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

Purpose: The purpose of our investigation was to compare repetition maximum (RM) to relative intensity using sets and repetitions (RISR) resistance training (RT) on measures of training load, vertical jump, and force production in well-trained lifters. Methods: Fifteen well-trained (isometric peak force= 4403.61+664.69 N, mean+SD) males underwent RT 3 d·wk-1 for 10-weeks in either an RM group (n=8) or RISR group (n=7). Weeks 8-10 consisted of a tapering period for both groups. The RM group achieved a relative maximum each day while the RISRgroup trained based on percentages. Testing at five time-points included unweighted ( Results: Moderate between-group effect sizes were observed for all SJ and CMJ conditions supporting the RISR group (g=0.76-1.07). A small between-group effect size supported RISR for allometrically-scaled isometric peak force (g=0.20). Large and moderate between-group effect sizes supported RISR for rate of force development from 0-50ms (g=1.25) and 0-100ms (g=0.89). Weekly volume load displacement was not different between groups (p>0.05), however training strain was statistically greater in the RM group (p<0.05). Conclusions: Overall, this study demonstrated that RISR training yielded greater improvements in vertical jump, rate of force development, and maximal strength compared to RM training, which may partly be explained by differences in the imposed training stress and the use of failure/non-failure training in a well-trained population.

Purpose: To assess the effects of manipulating the loading of successive sets of midthigh clean pulls on the potentiation capabilities of 7 international-level US weightlifters (4 men, 3 women). Methods: Isometric and dynamic peak-force characteristics were measured with a force plate at 500 Hz. Velocity during dynamic pulls was measured using 2 potentiometers that were suspended from the top of the right and left sides of the testing system and attached to both ends of the bar. Five dynamic-performance trials were used (in the following order) as the potentiation protocol: women at 60, 80, 100, 120, and 80 kg and men at 60, 140, 180, 220, and 140 kg. Trials 2 vs 5 were specifically analyzed to assess potentiation capabilities. Isometric midthigh pulls were assessed for peak force and rate of force development. Dynamic lifts were assessed for peak force (PF), peak velocity (PV), peak power (PP), and rate of force development (RFD). Results: Although all values (PF, PV, PP, and RFD) were higher postpotentiation, the only statistically higher value was found for PV (ICCα = .95, P = .011, η2 = .69). Conclusions: Results suggest that manipulating set-loading configuration can result in a potentiation effect when heavily loaded sets are followed by a lighter set. This potentiation effect was primarily characterized by an increase in the PV in elite weightlifters.

We determined whether aging diminishes bone blood flow and impairs endothelium‐dependent vasodilation. Femoral perfusion was lower in old animals, as well as endothelium‐dependent vasodilation and NO bioavailability. These effects could contribute to old age—related bone loss and the increased risk of fracture. Introduction: Aging has been shown to diminish bone blood flow in rats and humans. The purpose of this study was to determine whether blood flow to regions of the femur perfused primarily through the principal nutrient artery (PNA) are diminished with aging and whether this putative reduction in flow is associated with impaired endothelium‐dependent vasodilation. Materials and Methods: Blood flow was measured in conscious young adult (4–6 mo old) and aged (24–26 mo old) male Fischer‐344 rats using radiolabeled microspheres. Endothelium‐dependent vasodilation of the PNA was assessed in vitro using acetylcholine (ACh), whereas the contribution of the NO synthase (NOS) and cyclooxygenase (COX) signaling pathways to endothelium‐dependent vasodilation was determined using the NOS and COX inhibitors L‐NAME and indomethacin, respectively. Results: Femoral blood flow in the aged rats was 21% and 28% lower in the proximal and distal metaphyses, respectively, and 45% lower in the diaphyseal marrow. Endothelium‐dependent vasodilation was reduced with old age (young: 83 ± 6% maximal relaxation; aged: 62 ± 5% maximal relaxation), whereas endothelium‐independent vasodilation (sodium nitroprusside) was unaffected by age. The reduction in endothelium‐dependent vasodilation was mediated through impairment of the NOS signaling pathway, which resulted in lower NO bioavailability (young: 168 ± 56 nM; aged: 50 ± 7 nM). Conclusions: These data show that reductions in metaphyseal bone and diaphyseal marrow perfusion with old age are associated with diminished endothelium‐dependent vasodilation through an impairment of the NOS mechanism. Such age‐related changes in bone perfusion and vascular NO signaling could impact clinical bone loss, increase risk of fracture, and impair fracture healing in the elderly.

Recently, the comparison of “periodized” strength training methods has been a focus of both exercise and sport science. Daily undulating periodization (DUP), using daily alterations in repetitions, has been developed and touted as a superior method of training, while block forms of programming for periodization have been questioned. Therefore, the purpose of this study is to compare block to DUP in Division I track and field athletes. Thirty-one athletes were assigned to either a 10-wk block or DUP training group in which sex, year, and event were matched. Over the course of the study, there were 4 testing sessions, which were used to evaluate a variety of strength characteristics. Although performance trends favored the block group for strength and rate of force development, no statistically significant differences were found between the 2 training groups. However, statistically different (P ≤ .05) values were found for estimated volume of work (volume load) and the amount of improvement per volume load between block and DUP groups. Based on calculated training efficiency scores, these data indicate that a block training model is more efficient than a DUP model in producing strength gains.

Currently, whole-body vibration is being used to promote enhanced performance. Many coaches and athletes believe that it can acutely enhance explosive performance and power output. However, the scientific literature is unclear as to whether this enhancement occurs. The purpose of this study was to examine the acute effects of whole-body vibration on static jump performance, including jump height, peak force, rate of force development, and peak power. Fourteen recreationally active individuals (5 females, 9 males) participated in three separate randomized treatment sessions. Treatment 1 consisted of no vibration while treatment 2 and treatment 3 incorporated whole-body vibration. The whole-body vibration protocol consisted of three 30-s bouts of vibration performed at 30 Hz and low amplitude ( 3 mm) with a 30-s rest between bouts. Treatment 1 was identical in duration to both treatments 2 and 3, but did not contain any vibration. Five minutes after each treatment, the participants performed the static jump protocols. Two (data averaged) non-weighted static jumps and two 20 kg weighted jumps were performed. Treatments 1 vs. 2, 1 vs. 3, and 2 vs. 3 were calculated for each variable at both 0 kg and 20 kg. Jump height, peak force, rate of force development, and peak power were analysed using a one-way analysis of variance with repeated measures. The intra-class correlations comparing the two trials of each jump for each of the three treatments were ≥0.92. Compared with the no-vibration condition, jump height showed a non-significant increase as a result of whole-body vibration for both unweighted and weighted jumps; peak force, rate of force development, and peak power were not statistically different. The results indicate that whole-body vibration has no effect on jump height, peak force, rate of force development or peak power during static jumping.