtake the other competitor. Over 20-years ago a typical velodrome was an outdoor 400m to 333m circumference, but now most tracks are indoor and 250m. Athletes have had to increase their RFD to enable an overtaking movement to be successful on the very tight modern banked tracks.
There is very little published research into appropriate strength levels for elite track sprint cyclists to attain. General consensus suggests for an Elite sprinter it is adequate when they have the ability to back squat 1RM twice their own bodyweight to enable them to spend more time in RFD training. Obviously more strength than this could be beneficial, but not to the detriment of missing out on more RFD training. This is an issue that many good regional level sprinters have is an obsessive quest for ever bigger numbers for their 1RM back squat, as this is what they see lots of examples of on social media by their peers. RFD training does not get the same exposure on social media hence many uninformed athletes consider it is not as important.
Although traditional resistance training has been shown to improve vertical jump performance as much as 2–8 cm or 5–15%, it seems that lighter, more explosive lifts may be more effective than heavier lifts that are performed at lower velocities (Channell et al 2008) p1522. When applying this method to my own athletes I have noticed that the acceleration speed of Track Sprint cyclists have improved times and performances when a 12-week Power phase is carried out prior to a major season completion peak. This can also be backed up with (Hayes et al 2013) who states that high peak power outputs are required from Track sprint cyclists, with elite riders producing in excess of 2000W .
The following facts show that RFD is critical, when sprint riders are pedalling at a high rate, (cadence) this sets the time within which muscles must become excited, produce force while shortening, and relax before lengthening. This time frame at 130 rpm cadence (The rider has only 120deg of effective pedal stroke, therefore this is only 154ms to produce power concentrically, every half a second)
In the study (Martin et al. 2007) Understanding Sprint-Cycling Performance: The Integration of Muscle Power, Resistance, and Modelling examines the current knowledge behind the interaction of propulsive and resistive forces that determine sprint performance.
(Dorel et al. 2005) reported laboratory and competition data of world-class sprint cyclists that maximum power, normalized by frontal surface area, was significantly correlated with 200m performance velocity, suggesting that performance largely depended on the rider’s ability to overcome aerodynamic drag. Furthermore, average pedalling rates during the 200m time trial (155 ± 3 rpm) were significantly greater than pedalling rates for maximum power (130 ± 5 rpm). The authors speculated that these cyclists chose smaller gear ratios in the sprint competition to optimize power during acceleration.
This supports the case that RFD is a key component in sprint performance and gears are reduced by riders in the sprint completion to better use their available RFD. A counter argument against that is to set out to increase the riders peak and mean RFD capabilities to enable the rider to accelerate those larger gears in the sprint competition; that they have proved they can use in the 200m time trial.
Martin et al (2005) reported in an abstract that world-class sprint cyclists performed the entire 200-m time trial on the descending limb of the power– pedalling rate relationship. They reached pedalling rates (163 ± 3 rpm) that would reduce power by approximately 35% at maximum speed.
Athletes need to be reminded of the quote from the book Radcliffe & Farentinos, (2015). High-Powered Plyometrics on p. 34 is “Quality not quantity” is essential in Plyometrics /RFD training. I have successfully applied this mantra to coaching my own athletes; some athletes with very high work ethics I have found by reducing volume can in itself allow quality to increase, thereby increasing performance and the ability to achieve pb’s. Power production is very much a consequence of efficient neuromuscular processes and as such, quality should be stressed at all times. Therefore, the effectiveness of a power programme may be related to the quality of each repetition. This can also be backed up with (Retief 2004) who regularly states in his paper the huge benefits of Quality being an essential component of high RFD.
The ability of an athlete to generate power is a key goal of periodisation. This RFD can be improved through manipulation of the force-velocity curve, athletes first need to increase force output (maximum strength), and then learn how to apply this force in shorter time scales, using movement skills specific to their sport.
Injuries from plyometics can occur from unsupervised inappropriate use, or by starting plyo’s for the first time before the athlete is strong enough, or has obtained good basic movement control and skills. However further research has shown that plymetrics can significantly decrease the number of catastrophic sport injuries such as ACL tears and lower leg, foot, and ankle fractures (Hewit et all 1999)
Introducing children to resistance training but in particular RFD in the form of plymetrics is safe, effective and fun for children, Six Steps for Implementing Plyometric Training in Elementary Physical Education. Evidence indicates that, when safely implemented, plyometric training can improve muscle strength, muscle power, bone strength, speed, balance, agility, and sports performance (de Villareal et al 2010).
Methods of assessing the adaption of the athlete to RFD in various sports.
There are various methods of assessing the adaption of the athlete to RFD, it is important to select the correct testing methods appropriate to the athletes own sport. It is also important to take and record data before, during and after the set training programme period. These could be:-
• Maximum Muscular Strength (Low-Speed Strength) 1RM in Back Squat and Bench Press. This would be a good baseline measurement to evaluate if the RFD has increased alongside Strength.
• Maximum Muscular Power (High-Speed Strength) Vertical/Standing Long Jump distance monitoring, the Margaria-Kalamen stair sprint test
• Speed and Agility timed tests, i.e. T-Test, Hexagon Test, Pro Agility Test, 20m sprints (standing start/flying start)
• Velocity Based Training measuring devices i.e. Push, Beast, is a good way to monitor improvements in speed (m/s) of movement against bar weight used, this can be used to evaluate Power output.
• 1RM of actual weight used in the power exercises i.e. Olympic lifts, Cleans etc.
• Sport specific testing of RFD in the athletes own sporting environment.
• Jump mats could be used and are accurate in the CMJ and SJ’s. However Kenny et al (2012) demonstrated that the fast SSC and reduced contact times associated with DJ’s resulted in errors but CMJ and SJ’s are accurate.
There are many ways of RFD training, Plyometrics, Ballistic, Power, Explosive movements; all these methods can be used, when delivered with maximum intent. Gradual technical development in all of the above, taking the time to develop the skills and physical qualities will enable athletes to increase the overall effectiveness of a training programme and minimise the injury risk.
The athlete should initial ensure adequate work capacity has been obtained from Strength and Stabilization developed in the general prep phase of the programme. Then by moving on to a strength development phase. From this stage the athlete should see positive adaptations in neuromuscular programming and an increase in type IIa fibres. These adaptations can then be exploited to further enhance power and velocity through RFD training.
Furthermore, because strength is seen as the prerequisite of power, then adequate amounts of strength maintenance still need to be incorporated throughout the entire cycle.
The F-V is a good illustration of the types of RFD training required for a good S&C programme, it would be best to cover a larger range of loads to accommodate the ever changing resistance and velocities experienced during competition.
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