This brief review encompasses the role of maximal strength and rate of force development in the production of muscular power. It begins with the investigation of power output and its importance for sport. After this basis for power production, this review examines both maximal strength and rate of force development effects on the development of optimal power output. Finally, a rational why maximizing rate of force development during the competition season to achieve success in sport is provided.

Typical rehabilitation strategies and performance tests after knee surgery are often based on peak lower extremity strength. However, people rarely generate maximal knee force in both daily and sports activities, which are characterized by brief periods of rapid muscle activation and relaxation. Thus, the ability to rapidly develop or modulate force may be more meaningful and more relevant to function. It is unclear how knee surgery influences the neuromuscular mechanisms controlling the ability to rapidly develop leg muscle force and produce power, or the functional relevance of these characterizations of muscle performance in relation to injury, surgery, and recovery. The primary purpose of this collection of studies was to assess rapid quadriceps muscle activation and lower extremity force production in people undergoing arthroscopic knee surgery for meniscal debridement and anterior cruciate ligament (ACL) reconstruction. People undergoing arthroscopic partial meniscectomy (APM) presented with significant deficits in knee extensor rate of torque development (RTD), leg press power, and rapid quadriceps muscle activation both prior to and in the initial month following surgery. Subjective knee function was significantly correlated with RTD variables but not with peak strength or quadriceps volume. Limitations in the ability to rapidly activate the involved quadriceps suggests that impaired centrally mediated neural function of the involved quadriceps may limit RTD and lower extremity power post-surgery. Next, the speed and intensity of quadriceps exercise performed in the early post-surgical period of patients post-APM and the relationships between training parameters, strength, quadriceps RTD, and subjective knee function were investigated. Subjects performed high intensity quadriceps contractions 2-3x/week in the first month following surgery. All subjects increased quadriceps strength, but people who trained with greater RTD following APM demonstrated greater improvements in RTD and had better patient-based outcomes scores than those who trained with a slower rate of torque rise. Finally, power and rate of force development (RFD) in people ≤ 1 year following ACL reconstruction were evaluated along with movement biomechanics, typical clinical measures of readiness to return to activity, and patient-based outcomes. Significant side-to-side asymmetries in quadriceps strength, RFD, leg press strength and power, and knee joint kinetics were noted. Deficits in voluntary quadriceps strength paralleled the deficits in early phase RFD, indicating that in this population RFD was limited by the intrinsic properties and force production capacity of the quadriceps, not the ability to rapidly activate the muscle. However, strong to very strong correlations were found between quadriceps RFD, movement biomechanics and subjective knee function, which were predominantly stronger than the correlations with peak quadriceps strength. Leg press strength, power, and acceleration were very strongly correlated with movement biomechanics and subjective knee function. In summary, this series of studies provides important insight into the neuromuscular mechanisms related to rapid lower extremity force development and muscle activation in the context of knee joint injury and recovery after arthroscopic knee surgery. Collectively, this work suggests that the inability to quickly develop or modulate quadriceps force may have significant functional consequences, and that rehabilitation efforts following arthroscopic knee surgery to incorporate both specific dosage of and earlier performance of rapid leg muscle contractions should be explored.

The research described in this thesis examined age- and strength training-related changes in Achilles tendon stiffness and plantarflexor force production in prepubertal children. The measurement of both Achilles tendon stiffness and muscular force production requires in vivo moment arm lengths to be known. Currently, this is possible only by using expensive and time-consuming medical imaging methodologies. Therefore, the predictability of the Achilles tendon moment arm from surface anthropometric measurements was assessed in the first experimental study (Chapter 3). The results demonstrated that a combination of foot length and the distance between the calcaneal tuberosity and 1st metatarsal head could explain 49% of the variability in Achilles tendon moment arm length in 5 – 12 year-old children. This was considered to be unacceptable for further use, thus an ultrasound-based method was decided upon for obtaining moment arm length in subsequent experimental studies. In the second and third experimental studies (Chapters 4 and 5), age-related changes in tendon mechanical and structural properties were documented and their relationship with changes in force production ability were examined in prepubertal children (5 – 12 years) and adult men and women. In Chapter 4, Achilles tendon stiffness was shown to increase with age through to adulthood, and that changes in tendon stiffness were strongly and independently associated with body mass (R2 = 0.58) and peak force production capacity (R2 = 0.51),which may provide the tendon with an increasing mechanical stimulus for growth and microadaptation. These increases in tendon stiffness were associated with a greater increase in tendon CSA (~105%) than that found for tendon length (~60%), in addition to an increase in Young’s modulus (~139%), suggesting that gross increases in tendon size as well as changes in its microstructure underpinned the increase in stiffness. In Chapter 5, the relationships between Achilles tendon stiffness and both electro-mechanical delay (EMD) and rate of force development (RFD) were determined during maximal isometric plantarflexion contractions. Moderate correlations were found between tendon stiffness and both EMD (r = -0.66) and RFD (r = 0.58). RFD was significantly better predicted when muscle activation (estimated as the rate of EMG rise) was included in a regression model. These data clearly show that increases in tendon stiffness with age through to adulthood are associated with decreases in EMD and increases in RFD, and that the rate of muscle activation has an additional influence on RFD during growth. Given that 1) Achilles tendon stiffness was lower in children than adults, 2) this lower stiffness was associated with a longer EMD and slower RFD, and 3) that strength training in adults had previously been shown to increase tendon stiffness and RFD, the adaptability of the developing Achilles tendon to a resistance training programme, and consequence of the potential changes on force production capacity were examined in the final experimental study (Chapter 6). Significant increases in Achilles tendon stiffness and Young’s modulus were found after 10 weeks of twice-weekly plantarflexor strength training in 8-9 year-old boys and girls, which demonstrates that the larger muscle force production provided a sufficient stimulus for tendon microadaptation. The training also resulted in a decrease in EMD, which was moderately correlated with the change in tendon stiffness (r = 55), but no change in RFD. Thus, the increasing tendon stiffness with training was associated with a decreasing EMD, but had no detectable effect on RFD. This would likely have a significant effect on the performance of tasks requiring rapid muscle force production. Together, the results of the present series of investigations demonstrate that the tendon loading experienced from both normal ageing and overloading (strength training) can increase tendon stiffness in children, and that these changes have a detectable effect on rapid force production.

The purpose of the study was to explore and determine kinetic and kinematic variables that related to D-I male sprinters maximal running velocity performance. The current study was separated into 3 individual chapters: 1.) Kinematic analysis magnitude of acceleration for braking and propulsion phases during foot contact phase at maximal speed sprinting; 2.) Using kinetic isometric mid-thigh pull variables to predict D-I male sprinters’ 60m performance; 3.) Relationship of whole and lower body angular momentum cancellation during terminal swing phase to sprint performance. Methods: for sprint measurement all the athletes were participated 2 trials of 100% effort running through 60 meters. The sprint time was measured by an electronic timing gate system. The electronic timing gate system was placed at every 10 meter intervals from the start line for 60 m. Six cameras were placed between 50 m and 60 m for kinematic data collection and analysis. Volume captured by the cameras is 7.5 m long, 1.2 m wide, and 1.95 m high. Reflective markers were attached on the body landmarks based on Vicon Nexus full body plugin model. The strength assessments were performed in a customized power rack, and kinetic values were collected via a dual force plate setup (2 separate 91 cm x 45.5 cm force plates, Roughdeck HP, Rice Lake, WI). The position for each isometric pull was established before each trial using goniometry, with each bar height corresponding to a 125±5º knee angle and a near-vertical trunk position. Results: current study partially support previous assumption that fast sprinters can minimize braking phase during foot contact phase when they are running maximal velocity. However, those minimizing effects did not impact maximal running velocity performance. Second, the study showed that fast sprinters can produce greater force during a short period of time than slower sprinters. Moreover, a certain trend of statistical significance was observed from the third study that angular momentum cancellation between lower bodies at frontal plane may be related to maximal running velocity performance. Discussion: the current study confirmed that fast sprinters can produce greater force in a short period time. However, the current study did not show statistical significance of angular momenta cancellation and sprint performance. Only a level of trend was observed. Thus, further study should examine sprinters with different training background, especially elite level sprinters is definitely needed.

Força máxima (TF) e potência (TP) são métodos de treinamento considerados distintos, na prática profissional e em diversos designs experimentais. O presente estudo testou a capacidade destes métodos promoverem o aumento do desempenho, assim como a similaridade das adaptações entre os métodos. Trinta e sete sujeitos foram divididos nos grupos: força (TF), potência (TP) e controle (C), sendo submetidos a oito semanas de treinamento nas seguintes zonas: TF (4-10 RM) e TP (30-60% 1RM). Os resultados significantes foram: força dinâmica máxima TF de 145,3 (±17,1) para 178,5 (±18,8) kg, TP de 147,2 (±16,8) para 171,6 (±19,9) kg; pico de força na contração voluntária isométrica máxima (CVIM) TF de 2240,52 (±448,76) para 2651,82 (±700,22) N, TP de 2249,86 (±427,95) para 2674,80 (±507,68) N; salto vertical a partir da posição de semi-agachamento (SJ) TF de 31,35 (±4,63) para 37,18 (±4,74) cm, TP de 34,44 (±3,90) para 39,61 (±4,70) cm. Apenas o TP gerou aumento no salto com contra-movimento (CMJ) de 35,52 (±4,43) para 38,50 (±4,34) cm. Nenhum dos protocolos promoveu o aumento do sinal eletromiográfico, seja na CVIM ou nos saltos. Verificou-se efeito principal para deslocamento do centro de gravidade, torque de joelho e quadril no SJ, assim como para o deslocamento excêntrico no CMJ. Observou-se similaridade entre os grupos em diversas variáveis analisadas, assim como a possível transferência coordenativa do TP para o CMJ. Assim, força máxima e potência parecem constituir estímulos de treinamento equivalentes em muitos aspectos e por isso, os padrões de especificidade atribuídos a ambos devem ser reconsiderados / Strength and power are considered different training methods in promoting neuromuscular adaptations in practice and in several research designs as well. In the present research, the efficacy of these methods in improving performance and resultant neural adaptations in some motor tasks was investigated. Thirty sevens subjects were divided in groups: strength (TF), power (TP) and control (C) and submited to eight weeks of training in different zones: TF (4-10 RM) and TP (30%-60% 1RM). Results that reached significance were the following, pre and pos-test, respectively: Maximum dynamic strength TF:145,3 (±17,1) and 178,5(±18,8), TP:147,2 (±16,8) and 171,6 (±19,9). Peak force in maximum isometric voluntary contraction (MIVC) TF: 2240,52 (±448,76) and 2651,82 (±700,22), TP: 2249,86 (±427,95) and 2674,80 (±507,68). Squat jump (SJ) TF: 31,35 (±4,63) and 37,18 (±4,74), TP: 34,44 (±3,90) and 39,61 (±4,70). In countermovement jump (CMJ) only TP improved: 35,52 (±4,43) and 38,50 (±4,34). No method could improve electromiographical signal. A main effect was noticed for center of mass displacement, knee and hip moments in SJ and eccentric displacement in CMJ. Similar results for many parameters analysed could be observed. The results indicate a possible transference from TP to CMJ as well. This way, strength and power can be considered equivalent in promoting performance in many tasks. Therefore, specificity patterns between strength and power should be reconsidered

Força máxima (TF) e potência (TP) são métodos de treinamento considerados distintos, na prática profissional e em diversos designs experimentais. O presente estudo testou a capacidade destes métodos promoverem o aumento do desempenho, assim como a similaridade das adaptações entre os métodos. Trinta e sete sujeitos foram divididos nos grupos: força (TF), potência (TP) e controle (C), sendo submetidos a oito semanas de treinamento nas seguintes zonas: TF (4-10 RM) e TP (30-60% 1RM). Os resultados significantes foram: força dinâmica máxima TF de 145,3 (±17,1) para 178,5 (±18,8) kg, TP de 147,2 (±16,8) para 171,6 (±19,9) kg; pico de força na contração voluntária isométrica máxima (CVIM) TF de 2240,52 (±448,76) para 2651,82 (±700,22) N, TP de 2249,86 (±427,95) para 2674,80 (±507,68) N; salto vertical a partir da posição de semi-agachamento (SJ) TF de 31,35 (±4,63) para 37,18 (±4,74) cm, TP de 34,44 (±3,90) para 39,61 (±4,70) cm. Apenas o TP gerou aumento no salto com contra-movimento (CMJ) de 35,52 (±4,43) para 38,50 (±4,34) cm. Nenhum dos protocolos promoveu o aumento do sinal eletromiográfico, seja na CVIM ou nos saltos. Verificou-se efeito principal para deslocamento do centro de gravidade, torque de joelho e quadril no SJ, assim como para o deslocamento excêntrico no CMJ. Observou-se similaridade entre os grupos em diversas variáveis analisadas, assim como a possível transferência coordenativa do TP para o CMJ. Assim, força máxima e potência parecem constituir estímulos de treinamento equivalentes em muitos aspectos e por isso, os padrões de especificidade atribuídos a ambos devem ser reconsiderados / Strength and power are considered different training methods in promoting neuromuscular adaptations in practice and in several research designs as well. In the present research, the efficacy of these methods in improving performance and resultant neural adaptations in some motor tasks was investigated. Thirty sevens subjects were divided in groups: strength (TF), power (TP) and control (C) and submited to eight weeks of training in different zones: TF (4-10 RM) and TP (30%-60% 1RM). Results that reached significance were the following, pre and pos-test, respectively: Maximum dynamic strength TF:145,3 (±17,1) and 178,5(±18,8), TP:147,2 (±16,8) and 171,6 (±19,9). Peak force in maximum isometric voluntary contraction (MIVC) TF: 2240,52 (±448,76) and 2651,82 (±700,22), TP: 2249,86 (±427,95) and 2674,80 (±507,68). Squat jump (SJ) TF: 31,35 (±4,63) and 37,18 (±4,74), TP: 34,44 (±3,90) and 39,61 (±4,70). In countermovement jump (CMJ) only TP improved: 35,52 (±4,43) and 38,50 (±4,34). No method could improve electromiographical signal. A main effect was noticed for center of mass displacement, knee and hip moments in SJ and eccentric displacement in CMJ. Similar results for many parameters analysed could be observed. The results indicate a possible transference from TP to CMJ as well. This way, strength and power can be considered equivalent in promoting performance in many tasks. Therefore, specificity patterns between strength and power should be reconsidered

The purpose of this study was to determine the acute effects of stretching and local vibration on flexibility and explosive strength in competitive female gymnasts. Flexibility was measured in the forward-split position and jump characteristics were recorded using a force plate. Analysis included flight time (FT), jump height (JH), peak force (PF), instantaneous forces, and rates of force development (RFDs). Randomly assigned and counterbalanced groups were: simultaneous vibration-stretching (VS) (n=22), stretching-only (n=7), and vibration-only (n=8). VS showed statistically greater measures of flexibility in both the right and left leg, favored and non-favored legs pre- versus post-treatment. Vibration-only group resulted in statistically greater right forward-split flexibility and non-favored leg flexibility. There were no statistical differences in JH, FT, PF, instantaneous forces, or RFDs in the VS, stretching-only, and vibration-only groups' pre- versus post-treatment tests. The conclusion was simultaneous vibration-stretching greatly increased flexibility while not altering explosive strength.

The purposes of this dissertation were three-fold. The first was to identify the approximate distances characterizing early-, mid-, and late-acceleration in a population of Division I men’s collegiate soccer players. The secondary purpose was to investigate the relationships between various strength-power variables and key sprint characteristics during early-, mid-, and late-acceleration in a population of Division I men’s soccer players. The final purpose of this dissertation was to compare the spatiotemporal characteristics of “strong” versus “weak” and “more powerful” versus “less powerful” Division I men’s soccer players during early-, mid-, and late- acceleration. The following are the major findings of this dissertation. The early-, mid-, and late-acceleration zones within this sport population coincide with distances of approximately 0-2.5, 2.5-6, and 6-12m, respectively. Peak power (PP) and rate of force development (RFD) at 90ms appear to be strongly related to shorter ground contact times in each of these zones, while PP and RFD at 200 and 250ms showed strong relationships with step frequency during mid-acceleration. Not surprisingly, athletes who were characterized as “strong” or demonstrated “higher power outputs” appeared to achieve greater sprint velocity by expressing higher step frequency, particularly during mid-acceleration, as well as abbreviated ground contact times across each sub-section of acceleration. These results support the importance of developing high levels of maximal strength, PP, and RFD to enhance sprint acceleration. Additionally, these findings may also be used to strategically integrate speed development and resistance training practices into the annual training plan. The amalgamation of these training variables may allow practitioners to better manage fatigue and elicit desired performance adaptations at the appropriate times of the training year.

The purpose of this investigation was to explore the phenotypic and performance outcomes associated with ACTN3 and ACE polymorphisms. Ten trained men (age = 25.8 ± 3.0 years, height = 183.3 ± 4.1 cm, body mass = 92.3 ± 9.3 kg, and back squat to body mass ratio = 1.8 ± 0.3) participated. Blood samples were analyzed to determine ACTN3 and ACE polymorphisms. Standing ultrasonography images of the vastus lateralis (VL) were collected to determine whole muscle cross-sectional area (CSA-M), and a percutaneous muscle biopsy of the VL was collected to determine type I–specific CSA (CSA-T1), type II–specific CSA (CSA-T2), and type II to type I CSA ratio (CSA-R). Isometric squats were performed on force platforms with data used to determine peak force (IPF), allometrically scaled peak force (IPFa), and rate of force development (RFD) at various timepoints. One repetition maximum back squats were performed, whereby allometrically scaled dynamic strength (DSa) was determined. Cohen's d effect sizes revealed ACTN3 RR and ACE DD tended to result in greater CSA-M but differ in how they contribute to performance. ACTN3 RR's influence seems to be in the type II fibers, altering maximal strength, and ACE DD may influence RFD capabilities through a favorable CSA-R. Although the findings of the current investigation are limited by the sample size, the findings demonstrate the potential influence of ACTN3 and ACE polymorphisms on isometric and dynamic strength testing. This study may serve as a framework to generate hypotheses regarding the effect of genetics on performance.

Power-generating capacity should be a primary training outcome for football athletes. The ability to be explosive and use high levels of strength seems to differentiate between athletes and teams. Developing training interventions that can improve both strength- and power-generating capacity would therefore be considered a paramount endeavor when attempting to optimize the physiological and performance adaptations necessary for competitive success. Too often, strength and conditioning coaches forget that the foundation of powergenerating capacity is in fact high levels of muscular strength. When the development of strength is minimized or excluded from the training plan, the ability to express high-power outputs is compromised. In addition, a failure to use sequenced and integrated training programs decreases the possibility of successfully increasing strength- and power-generating capacity, thus decreasing the potential for competitive success. Therefore, this brief review attempts to explain how strength- and powergenerating capacity can be enhanced to increase the potential for developing the physiological and performance foundation necessary for competitive success with the football athlete.