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Cosic, M, Knezevic, OM, Nedeljkovic, A, Djuric, S, Zivkovic, MZ, and Garcia-Ramos, A. Effect of different types of loads on the force-velocity relationship obtained during the bench press throw exercise. J Strength Cond Res 35(9): 2401-2406, 2021-This study aimed (a) to evaluate the degree of linearity of the force-velocity (F-V) relationship across different types of loads, (b) to compare the magnitude of the F-V relationship parameters (maximum values of force [F0], velocity [V0], and power [Pmax]) between the different types of loads, and (c) to explore the concurrent validity of F0 with traditional measures of maximal strength. The F-V relationships of 15 physically active men (age: 20.9 ± 2.0 years, bench press 1 repetition maximum relative to body mass: 1.20 ± 0.10 kg·kg-1) were determined during the bench press throw exercise using predominantly gravitational (W), inertial (I), and combined (W + I) loads. The bench press maximal isometric force (Fiso) and the 1RM were also assessed. The individual F-V relationships were highly linear regardless of the type of load considered (median r [range] = 0.98 [0.94, 1.00]). The W + I load provided the largest value of F0 (972 ± 45 N; 6.0 and 14.6% higher than W and I, respectively), the I load the largest value of V0 (2.99 ± 0.34 m·s-1; 40.4 and 20.1% higher than W and W + I, respectively), and the W load the lowest value of Pmax (501 ± 46 W; -22.7 and -17.1% lower than I and W + I, respectively). The F0 obtained from the W load presented the highest association with Fiso and 1RM values (r0.90). The W + I load and the I load should be recommended to work closer to the F0 and V0 capacities, respectively. However, the W load should be recommended to assess maximal strength capacity through the value of F0.

The aim of this study was to investigate the resistance-specific gains in muscle power and strength (1RM) following the training of maximum bench-press throws (BPT) against constant, inertial, and combined resistance. Forty-eight male participants (age 20.5 ± 2.0 years) were randomly assigned to the constant, inertial, combined resistance, or control group. Participants underwent 8 weeks of training of BPT against the loads that corresponded to the different effects of mass of 40 kg (∼50% of 1RM). The gains in average and maximum power, and 1RM were significant in all experimental groups (P < 0.01), but not in the control group (P > 0.1). Relative gains in the average (26.3 ± 9.8%) and maximum power (25.2 ± 9.8%) were larger than that in the 1RM (mean 7.2 ± 6.9%; both P < 0.001). The gains in the average (F4, 66 = 6.0; P < 0.01) and maximum power (F4, 66 = 4.7; P < 0.01) were higher when tested against the training-specific resistance than when tested against the remaining two resistance types. Differences in 1RM among experimental groups were not significant (P = 0.092). The most important and rather novel finding of the study is that the training against the weight and inertial resistance, and their combination results in resistance-specific gains in muscle power, although the overall gains muscle strength and power remain comparable across the training protocols.

This study aimed to explore the effect of the knee angle and loading condition on the magnitude and reliability of squat jump (SJ) performance variables. Thirteen male sport sciences students performed in a random order 4 SJ types (knee angle of 80o [SJ80], 90o [SJ90], 100o [SJ100], and self-preferred [SJ(pref)]) against 3 external loads. The push-off distance (HpO), jump height (Hmax), maximum force (Fmax) and maximum power (Pmax) were obtained from force platform recordings. The HpO during the SJ(pref) (43.4 +/- 6.4 cm) was always between SJ90 (44.3 +/- 4.8 cm) and SJ100 (40.5 +/- 4.2 cm). The magnitudes of Hmax, Fmax and Pmax were comparable or higher during the SJ(pref). The increase of the knee angle was associated with larger values of Fmax and Pmax, but no significant differences were observed for Hmax. An acceptable reliability was observed for HpO (coefficient of variation [CV] lt = 5.09% and intraclass correlation coefficient [ICC] gt = 0.78), Hmax (CV lt = 6.06% and ICC gt = 0.84), Fmax (CV lt = 3.25% and ICC gt = 0.96) and Pmax (CV lt = 2.93% and ICC gt = 0.96). Reliability did not systematically differ between the 4 SJ types. In conclusion, the higher magnitudes and comparable reliability of the performance variables obtained during the SJ(pref) support its use for testing lower-body ballistic performance against different loads.

This research was funded by the Slovenian Research Agency under Grants L5-1845, P5-0147, and BI-RS/18-19-010; Ministry of Education, Science and Technological Development of Republic of Serbia under Grants 451-03-68/2020-14/200015 and 451-03-68/2020-14/200021. The experiments comply with the current laws of the country in which they were performed. The authors have no conflict of interest to declare. The datasets generated during and/or analyzed during the current study are not publicly available, but are available from the corresponding author who was an organizer of the study., This study aimed to assess the within- and between-session reliability of the KiSprint system for determining force-velocity-power (FVP) profiling during sprint running. Thirty (23 males, 7 females; 18.7 +/- 2.6 years;) young high-level sprinters performed maximal effort sprints in two sessions separated by one week. Split times (5, 10, 20 and 30 m), which were recorded with a laser distance meter (a component of the KiSprint system), were used to determine the horizontal FVP profile using the Samozino's field-based method. This method assesses the FVP relationships through estimates of the step-averaged ground reaction forces in sagittal plane during sprint acceleration using only anthropometric and spatiotemporal (split times) data. We also calculated the maximal theoretical power, force and velocity capabilities and the slope of the FV relationship, the maximal ratio of horizontal-to-resultant force (RF), and the decrease in the RF (D-RF). Overall, the results showed moderate or good to excellent within- and between-session reliability for all variables (ICC > 0.75; CV < 10 %), with the exception of FV slope and D-RF that showed low relative reliability (ICC = 0.47-0.48 within session, 0.31-0.33 between-session) and unacceptable between-session absolute reliability values (CV = 10.9-11.1 %). Future studies are needed to optimize the protocol in order to maximize the reliability of the FVP variables, especially when practitioners are interested in the FV slope and D-RF. In summary, our results question the utility of the sprint-based FVP profiling for individualized training prescription, since the reliability of the FV slope and D RF variables is highly questionable., Slovenian Research Agency - Slovenia L5-1845 P5-0147 BI-RS/18-19-010, Ministry of Education, Science and Technological Development of Republic of Serbia 451-03-68/2020-14/200015 451-03-68/2020-14/200021

Purpose: To test whether the force–velocity (F–V) relationship obtained during a specific single-stroke kayak test (SSKT) and during nonspecific traditional resistance-training exercises (bench press and prone bench pull) could discriminate between 200-m specialists and longer-distance (500- and 1000-m) specialists in canoe sprint. Methods: A total of 21 experienced male kayakers (seven 200-m specialists and 14 longer-distance specialists) participated in this study. After a familiarization session, kayakers came to the laboratory on 2 occasions separated by 48 to 96 hours. In a randomized order, kayakers performed the SSKT in one session and the bench press and bench pull tests in another session. Force and velocity outputs were recorded against 5 loads in each exercise to determine the F–V relationship and related parameters (maximum force, maximum velocity, F–V slope, and maximum power). Results: The individual F–V relationships were highly linear for the SSKT (r = .990 [.908, .998]), bench press (r = .993 [.974, .999]), and prone bench pull (r = .998 [.992, 1.000]). The F–V relationship parameters (maximum force, maximum velocity, and maximum power) were significantly higher for 200-m specialists compared with longer-distance specialists (all Ps ≤ .047) with large effect sizes (≥0.94) revealing important practical differences. However, no significant differences were observed between 200-m specialists and longer-distance specialists in the F–V slope (P ≥ .477). Conclusions: The F–V relationship assessed during both specific (SSKT) and nonspecific upper-body tasks (bench press and bench pull) may distinguish between kayakers specialized in different distances.

Rate of force/torque development scaling factor (RFD-SF/RTD-SF) was recently introduced as a tool to quantify the neuromuscular quickness, and it could have potential for interlimb asymmetry identification. Moreover, positive relationships in RFD-SF ability among different muscle groups were shown, but not in the lower extremity. The first aim of our study was to use RTD-SF for interlimb asymmetry identification. The second aim was to determine associations between plantar flexors (PF) and knee extensors (KE). Forty young healthy athletes (14.8 ± 1.2 years) performed explosive isometric contractions to a span of torque levels for PF and KE. From rapid isometric contractions, the RTD-SF and linearity (r2) of the regression line were calculated. Using RTD-SF we identified 10% (PF) and 15% (KE) of subjects with contralateral asymmetries (>15% criterion). The results revealed significant positive moderate correlation in RTD-SF between PF and KE (r = 0.401,p< 0.05). We supported that RTD-SF can be a useful tool for interlimb asymmetry identification. Future research about observed asymmetry in rapid submaximal contractions deserves more attention, as most of the functional sport specific activities put high demands on rapid force production. Our study as first confirmed positive associations in RTD-SF ability between muscle groups in lower limbs.

This study aimed to compare the magnitude of the force-velocity (F-V) relationship parameters (maximum force [F-0], maximum velocity [V-0], F-V slope, and maximum power [P-max]) between the squat jumps (SJ) performed from different knee angles. The F-V relationships of 12 men were assessed in 3 sessions during the SJ performed from a knee angle of 80 degrees (SJ80), 90 degrees (SJ90) and 100 degrees (SJ100). The SJ100 provided likely to very likely higher values of F-0 and P-max compared to SJ80 (86% and 98%, respectively) and SJ90 (73% and 94%, respectively), while unclear and trivial differences were observed for the remaining comparisons. The magnitude of the correlations between the 3 SJ types was very large to nearly perfect for P-max (r range = 0.864 to 0.940), moderate to very large for F-0 (r range = 0.438 to 0.778), and small to large for V-0 (r range = 0.361 to 0.642) and the F-V slope (r range = 0.178 to 0.645). These results suggest that the F-V relationship assessed during the SJ exercise is affected by the initial knee angle with the increase of the knee angle from 80 degrees to 100 degrees being associated with higher values of F-0 and P-max, while V-0 remains unchanged.

(1) Background: Within the current study we aimed at exploring gender-related differences and the relationship between sprint start block kinematics and kinetics and sprint acceleration force&ndash, velocity (F-v) relationship parameters (maximal force [F0], maximal velocity [v0], maximal power [Pmax] and slope) in top national-level sprinters. (2) Methods: Twenty-eight sprinters (6 females) performed 10 maximal 30-m sprints. Start block and acceleration kinematics and kinetics were collected with an instrumented sprint start block and a laser distance sensor (KiSprint system). Displacement-time data were used to determine the F-v relationship through Samozino&rsquo, s method. (3) Results: Start block rear foot maximal force (effect size [ES] = 1.08), rate of force development (ES = 0.90&ndash, 1.33), F0 (ES = 1.38), v0 (ES = 1.83) and Pmax (ES = 1.95) were higher in males than in females (p &le, 0.05). There were no differences in the slope, and ratio of horizontal-to-resultant force. F0, v0, and Pmax generally presented higher correlations with the start block kinetics (median r [range] = 0.49 [0.28, 0.78]) than with the kinematics (median r [range] = &minus, 0.27 [&minus, 0.52, 0.28]). (4) Conclusions: We confirmed that sprint block phase and sprint acceleration mechanics should be mutually assessed when analyzing sprinting performance. KiSprint system could provide more accurate information regarding mechanical pattern and technique during sprint initiation and acceleration, and potentially help create a more personalized and effective training program.

Background: Isokinetic testing has been routinely used to assess the capacities of individual muscle groups. In this study we aimed to evaluate the sensitivity of the force-point (F-v) relationship assessed through the two-point method to discriminate between antagonist muscle groups and males with di erent physical activity levels. Methods: The concentric force output of the knee, hip, elbow, and shoulder flexors and extensors of 27 active and 13 non-active men was recorded at 60 and 180 /s to determine the F-v relationship parameters (maximum force [F0], maximum velocity [v0], and maximum power [Pmax]). Results: F0 and Pmax were higher for knee extensors (e ect size [ES] = 1.97 and 0.57, respectively), hip extensors (ES = 2.52 and 0.77, respectively), and shoulder flexors (ES = 1.67 and 0.83, respectively) compared to their antagonist muscles, while v0 was higher for knee flexors compared to knee extensors (ES = 0.59). Active males revealed higher F0 for knee extensors (ES = 0.72) and knee flexors (ES = 0.83) and higher Pmax for knee flexors (ES = 0.70), elbow extensors (ES = 0.83) and shoulder extensors (ES = 0.36). Conclusions: The sensitivity of the two-point method for testing the maximal mechanical capacities was high for the knee, moderate for the hip and shoulder, and low for the elbow joint., Ministry of Education, Science, and Technological Development of the Republic of Serbia 451-03-68/2020-14/200015 451-03-68/2020-14/200021

This study aimed to compare the reliability and magnitude of the force-velocity (F-V) relationship parameters between the squat jumps performed from the 90 degrees (SJ90) and self-preferred knee angle (SJ(pref)). A secondary aim was to explore the effect of the analysis procedure (force platform [FP] and Samozino's [SAM] method) and the number of loads tested (three- and two-point methods) on the F-V relationships. Twelve men were tested in two sessions during the SJ90 and SJ(pref). Two identical blocks of jumps were performed in each session against three external loads. The F-V relationship parameters (maximum force, maximum velocity, F-V slope and maximum power) were determined at each block through the FP and SAM procedures using the data collected under three (three-point method) or only the two most distant loads (two-point method). The average coefficient of variation (CV) of the four F-V parameters revealed a higher reliability for the SJ90 compared to the SJ(pref) (5.86% vs. 7.55%; CVratio = 1.29) with more pronounced differences using the FP (CVratio = 1.43) than the SAM procedure (CVratio = 1.14), and higher reliability for the SAM compared to the FP (6.14% vs. 7.27%; CVratio = 1.18). The SJ(pref) and SAM procedures provided comparable or higher magnitude of the F-V relationship parameters than the SJ90 and FP, respectively. The three- and two-point methods revealed a comparable reliability and trivial differences in the magnitude of the F-V relationship parameters. The routine testing procedure of the F-V relationship could be simplified using the SJ(pref), the SAM procedure and the two-point method. This is the peer-reviewed version of the article: Janićijević, D.; Knežević, O.; Mirkov, D. M.; Perez-Castilla, A.; Petrović, M. R.; Samozino, P.; Garcia-Ramos, A. Assessment of the Force-Velocity Relationship during Vertical Jumps: Influence of the Starting Position, Analysis Procedures and Number of Loads. European Journal of Sport Science 2020, 20 (5), 614–623. [https://doi.org/10.1080/17461391.2019.1645886]

The aim of the study was to compare the effects of high-intensity interval training (HIIT) and nutrition advice on cardiometabolic biomarkers, hormonal parameters, and cardiorespiratory fitness in adolescent girls with obesity. Adolescent girls with obesity (n = 44, aged 13–19 years) were randomized into a 12-week intervention as follows: (i) dietary advice and HIIT (n = 22), and (ii) dietary advice only (n = 22). The concentration of biomarkers of inflammation, biochemical and hormonal testing, oral glucose tolerance test, cardiorespiratory fitness, physical activity levels, and nutrition were assessed. After a 3-month intervention, the diet+HIIT group significantly increased insulin sensitivity index (–0.34 ± 1.52 vs. 1.05 ± 3.21; p = 0.001) and work load (0.6 ± 11.3 W vs. 14.6 ± 20.2 W; p = 0.024) and decreased glucose area under the curve (–0.29 ± 4.69 vs. −0.98 ± 4.06; p = 0.040), insulin area under the curve (−9.65 ± 117.9 vs. −98.7 ± 201.8; p = 0.003), and high-sensitivity C-reactive protein (hs-CRP) (0.12 ± 1.92 mg/L vs. −1.47 ± 3.67 mg/L; p = 0.039) in comparison with the diet group. Regarding within-group changes, both groups had significant improvements in body mass index (BMI), BMI-standard deviation score, body fat percentage, and systolic blood pressure. Positive impact on waist circumference, waist circumference/height ratio, diastolic blood pressure, hs-CRP, work load, maximal heart rate, and resting heart rate was observed only after the diet+HIIT intervention. No significant change was noted in peak oxygen uptake, lipid profile, and hormonal parameters between groups after intervention. Novelty HIIT and nutrition advice increased insulin sensitivity and decreased BMI, body fat, systolic blood pressure, and diastolic blood pressure. Nutrition advice decreased BMI, body fat, and systolic blood pressure in adolescent girls with obesity.

This study aimed to (1) evaluate the shape of the force-velocity (F-V) relationship obtained from different muscles, (2) explore the concurrent validity of the two-point method with respect to the multiple-point method, (3) evaluate whether the F-V relationship can discriminate between muscle groups and genders, and (4) explore the generalisability of the same F-V relationship parameters (maximal force [F-0], maximal velocity [V-0]), and maximal power [P-0]) between different tasks. The F-V relationship of 22 physically active participants (12 women) were tested during knee extension, knee flexion, elbow extension and elbow flexion through the multiple- (eight velocities: 30-60-90-120-150-180-210-240o/s) and two-point (two velocities: 60-180o/s) methods. The findings revealed (1) highly linear F-V relationships (r gt = 0.893), (2) high concurrent validity of the two-point method for F-0, but lower for V-0 and P-0, (3) the outcomes of both methods were sensitive to the muscle groups (higher for knee muscles) and gender (higher for men), and (4) the magnitude of the same F-V parameters were poorly correlated between different tasks (median r lt 0.1). These results support the two-point method as a valid and sensitive procedure for determining the maximal capacities of the muscles to produce F, but not V, during isokinetic tests.

Petronijevic, MS, Garcia Ramos, A, Mirkov, DM, Jaric, S, Valdevit, Z, and Knezevic, OM. Self-preferred initial position could be a viable alternative to the standard squat jump testing procedure. J Strength Cond Res 32(11): 3267-3275, 2018-The purpose of this study was to compare both the magnitude and reliability of different variables (knee angle, squat depth, jump height [Hmax], maximum force [Fmax], and maximum power [Pmax]) between the standardized squat jump (SJ) and the SJ performed from the self-preferred position. Eleven team handball players (age: 19.5 ± 1.1 years; height: 1.88 ± 0.06 m; and body mass: 82.1 ± 8.7 kg) and 13 physically active students (age: 20.5 ± 0.9 years; height: 1.81 ± 0.06 m; and body mass: 76.6 ± 6.6 kg) were evaluated on 2 sessions during the standardized SJ (knee angle fixed at 90°) and the self-preferred SJ (self-selected knee angle to maximize Hmax). Two blocks of both 3 standardized SJ and 3 self-preferred SJ were performed on the first session, whereas only 1 block was performed in the second session. The squat depth was smaller for the self-preferred SJ, whereas the knee angle, Fmax, and Pmax were higher for the self-preferred SJ (p < 0.025). The magnitude of Hmax did not significantly differ between both jump types. Most importantly, the reliability of the mechanical outputs (Hmax, Fmax, and Pmax) was generally higher for the self-preferred SJ (9 of 12 comparisons), whereas only in 2 of 12 comparisons the reliability was meaningfully higher for the standardized SJ. No differences were observed between presumably more (handball players) and less skilled individuals (physically active subjects). These results suggest that the self-preferred SJ should be recommended over the standardized SJ (90° knee angle) because it is not only quicker and more ecologically valid, but could also provide the performance variables with higher reliability.

The aim of this study was to assess the effect of a unilateral anterior cruciate ligament reconstruction (ACLR) on maximum voluntary contraction (MVC) and explosive strength of both the involved limb and the uninvolved limb. Nineteen male athletes completed a standard isometric testing protocol 4months post-ACLR, while 16 healthy participants served as a control group (CG). The explosive strength of the knee extensors and flexors was assessed as RFD obtained from the slope of the force-time curves over various time intervals. Both muscle groups of the involved limb had significantly lower MVC compared to the uninvolved. The involved limb also had significantly lower RFD in the late phase of contraction (140-250ms) for both knee extensors and flexors (P lt 0.05). There was no difference in MVC between the uninvolved limb and the CG. However, RFD of the uninvolved limb was lower compared to CG for both knee extensors (0-180ms; P lt 0.01) and flexors (0-150ms; P lt 0.05). ACLR leads to lower MVC and explosive strength of the involved limb. As a consequence of potential crossover (presumably neural-mediated) effects, explosive strength deficits could be bilateral, particularly in the early phase of the contraction ( lt 100ms).

Single outcomes of standard isokinetic dynamometry tests do not discern between various muscle mechanical capacities. In this study, we aimed to (1) evaluate the shape and strength of the force-velocity relationship of knee extensors, as observed in isokinetic tests conducted at a wide range of angular velocities, and (2) explore the concurrent validity of a simple 2-velocity method. Thirteen physically active females were tested for both the peak and averaged knee extensor concentric force exerted at the angular velocities of 30°–240°/s recorded in the 90°–170° range of knee extension. The results revealed strong (0.960

To investigate the selective effects of different types of external loads applied in vertical jump training on both the performance and muscle power output of the squat (SJ) and countermovement jump (CMJ). Physically active males practiced maximum unconstrained vertical jumps over an 8-week period with no load, with either a negative or positive load exerted by a nearly constant external force that altered their body weight, and with a loaded vest that increased both the body weight and inertia. The magnitude of all applied loads corresponded to 30 % of body weight. A similar training-associated increase in jump height was observed in all experimental groups in both CMJ (7.4-11.8 %) and SJ (6.4-14.1 %). The relative increase in power output was comparable to the increase in jump height in SJ (7.4-11.5 %), while the power increase in CMJ was relatively small and load-specific (0.5-9.5 %). The observed differences could originate from the changes in the CMJ pattern, reflected through the depth of the counter movement that particularly increased after the training with negative load (42 %) and no load (21 %). The same participants also revealed increased CMJ duration, reduced ground reaction forces, as well as reduced maximum and average power output when compared with other training groups. Jump training with the applied loads could lead to a comparable improvement in jumping performance. However, the observed load-specific adaptations of CMJ pattern could decouple the training-associated increase in jump height from the increase in muscle power output.

Low back pain (LBP) is nowadays one of the most widely experienced health-related problems. First symptoms usually appear between the age of thirty and fifty, although it has been recorded in athletes in early twenties . Etiology of LBP is multifactorial and it is thought that non-specific LBP is associated with lumbar spine instability 4, . It is generally believed that spinal instability (such as in circumstances with no neurological deficit, deformity, or the presence of pain) is associated with reduced capabilities of neuromuscular system to respond to physiological loadings . The spine is a mechanically complex structure which is inherently unstable. Due to the redundancy in the neuromuscular and spinal system, there is a large set of possible muscle activation patterns to meet the stability constraints . However, different muscle activation patterns can significantly affect the magnitude and direction of the intervertebral loadings and, therefore, the spinal and core stability. Muscle activation patterns when either retaining different postures or performing various movements and their relationship with LBP is of much interest for researchers and the clinical practice. Theoretically, the unbalanced activation and coactivation may lead to a mechanical imbalance of the whole body system 4, . However, there is a disagreement among the researchers to what extent the changes in trunk muscles activation level and recruitment patterns contribute to the presence of pain (and later on to its reduction) and the altered core stability . However, research in the area of motor control has made a significant contribution to understanding of the neuromuscular reorganization due to LBP. Core stability and the role of deep trunk muscles

The aim of the present study was to explore the control strategy of maximum countermovement jumps regarding the preferred countermovement depth preceding the concentric jump phase. Elite basketball players and physically active non-athletes were tested on the jumps performed with and without an arm swing, while the countermovement depth was varied within the interval of almost 30 cm around its preferred value. The results consistently revealed 5.1-11.2 cm smaller countermovement depth than the optimum one, but the same difference was more prominent in non-athletes. In addition, although the same differences revealed a marked effect on the recorded force and power output, they reduced jump height for only 0.1-1.2 cm. Therefore, the studied control strategy may not be based solely on the countermovement depth that maximizes jump height. In addition, the comparison of the two groups does not support the concept of a dual-task strategy based on the trade-off between maximizing jump height and minimizing the jumping quickness that should be more prominent in the athletes that routinely need to jump quickly. Further research could explore whether the observed phenomenon is based on other optimization principles, such as the minimization of effort and energy expenditure. Nevertheless, future routine testing procedures should take into account that the control strategy of maximum countermovement jumps is not fully based on maximizing the jump height, while the countermovement depth markedly confound the relationship between the jump height and the assessed force and power output of leg muscles.

Introduction Maximal strength ratios such as the limb symmetry index (LSI) and hamstring-to-quadriceps ratio (HQ) may be considered the main outcome measures in the monitoring of recovery after anterior cruciate ligament (ACL) reconstruction. Although explosive strength is much more important than maximal strength, it is generally disregarded in the follow-up of muscle function recovery. Objective The purpose of this study was to compare ratios between maximal (Fmax) and explosive strength (rate of force development - RFD) in individuals with ACL reconstruction. Methods Fifteen male athletes were enrolled and had maximum voluntary isometric quadriceps and hamstring contractions tested (4.0 ± 0.1 months post reconstruction). In addition to Fmax, RFD was estimated (RFDmax as well as RFD at 50, 100, and 200 ms from onset of contraction) and LS gt I and HQ ratios were calculated. Results The involved leg demonstrated significant hamstring and quadriceps deficits compared to uninvolved leg (p lt 0.01). Deficits were particularly significant in the involved quadriceps, causing higher HQ ratios (average 0.63), compared to the uninvolved leg (0.44). LSI was significantly lower for RFD variables (average 55%) than for Fmax (66%). Conclusion The assessment of RFD may be considered an objective recovery parameter for one's readiness to return to sports and should be an integral part of standard follow-up protocol for athletes after ACL reconstruction. Moreover, the combination of indices derived from maximal and explosive strength may provide better insight in muscle strength balance, as well as a clear picture of functional implications. Uvod Maksimalne jačine ekstenzora i fleksora kolena, njihov međusobni odnos (eng. hamstrings-to-quadriceps ratio; HQ), kao i indeks simetrije operisane i neoperisane noge (eng. limb symmetry index; LSI) važni su pokazatelji pomoću kojih se prati oporavak nakon rekonstrukcije LCA. Iako je za izvođenje brojnih funkcionalnih zadataka eksplozivna jačina važnija od maksimalne, ova sposobnost generalno je zanemarena u praćenju oporavka mišićne funkcije. Cilj rada bio je da se uporede odnosi (maksimalne jačine (Fmax) i odnosi eksplozivne jačine (eng. Rate of Force Development - RFD) kod sportista sa rekonstrukcijom LCA. Metode rada U studiju je uključeno 15 sportista, kojima je testirana maksimalna voljna izometrijska kontrakcija (MBK) ekstenzora i fleksora kolena (4,0 ± 0,1 meseca postoperativno). Pored Fmax, procenjivan je i RFD (RFDmax, kao i RFD na 50, 100 i 200 ms od početka kontrakcije) i računati odnosi jačine (LSI i HQ odnos). Rezultati Maksimalna jačina i ekstenzora i fleksora operisane noge bila je značajno niža nego kod neoperisane noge (p lt 0,01). Deficiti su bili posebno izraženi kod ekstenzora operisane noge, usled čega su i HQ odnosi na toj strani (prosečno 0,63) bili veći nego kod neoperisane noge (0,44). Indeks simetrije je bio značajno niži za varijable RFD (prosečno 55%) nego za Fmax (66%). Zaključak Procena eksplozivne jačine može biti još jedan objektivni pokazatelj oporavka i spremnosti za izlaganje specifičnim opterećenjima i kretnjama, zbor čega bi trebalo da bude deo standardnog protokola za praćenje sportista nakon rekonstpukcije LCA. Štaviše, kombinacija indeksa izvedenih iz maksimalne i eksplozivne jačine morala bi dati kompletniji uvid u balans jačine mišića za kretnje koje zahtevaju maksimalne i eksplozivne akcije, kao i jasnu sliku o funkcionalnim implikacijama.

Prominent endosomal and lysosomal changes are an invariant feature of neurons in sporadic Alzheimer's disease (AD). These changes include increased levels of lysosomal hydrolases in early endosomes and increased expression of the cation-dependent mannose 6-phosphate receptor (CD-MPR), which is partially localized to early endosomes. To determine whether AD-associated redistribution of lysosomal hydrolases resulting from changes in CD-MPR expression affects amyloid precursor protein (APP) processing, we stably transfected APP-overexpressing murine L cells with human CD-MPR. As controls for these cells, we also expressed CD-MPR trafficking mutants that either localize to the plasma membrane (CD-MPRpm) or to early endosomes (CD-MPRendo). Expression of CD-MPR resulted in a partial redistribution of a representative lysosomal hydrolase, cathepsin D, to early endosomal compartments. Turnover of APP and secretion of sAPPalpha and sAPPbeta were not altered by overexpression of any of the CD-MPR constructs. However, secretion of both human Abeta40 and Abeta42 into the growth media nearly tripled in CD-MPR- and CD-MPRendo-expressing cells when compared with parental or CD-MPRpm-expressing cells. Comparable increases were confirmed for endogenous mouse Abeta40 in L cells expressing these CD-MPR constructs but not overexpressing human APP. These data suggest that redistribution of lysosomal hydrolases to early endocytic compartments mediated by increased expression of the CD-MPR may represent a potentially pathogenic mechanism for accelerating Abeta generation in sporadic AD, where the mechanism of amyloidogenesis is unknown.

Background: Despite its apparent functional importance, there is a general lack of data regarding the time-related changes in explosive strength and the corresponding side-to-side asymmetries in individuals recovering from an ACL reconstruction (ACLR). The present study was designed to assess changes in the maximum and explosive strength of the quadriceps and hamstring muscles in athletes recovering from an ACLR. Methods: Twenty male athletes with an ACL injury completed a standard isometric testing protocol pre-ACLR, four and six months post-ACLR. In addition to the maximum strength (F-max), the explosive strength of quadriceps and hamstrings was assessed through four variables derived from the slope of the force-time curves over various time intervals (REDmax, RED50, RFD150 and RED250). Side-to-side asymmetries were calculated relative to post-ACLR measures of the uninvolved leg ("standard" asymmetries), and relative to pre-ACLR value of the uninvolved leg ("real" asymmetries). Results: Pre-ACLR asymmetries in quadriceps RFD (average 26%) were already larger than in F-max (14%) (p lt 0.05). Six months post-ACLR real asymmetries in RFD variables (33-39%) were larger than the corresponding standard asymmetries (26-28%; p lt 0.01). Average asymmetries in hamstrings' RFD and F-max were 10%, 25% and 15% for pre-ACLR and two post-ACLR sessions, respectively (all p gt 0.05). Conclusions: In addition to the maximum strength, the indices of explosive strength should also be included in monitoring recovery of muscle function following an ACLR. Furthermore, pre-injury/reconstruction values should be used for the post-ACLR side-to-side comparisons, providing a more valid criterion regarding the muscle recovery and readiness for a return to sports.

The novel test based on isometric alternating consecutive maximal contractions performed by two antagonistic muscles has been recently proposed as a test of muscle function in healthy subjects. The aim of this study was to evaluate reliability and sensitivity of a novel test as a test of knee muscles function in athletes recovering from anterior cruciate ligament reconstruction. Fifteen male athletes with recent ligament reconstruction (4.0 ± 0.1 months following the surgery) and 15 sport and physical education students participated in the study. Peak torques of the quadriceps and hamstring muscles assessed both through the alternating consecutive maximal contractions and standard isokinetic test performed at 60 º/s and 180 º/s served for calculation of the hamstrings-to-quadriceps ratio and the bilateral difference in strength. When applied on individuals recovering from anterior cruciate ligament reconstruction, the novel test revealed a high within-day reliability and sensitivity for detecting imbalances both between antagonistic and between contralateral muscles. The present findings suggest that alternating consecutive maximal contractions could be used as a test of muscle function that is either complementary or alternative to the isokinetic test, particularly in the laboratories where the isokinetic devices are not available. Potential advantages of the novel test could be both a brief testing procedure and a possibility to conduct it using relatively inexpensive devices such as custom made kits containing a single one-axis force transducer.