Purpose: to examine the relationship between isometric force characteristics (IF) and vertical jump height under various loading conditions. Sixty-three collegiate athletes participated in this investigation. Athletes performed static jump (SJ) and countermovement jumps (CMJ) with 0 and 20kg, and isometric mid-thigh pulls on a force plate. Force-time curve analysis was conducted for each isometric pull and jump to determine force related characteristics. Jump height (JH) was derived from flight time. Isometric forces were normalized using allometric scaling: absolute force/ (body mass(kg)0.67)= IPFa. Results: There was a strong positive correlation between isometric peak force and isometric rate of force development (IRFD). Stronger athletes had smaller decrements in jump height with additional loading. Conclusion: The ability to produce higher peak and instantaneous forces and IRFD is related to JH and smaller differences between weighted and unweighted jumps. A weighted jump may be a practical method of assessing relative strength levels.

The purpose of this study was to observe physiological metrics relative to training-induced adaptations in conjunction with laboratory- and competition-based performances in a super-heavyweight weightlifter recovering from a meniscus injury. A retrospective analysis was conducted on a collegiate level male weightlifter (23.2 yrs; 131.9 kg; 187.3 cm) over the course of 21-weeks post-meniscus surgery. Body mass, body fat percentage, hydration status, vastus lateralis muscle cross-sectional area, jump performance, and isometric midthigh pull were regularly assessed as part of an ongoing athlete monitoring program. Pre-injury baseline (T0) measurements were collected relative to a major national competition (COMP1). Post-injury measurements took place at the end of sequential training blocks: strength-endurance training block 1 (T1), basic strength block 2 (T2), and transmutation block 3 (T3). The final measurement session (T4) was conducted three-days post-local competition (COMP2). Only statistically significant increases were observed from T0-T4 for muscle CSA (p=0.0367), isometric peak force (pp=0.0367), and rate of force development at 250ms (p=.0367). While non-significant changes were observed for jumping performance, jump height and net impulse did, however, return to baseline. Competition based performances also showed marked improvements from pre-to-post injury via an increase in weightlifting total (3.2%∆, +9kg) and Sinclair score (1.8%∆, +5.3au). Thus, based on these findings, implementing an evidence-based training program along with a sound athlete monitoring protocol can aid with reducing an athlete’s return-to-train timeline while improving physiological, laboratory- and competition-based performance outcomes.

Neural activation is thought to be essential for the expression of maximal muscle performance, but the exact contribution of neural mechanisms such as the level of agonist, antagonist and stabiliser muscle activation to muscle strength is not fully understood. Explosive neuromuscular performance, including the ability to initiate (the electromechanical delay, EMD) and develop force rapidly (termed, rate of force development, RFD) are considered essential for the performance of explosive sporting tasks and joint stabilisation and thus injury avoidance. The thesis aimed to improve our understanding of the contribution of neural factors to muscle performance, with a specific focus on explosive neuromuscular performance. The work in this thesis utilised a range of approaches to achieve this aim. Initially, the association between muscle activation and rate of force development and EMD was established. Comparison of unilateral and bilateral actions was then undertaken. Finally interventions with the aim to both negatively affect and improve muscle strength, which included fatigue and resistance training (RT), respectively was undertaken and the neural contributions to changes in performance established. Agonist activation during the early phase of voluntary force production was shown to be an important determinant of voluntary EMD, explaining 41% of its inter-individual variability. Agonist activation was an important determinant of early, but not late phase RFD. Use of bilateral actions resulted in a reduction in explosive strength, which was thought to be due to differences in postural stability between unilateral and bilateral strength tasks. The level of stabiliser activation was strongly related to the level of agonist activation during the early phase of explosive force development and had a high association with explosive force production. Task-specific adaptations following isoinertial RT, specifically, the greater increase in isoinertial lifting strength than maximal isometric strength were due to training-specific changes in the level of agonist activation. High-intensity fatigue achieved a more substantial decline in explosive than maximal isometric strength, and this was postulated to be due to neural mechanisms, specifically decreased agonist activation. This work provides an in depth analysis of the neural contributions to maximal muscle performance.

Apesar das perdas provocadas pela sarcopenia, o sistema neuromuscular do idoso ainda mantém parte da sua plasticidade. No entanto, as adaptações promovidas pelos treinamentos de força (TF) e de potência (TP) não foram totalmente elucidadas, assim como se existem diferenças entre essas adaptações nessa população. Para responder tais questões, 43 idosos (63,8 ± 4,0 anos; 67,2 ±13,4kg e 160,2 ±8,4cm), inexperientes em treinamento com pesos e independentes participaram desse estudo. Os voluntários foram distribuídos em três grupos: GF (n= 14; 70 a 90% de 1RM), GP (n= 16; 30 a 50% de 1RM) e GC (n= 13, não treinou). Durante 16 semanas o GF e o GP realizaram duas sessões de treino semanalmente. Os resultados significantes foram: aumento de 42,7% em GF e 33,8% em GP no teste de 1RM (leg press) e 31% em GF e 25,4% em GP (chest press); aumento de 6% em GF e 3,6% em GP na ASTq; aumento de 22,4% em GF e 17,1% em GP na CVIM e uma diminuição de 28% em GF e 32% em GP no REM. Não houve diferenças significativas entre GF e GP nas variáveis analisadas. Nenhum dos grupos apresentou aumento no sinal eletromiográfico nem na TDF. Não houve alteração significativa na funcionalidade. Portanto, ainda que com características distintas, o TF e o TP são similares em relação às adaptações analisadas, equiparando-se como estratégias de treinamento eficazes no combate à sarcopenia e seus efeitos / In spite of sarcopenia-induced losses, elderly peoples neuromuscular system keeps its plasticity. However, strength and power training-induced adaptations have not been completely elucidated. It also unknown if these adaptations are related to elderly functionality. Fourty three healthy and independent old men and women (63.8 ± 4.0 yrs; 67.2 ±13.4kg e 160.2 ±8.4cm) with no resistance training experience volunteered for this study. Participants were randomly distributed into three groups: GF (n= 14; 70 - 90%-1RM), GP (n= 16; 30 - 50%-1RM) e GC (n= 13, no training). GF and GP trained twice a week for 16 weeks. Leg-press (42.7% in GF and 33.8% in GP) and chest-press 1-RM (31% in GF and 25.4% in GP), quadriceps cross sectional area (6% in GF and 3.6% in GP), maximal voluntary isometric contraction (22.4% in GF and 17.1% in GP) were significantly increased in both groups. Electromechanical delay decreased 28% in GF and 32% in GP. There were no significant differences between groups. EMG and rate of force development did not change throughout the training period. Only main effect of time was observed for the functional tests. These results suggest that even with different characteristics, both strength and power training induce similar neuromuscular adaptations. Thus, both training regimens are equally effective in preventing and treating sarcopenia

Abstract available in the Annual Coaches and Sport Science College.

The current investigation was an examination of the repetition-to-repetition magnitudes and changes in kinetic and kinematic characteristics of the back squat using accentuated eccentric loading (AEL) and cluster sets. Trained male subjects (age = 26.1 ± 4.1 years, height = 183.5 ± 4.3 cm, body mass = 92.5 ± 10.5 kg, back squat to body mass ratio = 1.8 ± 0.3) completed four load condition sessions, each consisting of three sets of five repetitions of either traditionally loaded straight sets (TL), traditionally loaded cluster sets (TLC), AEL cluster sets (AEC), and AEL straight sets where only the initial repetition had eccentric overload (AEL1). Eccentric overload was applied using weight releasers, creating a total eccentric load equivalent to 105% of concentric one repetition maximum (1RM). Concentric load was 80% 1RM for all load conditions. Using straight sets (TL and AEL1) tended to decrease peak power (PP) (d = −1.90 to −0.76), concentric rate of force development (RFDCON) (d = −1.59 to −0.27), and average velocity (MV) (d = −3.91 to −1.29), with moderate decreases in MV using cluster sets (d= −0.81 to −0.62). Greater magnitude eccentric rate of force development (RFDECC) was observed using AEC at repetition three (R3) and five (R5) compared to all load conditions (d = 0.21–0.65). Large within-condition changes in RFDECC from repetition one to repetition three (∆REP1–3) were present using AEL1 (d = 1.51), demonstrating that RFDECC remained elevated for at least three repetitions despite overload only present on the initial repetition. Overall, cluster sets appear to permit higher magnitude and improved maintenance of concentric outputs throughout a set. Eccentric overload with the loading protocol used in the current study does not appear to potentiate concentric output regardless of set configuration but may cause greater RFDECCcompared to traditional loading

Neuromuscular explosive strength (defined as rate of force development; RFD) is considered important during explosive functional human movements; however this association has been poorly documented. It is also unclear how different variants of strength training may influence RFD and its neuromuscular determinants. Furthermore, RFD has typically been measured in isometric situations, but how it is influenced by the types of contraction (isometric, concentric, eccentric) is unknown. This thesis compared neuromuscular function in explosive power athletes (athletes) and untrained controls, and assessed the relationship between RFD in isometric squats with sprint and jump performance. The athletes achieved a greater RFD normalised to maximum strength (+74%) during the initial phase of explosive contractions, due to greater agonist activation (+71%) in this time. Furthermore, there were strong correlations (r2 = 0.39) between normalised RFD in the initial phase of explosive squats and sprint performance, and between later phase absolute explosive force and jump height (r2 = 0.37), confirming an association between explosive athletic performance and RFD. This thesis also assessed the differential effects of short-term (4 weeks) training for maximum vs. explosive strength, and whilst the former increased maximum strength (+20%) it had no effect on RFD. In contrast explosive strength training improved explosive force production over short (first 50 ms; +70%) and long (>50 ms; +15%) time periods, due to improved agonist activation (+65%) and maximum strength (+11%), respectively. Explosive strength training therefore appears to have greater functional benefits than maximum strength training. Finally, the influence of contraction type on RFD was assessed, and the results provided unique evidence that explosive concentric contractions are 60% more effective at utilising the available force capacity of the muscle, that was explained by superior agonist activation. This work provides a comprehensive analysis of the association between athletic performance and RFD, the differential effects of maximum vs. explosive strength training, and the influence of contraction type on the capacity for RFD.

The purpose of this investigation was to assess the between-day reliability of selected force-time curve indices and the activity onset of selected neck muscles in the performance of maximal, isometric contractions in five different directions. The measures extracted are deemed important for future investigations aimed at exploring the role of cervical musculature in reduction of concussion occurrences in sports. Twenty eight physically active male participants performed two testing sessions separated by 7-8 days. In each testing session, force and surface electromyography (EMG) data were recorded simultaneously in a custom-made testing apparatus whilst subjects performed four randomized maximal isometric efforts in extension, flexion, and left and right lateral bending and protraction. The variables examined were the peak force, rate of force development (RFD), time to 50% of peak force and bilateral activity onset of the splenius capitis, upper trapezius, and sternocleidomastoid. For all variables, reliability was assessed by: 1) difference scores between the testing sessions and corresponding 95% confidence intervals; 2) standard error of measurement (SEM), expressed in either the original units of measurement, or as a coefficient of variation; and, 3) Intraclass correlation coefficients (ICC). The results indicated that for all variables, in all testing directions, no differences in scores were observed between the first and second testing sessions. The precision of measurement for all measures, barring muscle onsets obtained in protraction, was deemed acceptable for future clinical application. ICC score ranges for force-time curve-based measurements were high (< 0.90), while for muscle onsets, the ICC ranges are low to moderate (0.23 -0.79). Based on these results, it was concluded that, in highly active male participants, a dedicated familiarization session for the elimination of potential learning effects is not required. In addition, for the majority of testing directions, the force-time curve-based variables as well as muscle activity onsets are recorded with a sufficiently high level of precision, which make them prime candidates for utilization in future investigations concerned with quantitative assessment of cervical musculature function. / Thesis (Master, Kinesiology & Health Studies) -- Queen's University, 2009-09-23 01:23:12.324

Muscle performance is partially a consequence of its recent contractile history. Postactivation potentiation (PAP) can occur after muscle contractions and leads to enhanced neuromuscular performance. The purpose of this dissertation was to explain the relationship between muscle factors (twitch potentiation, TP) and neural factors (reflex potentiation, RP) contributing to overall PAP following a non-fatiguing volitional muscle contraction. The tibial nerves of fifteen resistance trained volunteers (eleven men, four women) were stimulated intermittently at supramaximal (Mmax) and submaximal (Hmax) intensities for 20 minutes on separate days under three conditions: rest (Control); after a after a 10 second maximum voluntary isometric contraction (MVIC) of the plantarflexors; and after a low frequency fatigue protocol prior to the MVIC. Plantarflexion isometric torque and rate of force development (RFD), and soleus and gastrocnemius EMG Hmax/Mmax ratios, were analyzed. Both experimental conditions resulted in TP at 10 seconds post-MVIC compared to the control condition. The two experimental conditions were not different for any measure. Torque and RFD at Hmax (overall PAP) were highest at 3 and 4.5 minutes post MVIC, respectively, but were not significantly different from the control condition. EMG values generally were insignificantly increased in the experimental conditions versus the control condition. Mmax torque and RFD significantly contributed to Hmax torque and RFD at 20 seconds, Hmax peak, and 20 minute post-MVIC time points. The soleus significantly contributed to Hmax torque at 20 seconds and 20 minutes post-MVIC, and Hmax RFD at 20 seconds, 4.5 minutes, and 20 minutes post-MVIC. The results of this study suggest that both muscle and neural factors play a significant role in overall PAP, and that neural factors may play a more meaningful role in RFD potentiation than torque potentiation.

Apesar das perdas provocadas pela sarcopenia, o sistema neuromuscular do idoso ainda mantém parte da sua plasticidade. No entanto, as adaptações promovidas pelos treinamentos de força (TF) e de potência (TP) não foram totalmente elucidadas, assim como se existem diferenças entre essas adaptações nessa população. Para responder tais questões, 43 idosos (63,8 ± 4,0 anos; 67,2 ±13,4kg e 160,2 ±8,4cm), inexperientes em treinamento com pesos e independentes participaram desse estudo. Os voluntários foram distribuídos em três grupos: GF (n= 14; 70 a 90% de 1RM), GP (n= 16; 30 a 50% de 1RM) e GC (n= 13, não treinou). Durante 16 semanas o GF e o GP realizaram duas sessões de treino semanalmente. Os resultados significantes foram: aumento de 42,7% em GF e 33,8% em GP no teste de 1RM (leg press) e 31% em GF e 25,4% em GP (chest press); aumento de 6% em GF e 3,6% em GP na ASTq; aumento de 22,4% em GF e 17,1% em GP na CVIM e uma diminuição de 28% em GF e 32% em GP no REM. Não houve diferenças significativas entre GF e GP nas variáveis analisadas. Nenhum dos grupos apresentou aumento no sinal eletromiográfico nem na TDF. Não houve alteração significativa na funcionalidade. Portanto, ainda que com características distintas, o TF e o TP são similares em relação às adaptações analisadas, equiparando-se como estratégias de treinamento eficazes no combate à sarcopenia e seus efeitos / In spite of sarcopenia-induced losses, elderly peoples neuromuscular system keeps its plasticity. However, strength and power training-induced adaptations have not been completely elucidated. It also unknown if these adaptations are related to elderly functionality. Fourty three healthy and independent old men and women (63.8 ± 4.0 yrs; 67.2 ±13.4kg e 160.2 ±8.4cm) with no resistance training experience volunteered for this study. Participants were randomly distributed into three groups: GF (n= 14; 70 - 90%-1RM), GP (n= 16; 30 - 50%-1RM) e GC (n= 13, no training). GF and GP trained twice a week for 16 weeks. Leg-press (42.7% in GF and 33.8% in GP) and chest-press 1-RM (31% in GF and 25.4% in GP), quadriceps cross sectional area (6% in GF and 3.6% in GP), maximal voluntary isometric contraction (22.4% in GF and 17.1% in GP) were significantly increased in both groups. Electromechanical delay decreased 28% in GF and 32% in GP. There were no significant differences between groups. EMG and rate of force development did not change throughout the training period. Only main effect of time was observed for the functional tests. These results suggest that even with different characteristics, both strength and power training induce similar neuromuscular adaptations. Thus, both training regimens are equally effective in preventing and treating sarcopenia