Effects of various training interventions on rate of force development
Introduction: Athletic success often depends on an individual’s ability to exhibit explosive strength. Explosive strength is the ability to rapidly generate force, often from a state of complete muscle relaxation. One way to analyze an athlete’s explosive strength is to measure their rate of force development (RFD). RFD is derived by plotting force and time on a graph (force-time curve) during an explosive contraction or movement. There are multiple advantages in measuring an athlete’s RFD. First, in comparison to maximal voluntary contraction (MVC), RFD appears to have a greater relationship to sport-specific performance. Second, RFD has greater sensitivity to acute and chronic neuromuscular adaptations (Maffiuletti, Aagaard, Blazevich, Folland, Tillin, & Duchateau, 2016). Third, RFD may be influenced by multiple physiological mechanisms including maximal strength, type of contraction, fiber type, and neural determinants (Maffiuletti, Aagaard, Blazevich, Folland, Tillin, & Duchateau, 2016).
Physiologically, there are many factors which influence an athlete’s ability to generate force rapidly. Neural determinants of RFD include motor unit recruitment, discharge rate, and muscle activation. Recruitment during rapid contractions is consistent with the size principle. Meaning smaller and lower threshold units are recruited prior to larger and higher threshold units. However, unlike slow contractions where increasingly larger units are recruited gradually, rapid contractions demonstrate recruitment of larger units at much lower forces. RFD is also influenced by discharge rate, especially during the early stages of muscle contraction. Discharge rate can be defined as the frequency in which nerve impulses are generated. Smaller time between impulse spikes indicates greater discharge rates. Greater discharge rates are associated with higher levels of RFD. For example, older adults demonstrate slower RFD (48%) and discharge rate (27%) than younger adults (Maffiuletti, Aagaard, Blazevich, Folland, Tillin, & Duchateau, 2016). Two spikes which occur less than 5 ms apart is called a doublet. Doublets often occur during the initial phase of a contraction and their presence can be influenced by training. Twelve weeks of dynamic dorsiflexion with light loads increased the percentage of doublets from 5.2% to 32.7% (Maffiuletti, Aagaard, Blazevich, Folland, Tillin, & Duchateau, 2016). Overall, doublets are a mechanism which enhance contraction velocity with greater influences during the early phase. The final neural determinant of RFD is muscle activation. Muscle activation appears to play a key role in RFD. Surface EMG studies have demonstrated voluntary activation during early time periods is less than electrically induced contractions. Additionally, a positive association (r2=0.76) was found when voluntary force was expressed relatively to the force produced by the electrical stimulation at the same time frame with surface EMG of the quadriceps (Maffiuletti, Aagaard, Blazevich, Folland, Tillin, & Duchateau, 2016). The results of these electrical stimulation studies indicates muscle activation has a greater influence on RFD than muscle properties during the early stages of contraction.
Although neural determinants play a significant role in RFD, they fail to completely explain differences in muscle activation rates. Muscle size, fiber type, and architecture also appear to play a role in RFD. Type II fibers have shown the ability to produce tension faster than type I fibers. Type II fibers have greater calcium release per action potential in addition to fast myosin, troponin, and tropomyosin isoforms. These factors lead to greater cross-bridge cycling rates. Muscle size and architecture have also been shown to significantly correlate with voluntary RFD. How long the muscle has to contract plays a role in muscle size and architecture on RFD: the longer the muscle has to contract, the more size and architecture play key roles. Strength explains 78% of the variance in RFD over the first 200 ms (Maffiuletti, Aagaard, Blazevich, Folland, Tillin, & Duchateau, 2016).
Due to its close relationship with athletic success, it is imperative exercise experts understand the best methods to develop RFD. Therefore, the purpose of this review was to elucidate the effects of various training interventions on RFD.
Purpose: The purpose of this review of the literature is to examine the influences of various training interventions on RFD.
Definitions:
RFD- rate of force development
RFDr- rate of force development normalized to maximal voluntary contraction
RFDmax- peak rate of force development
FRC-peak force minus bodyweight
RTD: rate of torque development, the same as rate of force development except expressed in newton meters.
RTDpeak: measure of the steepest slope of the torque/time curve
Influences of resistance training methods on rate of force development
F.B.Oliveira, Rizatto, and Denadai (2013) studied the effects of fast-velocity concentric isokinetic resistance training on rate of force development. The subjects were eighteen healthy men whom had not participated in resistance training in the past six months. They were randomly divided into a fast-velocity group and control group (no training). The researchers were not blinded to the intervention and the study was a pre/posttest design. The intervention consisted of 6 weeks of unilateral fast-velocity concentric isokinetic knee extensor resistance training. The training program was performed 3 times per week for a total of 18 sessions. The training was periodized with the subjects beginning with 3 sets of 12 repetitions and working up to 6 sets of 10 repetitions. Each repetition was to be performed as fast and forcefully as possible. The final week was a taper and training volume was reduced to 3 sets of 12 repetitions to allow for recovery. The rest periods were 2 minutes between each set. The isokinetic knee extension device was set to 180°/sec and the subjects were instructed to perform each contraction as fast and forcefully as possible. Maximal strength and the force-time curve were generated by having the subjects push into stationary dynamometer at a knee angle of 75 degrees. There were no significant results for maximal muscle strength in either group. There were significant findings in the training group for both RFDmax (17,872 ±6254 to 28,991 ± 12472 N∙m∙s -1, P = 0.0005) and RFDrmax (5756 ± 1389 to 8380 ±2596% MVC∙s -1, P = 0.001). Significant results for the training group were also noted for RFD at time intervals from 0-90ms (39.2 ± 22.2–71.3 ± 45.6%, P<.05) and for RFDr from 0-70ms (33.5 ±25.5–56.2 ± 43.3%, P<.05). No significant results were found after the 90ms time interval. In conclusion, fast-velocity concentric isokinetic resistance training elicits greater RFD training adaptations verses a control group. These improvements tend to occur at earlier rather than later time periods.
F. Oliveira, A. Oliveira, Rizatto, and Benedai (2013) explored the effects of explosive isometrics on rate of force development. The subjects were 18 healthy males whom had refrained from participating in resistance training for the previous 6 months. The subjects were randomly assigned to either an explosive isometric group or a control group (no training). The researchers were not blind to the intervention and the study was a pre/posttest design. The intervention consisted of 6 weeks of unilateral explosive isometric knee extensor resistance training. The training program consisted of three sessions per week for a total of 18 sessions. Isometric exercise was performed at a knee angle of 75 degrees and subjects were instructed to perform isometric efforts as fast and forcefully as possible. The goal during each repetition was to achieve at least 90% of maximal voluntary contraction as quickly as possible. The repetition was held for 5 seconds (s). The training was periodized with the subjects beginning with 3 sets of 6 repetitions each held for 5s and ending with 3 sets of 10 repetitions each held for 5 seconds. The rest period was 2 minutes between each set. The final week provided a taper for recovery and training volume was dropped to 3 sets of 8 repetitions held for 5s each. There was a significant main effect of training for MVC (F = 7.43, p = 0.01) and a 19% increase in MVC (no changes for control). There was no significant main effect of training for RFDmax (F = 3.30, p = 0.10) and RFDr (F = 0.17, p = 0.68). Significant findings in the training group were found for RFD (F = 48.32, p < 0.001). However, there were no significant findings when RFD was normalized for MVC: RFDr (F = 0.49, p = 0.48). Post-hoc test showed significant increase of RFD at 0-10 ms (28%, p = 0.006) and at 0-20 ms (22%, p = 0.03) for the training group only. In conclusion, it appears explosive isometrics create different training adaptations compared to fast-velocity concentric training. Explosive isometrics improved maximal muscle strength to a greater degree but failed to increase RFDmax and RFDr. RFD did significantly increase, but not when normalized for maximal voluntary contraction.
A similar group of authors, A. Oliveira, Corvino, Caputo, Aagaard and Denadai (2015), examined the effects of fast-velocity eccentric training on early and late RFD. The subjects were 20 healthy males whom were recreationally active. The subjects were randomly assigned to a fast-velocity eccentric group or a control group (no training). The researchers were not blinded to the intervention and the study duration was 11 weeks (8 weeks of training, 1 week familiarization, 2 weeks for testing). The intervention consisted of 8 weeks of unilateral fast-velocity isokinetic eccentric training. The training program was performed 3 times a week for a total of 24 sessions. The isokinetic device was set at 180°/sec, and the contractions were performed from 10-90 degrees of knee flexion. The training program was periodized with the subjects beginning with two sets of 8 maximal repetitions during weeks 1 and 2 and progressing up to 6 sets of 8 repetitions. Weeks 7 and 8 were a taper where training volume was reduced to 3 sets of 8 repetitions to allow recovery. Rest between sets was one minute. Maximal strength and the force-time curve were generated by having the subjects push into stationary dynamometer at a knee angle of 75 degrees. Maximal voluntary contraction improved 28% in the training group with no changes in the control group (p<0.01). RFDpeak increased significantly by 48% in the training group with no changes in the control (p<0.01). No changes in RFDtime were found. RFDinc and RFDrel increased during the first two time intervals for training group only, 0-50 ms and 50-100 ms, 30-32% (p<0.05). In conclusion, it appears fast-velocity eccentric training can improve both maximal voluntary contraction and rate of force development. The results appear similar to the concentric fast-velocity training, where the early time periods of RFD responded better than late (0-100ms). It appears the type of contraction plays a significant role in training adaptation to explosive oriented resistance training. Fast concentric training improves early, RFDrel, and RFDmax but has little effect on maximal strength. Fast eccentric training enhances early RFD and maximal voluntary contraction. Explosive isometric training improves maximal strength but fails to improve RFD when normalized for MVC.
Mangine, Hoffman, Wang, Gonzalez, Townsend, Wells, Jajtner , Beyer, Boone, Miramonti, LaMonica, Fukuda, Ratamess & Stout (2016), compared high intensity low volume resistance training to high volume moderate intensity and their effects on force production, RFD, and barbell velocity. The subjects were 33 physically active, resistance trained men, whom had at least 2 years of training experience. They were randomly assigned to either a high intensity, low volume group (INT) or a high volume, moderate intensity group (VOL). The researchers were not blinded to the training program. The study was a pre/posttest design and carried out for 8 weeks. Barbell velocity was measured during the bench press and back squat using a linear transducer (tendo unit). The barbell velocity was measured during a single repetition maximum (1-RM) in each exercise. RFD was generated during an isometric mid-thigh pull on a force plate. The bar was placed mid-thigh which corresponds to the second pull of an Olympic lift. The training program was carried out 4 times a week for 32 total sessions. Each session consisted of the same exercise sequence performed for 4 sets. The INT group exercises at 90% 1-RM for 3-5 repetitions with 3 minutes of rest between sets. The VOL group exercised at 70% 1-RM for 10-12 repetitions with 1 minute rest between sets. Volume-load was ~ 130% greater in the VOL group. There were significant improvements (p < 0.001) in BP and SQ barbell velocity for both groups with no differences occurring between groups in either BP (F = 0.012, p = 0.915, η2 = 0.12) or SQ (F = 0.99, p = 0.329, η2 = 0.24). Significant differences between groups was found for INT for peak FRC, FRC output at 30-200ms, and RFD at 50-90 ms (p<0.05). Significant improvements in peak FRC and FRC output at 30–200 ms were observed for INT but not for VOL (p < 0.05). For RFD, a significant improvements were found for INT at 50 ms (p = 0.040) only, and a trend was observed at 90 ms (p = 0.052). VOL failed to produce any significant findings for RFD. In conclusion, high intensity, low-volume resistance training produces greater effects on RFD than high volume, moderate intensity resistance training.
Thompson, Stock, Shields, Luera, Munayer, Mota, Carrillo, & Olinghouse (2015), investigated 10 weeks of deadlift training on rate of force development and vertical jumping capabilities. The study consisted of 54 college-aged men and women whom were not currently participating in physical exercise. The subjects were randomly split into a control (n=20, mean age 22.9 years) and a training group (n=34, mean age 22.8 years). The investigators were not blinded to the intervention. Prior to baseline testing, a familiarization procedure was performed to allow practice of the testing procedures. The study was conducted for a total of 10 weeks. Pretest baseline measurements included isometric strength testing, rate of torque development (RTD), and countermovement vertical jump testing. Isometric strength testing was calculated using a biodex isokinetic dynamometer in the seated position. Subjects performed a randomized 6 second MVC for both knee flexors and extensors at 30 and 60 degrees of knee flexion with 2 minutes of rest between bouts. The subjects were instructed to produce force as “hard and fast as possible”. From these MVC’s, a toque-time graph which was used to calculate rate of torque development at various time periods (0-200ms at 50ms time intervals) and peak rate of torque development (RTDpeak). Countermovement jump testing was performed using a Vertec measuring device. The training protocol consisted of 2 sessions per week for 10 weeks (20 total) with a minimum of 48 hours of rest. Repetitions were performed with a 2 second concentric and eccentric phase. The weight was selected as the heaviest weight possible which allowed the subjects to complete 5 sets of 5 repetitions with 3 minutes of rest between sets. The program was progressed by adding .45-2.2 kg each training session. Posttest analysis revealed significant results for RTDpeak for the knee extensors (p<0.01), but not knee flexors (p=0.06). Dependent t-tests found significant pre-posttest increases in the training group for both knee extensors and flexors (p<0.01), no significant results were found in the control group. At the RTD50 time period, the training group exhibited significantly greater RTD for both knee extensors and flexors (p<0.01, p=0.02). Dependent t-tests found significant pre-posttest increases for the training group only (p<0.01). At the RTD200 time period, the training group exhibited significantly greater RTD200 for the knee extensors and flexors (p<0.01). Dependent t-tests noted significant results for pre-posttest for the training group for both the extensors and flexors (p<0.01). In the countermovement jump, dependent t-tests revealed significant results for the training group only (p<0.01). These results also correlated with knee flexor RTDpeak (r=0.37, p<0.01), RTD50 (r=0.30, p=0.03), and RTD200 (r=0.37, p<0.01). No correlations were found for knee extensor numbers. In summary, the deadlift exercise is an effective tool for novices to enhance their ability to generate force rapidly.
Munger, Archer, Leyva, Wong, Coburn, Costa, & Brown (2017), studied the acute effects of eccentric overload on concentric front squat rate of force development and performance. The study sample was 20 resistance training men with the mean age of 23.8 years with at least 1 year of resistance training experience. The study was a pre-postest design, with no control group. The first session consisted of a familiarization process and repetition maximum testing. Repetition max testing consisted of increasing weight until the subject failed to successfully complete the lift (front squat). ICC for front squat testing is between 0.75 and 0.80. Testing occurred 48-72 hours after baseline testing. The eccentric front squat protocol involved a 3 second eccentric phase, which was ensured by the use of a metronome. The eccentric phase used eccentric hooks, which allow the subject to use greater weight while weight during this phase. The intensities chosen were 105, 110, and 120% RM . The hooks are then released and the weight is reduced for the concentric phase. Subjects were encouraged to lift the barbell as fast as possible during the concentric phase. Intensity during the concentric phase was 90% RM. Two repetitions were performed for each intensity and 3 minutes of rest was provided between sets. Subjects were randomly assigned to begin with one of the 3 intensities. Rate of force development was measured using a force plate. No significant results were found for rate of force development in any of the conditions. Peak power was found to be significantly improved after a 120% eccentric squat (pre 2018.28 +/- 412.03 post 2,225 +/- 432.37 W). The results of this study suggest an acute supramaximal eccentric load does not enhance rate of force development but many improve peak power.
Lamont, Cramer, Bemben, Shehab, Anderson, & Bemben (2010), investigated the addition of whole-body vibration to squat training and its effects on force-time characteristics. The study consisted of 30 men between the ages of 18-30. They were randomly allocated to one of three groups: a squat training only (SQT, n=11), squat training plus vibration (SQTV, n=13), or a control group (CG, n=5). Subjects attended 2 familiarization sessions prior to the start of the experiment. Testing was performed during weeks 1, 3, and 7 and the dependent variables were maximal voluntary contraction (MVC) of a quarter squat, rate of force development (peak and time intervals of 30, 50, 80, 100, 150, and 250 ms), and 1 repetition maximum (1-RM) smith machine squat. The MVC quarter squat was assessed at a knee angle of 135 degrees. Subjects were instructed to push as hard and as fast as possible for a duration of 3.5 seconds for 4 trials with 90 seconds of rest between trials. These trials were also used to create a force-time curve to determine RFD. No instructions were provided for 1-RM testing. The training program consisted of 6 weeks of squat training using a periodized program focusing on strength for the first 3 weeks and power for the second 3 weeks. Training was conducted twice per week (12 sessions) with a 72 hour break between sessions. Intensity of exercise was between 55-90% RM for weeks 1-3 and 55-85% for weeks 4-6. The load was reduced the last three weeks to promote greater velocity during the exercise. Additionally, the second session during weeks 4-6 was considered a speed squat session where the subjects extended the weight all the way onto their toes. Four minutes of rest between sets was chosen to allow full recovery. Sets and reps were periodized according to intensity and ranged from 3 sets of 3 repetitions to 4 sets of 6 repetitions. Whole-body low frequency vibration was applied in a vertical orientation. Subjects held onto handles and stood on the vibration platform in the quarter squat position for 30 seconds with an amplitude of 2-4 mm prior to the first set of squat exercise. Three minutes of rest was provided after the vibration. Between sets, brief but higher amplitude vibration (4-6mm) was used at rest periods of 60 s, 120 s, and 180 s. Starting differences in RFDinitial limited the interpretation of the data and an ANCOVA was required to analyze the data. RFD30 was significantly reduced in the CG (-30.4%) at week 7 compared to both squat groups (p<0.05). No significant differences were found for RFD50. RFD100 found significant improvements for both CG (16.2%) and SQTV (9.6%). RFD 150 found improvements in the CG (20.6%) and SQTV (16.7%). No significant improvements were found in MVC from weeks 1-7. The results of this study provide a limited basis for vibration training. The data suggests that the application of vibration between sets may preferentially influence early time periods. However, the variability of the groups at baseline make interpretation of the data difficult.
Effects of ballistic training methods on rate of force development
Bogdanis, Tsoukos, Kaloheri, Terzis, Veligekas, & Brown (2017), compared unilateral and bilateral plyometric training on jumping performance and strength. The study consisted of 15 education students (age range: 18.2-25.8 years, 8 male, 7 female). They were randomly assigned to either a unilateral (n=7) or bilateral (n=8) training group. The study design was a repeated measures and baseline testing measured maximal isometric force and RFD, 1RM leg extension and curl, and countermovement and drop jump performance. Two familiarization sessions took place to reduce performance benefits derived from testing experience. Countermovement jump height was calculated using a force plate, which is a highly reliable method. The ICC of countermovement jumps was 0.99 (p<0.01). Drop jump height was calculated by the same method. The subjects dropped from a height of 30 cm, with either one or both legs, and then immediately jumped. Along with jump height, reactive strength index (a measure of explosiveness) was found by multiplying height x inverse of ground contact time. ICC for the drop jump were 0.95 for height, 0.96 for contact time, and 0.99 for the reactive strength index. Isometric strength and RFD were measured using a force plate mounted onto a rigid leg press with an approximate knee angle of 101 degrees. Subjects were instructed to push as fast and hard as possible for 4 seconds. RFD was recorded at 0-50, 100, 200, and 300 ms. ICC for RFD of single leg movements ranged from 0.873-0.98 and for bilateral from 0.951 to 0.990. The training intervention consisted of 2 sessions per week for 6 weeks (12 sessions) on non-consecutive days. Each group performed the same number of jumps and exercises with the only difference being the exercises being performed either unilateral or bilaterally. Rest was 1 minute between sets and 3 minutes between exercises. Statistically analysis revealed significant improvements for both groups in the countermovement jump. The unilateral group improved by 11.0±5.5% (p<0.001, d=0.59) and the bilateral group by 12.1±7.2% (p<0.001, d=1.01). Additionally, only the unilateral group significantly improved in unilateral countermovement jump performance (19.0±7.1%, p<0.001, d=1.17). No significant findings were noted for the drop jump and both group improved similarly (5% for bilateral and 9% for unilateral). For the reactive strength index, post-hoc testing revealed improvements in the unilateral group only (1.01±0.22 to 1.25±0.25 m•s-1, p=0.001, d=1.03). Isometric testing was significantly improved in both groups for bilateral testing. However, the unilateral group demonstrated significantly greater single leg strength (2-fold, d=1.22). For rate of force development, a 2-way ANOVA showed RFD50 was unchanged for the bilateral measurements. RFD100 was increased similarly between groups (d=0.66 for bilateral and d=1.05 for unilateral). The sum of left and right legs for RFD50 and RFD100 was improved only in the U group (d=0.77 and d=1.0, respectively. No interactions were found for RFD200 or RFD300. Leg strength was also increased similarly in both groups and the average strength increase for extension 1 RM being 30.8±14.7% (p<0.001, d=0.92) and for leg curl 1 RM being 22.2±14.1% (p=0.001, d=0.51). In summary, this study provides evidence that unilateral training provides performance benefits for both unilateral and bilateral tasks while bilateral training only improves bilateral performance. An additional and novel finding was the RFD improvements in the unilateral group only at early time periods.
Matavulj, Kukolj, Ugarkovic, Tihanyi, and Jaric (2001) examined the effects of plyometric training on rate of force development in junior basketball players. The subjects were 33 male junior basketball players (15-16 yo) whom had been participating in basketball for 5-8 years. They were randomly assigned to one of three groups (n=11). A control group, a 50 cm drop jump group (EG-50), and a 100 cm drop jump group (EG-100). The study was conducted in a pre/posttest design and the researchers were not blinded to the training program. Testing consisted of maximal jump height using an Ergojump apparatus, which is a force plate like tool. RFD and maximal strength were measured using a dynamometer with a digital display in a seated position with a knee angle of 110 degrees. The dynamometer was placed at the ankle to measure knee extensor contributions and at the shoulder to measure hip extensor contributions. Training took place during the season and each subject continued with normal basketball practice. The two experimental groups also participated in 3 training sessions per week for 6 weeks. Three sets of 10 repetitions were completed during the training sessions with 3 minutes of rest between sets. Both experimental groups improved vertical jump height, with EG-50 improving 4.8 cm and EG-100 improving 5.6 cm compared to control (p<0.017). No significant findings in any measurement were noted for the control group. Both EG-50 and EG-100 produced significant differences in RFD of the knee extensors when compared to control (post hoc: 14.72 for EG-50 and 8.42 for EG-100, p<0.017). No significant differences were found between EG-50 and EG-100. In conclusion, the addition of a low-volume brief plyometric program in-season provides an effective method to improve vertical jump height and rate of force development of the knee extensors in junior basketball players.
Behringer, Behlau, Montag, McCourt, & Mester, (2016) found low-intensity sprint training with blood flow restriction to effectively improve rate of force development. The study selected 25 healthy male sport students and randomly allocated them to either an experimental group (IG, n=12) or a control group (CG, n=12). The mean ages were 25.6 years and 21.7 years for the experimental and control groups. The training consisted of 6 weeks of sprint training twice per week (12 sessions) at 60-70% intensity, and were performed either with blood flow restriction (IG) or without blood flow restriction (CG). Blood flow restriction was applied via elastic wraps to the proximal thigh. Pressure was determined by using a rate of perceived exertion of 7 on a scale of 0-10. Dependent variables included 100m performance, maximal isometric leg press strength, rate of force development, and thigh muscle thickness. Biomarkers of testosterone, insulin-like growth factor-1, cortisol, lactate, and human growth hormone were also measured. 100 m sprint testing consisted of an all-out 100m sprint with a flying 50 cm start to remove reaction time. Time was electronically recorded on an indoor track. Leg press isometric strength and RFD were tested on a leg press with a force sensor which calculated a force-time curve. The knee angle during the test was 60 degrees and subjects were encouraged to achieve maximal effort. ICC for strength testing was 0.81 and for RFD 0.85. Muscle thickness was assessed using ultrasound and ICC of the rectus femoris was 0.85 and for the biceps femoris 0.79. Blood sampling occurred pre, 1 minute, 20 minutes, 120 minutes, and 24 hours after the first training session. Sprint times significantly improved in both the IG (p<0.001) and CG (p=0.007). IG sprint time decreased by M=0.38 ± 0.24 s and for CG by M=0.16 ± 0.17 s. No significant differences for sprint times were found between groups. In strength testing, a main effect of group was found with IG being 1.2 kN greater. For rate of force development, a significant group by time interaction was found for RFD values with significant results in the IG group only (24.1 ± 8.0 kN·s-130.1 ± 9.0* kN·s-1, p<0.05). Muscle thickness was significantly improved in the rectus femoris (26 ± 3 mm to 28 ± 3 mm, p<0.05) and biceps femoris (24 ± 6 mm to 26 ± 5mm, p<0.05) in the IG group only. Blood parameters found similar responses between groups for lactate, HGH concentrations, IGF, testosterone, and cortisol. In conclusion, it appears sprinting at low-intensities with blood flow restriction leads to greater improvements in RFD and muscle thickness than sprinting alone.
Mangine, Huet, Williamson, Bechke, Serafini, Bender, Hudy, & Townsend (2017), investigated the effects of a 5% body weight robotic resisted sprint protocol on sprinting kinetics and post activation potentiation. The study consisted of 23 division I basketball players (n=23, 10 males: 20.0 ± 1.7 years and 13 females: 20.0 ± 1.0 years). The subjects were participating in the same off-season program and were refrained from vigorous activity 48 hours prior to the study. Sprinting kinetics were measured via the 1080 Sprint, which is a portable cable resistance device which can manipulate the load from 1-15 kg and can extend out to 90m. After completing an extensive warm-up, athletes completed 4 sprints. One maximal 20m sprint without resistance followed by 3 sprints with the 1080 Sprint. The authors picked 20m as it is the most specific to the tested population (basketball). The three tested sprints were broken down as follows: the first and third sprint were completed with the minimal resistance of 1 kg, the second sprint was completed against 5% of the subjects bodyweight (to the nearest kg). A minimum of 3 minutes of rest between sprints was required with the averages being 5.43 ± 1.65 min between the first and second and 5.39 ± 1.16 min between the second and third. Athletes were allowed to use their preferred starting position. Data collected during the trials included sprint time, step length, step rate, peak and average force, velocity, and power. These variables were measured at distances of 5m, 10m, 15m, and 20m. Peak rate of force development was also calculated at these intervals using the equation change in force/change in time. Peak RFD was defined as the highest rate of change across all intervals. Resisted sprinting significantly reduced step length at all distance intervals (p<0.001): 5m (–31.1 3 ± 15.8%), 10m (–27.5 ± 17.7%), 15m (–25.8 ± 15.6%), and 20m (–21.0 ± 15.3%). The resisted condition also significantly increased sprint time at the 15m and 20m distances by 4.7 ± 5.2% (p < 0.001) and 3.4 ± 4.9% (p = 0.006). No changes were noted in step rate. Peak force, average force, peak power, average power, and rate of force development all demonstrated significantly greater values during the resisted sprint at all distance intervals (p<0.001). Peak velocity was reduced in the resisted sprint at 10m and 15 m and average velocity was reduced at the 15m and 20m intervals (p<0.05). The resisted sprint significantly enhanced rate of force development in the third sprint by 5.2 ± 7.1% when compared to the first. No other changes were found between the first and third sprint. The data from this study suggests resisted sprinting using 5% bodyweight fails to significantly improve sprint time or kinetics. It appears resisted sprinting does not elicit an appreciable post activation potentiation response, although it does have a minor effect on rate of force development.
Discussion/Conclusion
Overall, the current literature suggests that the type of training and the intent of the contraction plays a key role in improving rate of force development. For weight training methods, both fast concentric and eccentric methods improve rate of force development even when normalized for improvements in MVC (F.B.Oliveira, Rizatto, and Denadai 2013, A. Oliveira, Corvino, Caputo, Aagaard and Denadai, 2015). Eccentric training also enhances MVC, while fast-velocity concentric training does not. (A. Oliveira, Corvino, Caputo, Aagaard and Denadai, 2015). Fast velocity isometric training enhances MVC, but fails to improve RFD when normalized for this improvement (F. Oliveira, A. Oliveira, Rizatto, and Benedai, 2013). To summarize, it appears that dynamic contractions with the intent to produce force as fast and forcefully as possible offer unique benefits to RFD when compared to isometric training. In regards to resistance training variables, high intensity low-volume resistance training provides superior improvements in RFD when compared to high volume moderate-intensity training, despite the latter performing ~130% more training volume (Mangine, Hoffman, Wang, Gonzalez, Townsend, Wells, … Stout, 2016). For novices, the deadlift appears to be an effective exercise to improve the rate of force development (Thompson, Stock, Shields, Leura, Munayer, Mota…Olinghouse, 2015). Interestingly, the deadlift is an exercise which is primarily a concentric movement performed from a stand still. It can be hypothesized this method may be superior for enhancing the nervous system’s ability to produce doublets in an attempt to overcome the initial weight. This improvement in doublets could theoretically be the mechanism in which concentric exercise improve RFD. Both studies which examined primarily concentric weight training interventions found significant effects on RFD (F.B.Oliveira, Rizatto, and Denadai 2013, Thompson, Stock, Shields, Leura, Munayer, Mota…Olinghouse, 2015). The addition of vibration to exercise interventions appears to offer only a small to negligent benefit in RFD (Lamont, Cramer, Bemben, Shehab, Anderson, & Bemben, 2010). The data concerning vibration training included in this review was difficult to interpret secondary to the baseline variation between test groups. In addition, acute supramaximal eccentric exercise failed to improve RFD (Munger, Archer, Leyva, Wong, Coburn, Costa, & Brown, 2017). This may be due to the concentric phase being performed with too heavy a weight (90% RM), which prevents explosive lower body performance and high levels of velocity. It would be interesting to see the effects on a lighter concentric phase, which allows individuals to generate greater lifting velocities.
Ballistic exercises in general produced more consistent results than weight training interventions. This may be due to the high velocity nature of this style of exercise. The addition of a low volume plyometric program can successfully improve RFD and jump height with little difference between drop heights (Matavulj, Kukolj, Ugarkovic, Tihanyi, and Jaric, 2001). A unilateral plyometric program enhanced both uni and bilateral performance and rate of force development (Bogdanis, Tsoukos, Kaloheri, Terzis, Veligekas, & Brown, 2017). Additionally, the unilateral plyometric group had a greater transfer of training effect than the bilateral training group. On the contrary, the bilateral training failed to transfer to unilateral performance. This is important for exercise experts as most sporting actions are unilateral, while the most common training methods are bilateral (squat, deadlift). Performing more unilateral exercises will help ensure transfer of training. Low-intensity sprinting with blood flow restriction also appears a viable option to improve RFD and sprint times (Behringer, Behlau, Montag, McCourt, & Mester, 2016). Sprinting involves minimal ground contact times and the ability to produce force into the ground rapidly. On the surface, sprinting would appear to be a key training intervention for RFD. Lastly, the acute effects of resisted sprinting fails to elicit performance benefits from post-activation potentiation (Mangine, Huet, Williamson, Bechke, Serafini, Bender, Hudy, & Townsend, 2017). Sprint times and kinetics remained unchanged following a 5% bodyweight resisted sprint. This could be for a number of reasons including the relatively light resistance used, or an imbalance between fatigue and recovery between bouts. It does appear resisted sprint offers a small acute benefit in peak rate of force development.
Future areas for research include performing the high-volume moderate intensity training with the intent to perform each rep as fast and forcefully as possible. It is conceivable that the higher intensity group was forced to perform each rep in this manner, while the moderate intensity group may have not. Another interesting study would be to combine high intensity low-volume training with a low-volume plyometric group. Combining these two training modalities may further enhance RFD and athletic performance. In conclusion, multiple methods can selectively improve RFD. The usage of this knowledge can help strength and conditioning professionals enhance athletic performance and improve their periodization models.
References
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Bogdanis, G. C., Tsoukos, A., Kaloheri, O., Terzis, G., Veligekas, P., & Brown, L. E. (2017). Comparison between Unilateral and Bilateral Plyometric Training on Single and Double Leg Jumping Performance and Strength. Journal of Strength and Conditioning Research, 1. doi:10.1519/jsc.0000000000001962
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