Poor correlations between isometric tests and dynamic performance: relationship to muscle activation

Comparison of Supervised versus Self-Administered Stretching on Bench Press Maximal Strength and Force Development

PURPOSE

While there is reported superior effectiveness with supervised training, it usually requires specialized exercise facilities and instructors. It is reported in the literature that high-volume stretching improves pectoralis muscles strength under supervised conditions while practical relevance is discussed. Therefore, the study objective was to compare the effects of volume equated, supervised- and self-administered home-based stretching on strength performance.

METHODS

Sixty-three recreational participants were equally assigned to either a supervised static stretching, home-based stretching, or control group. The effects of 15 min pectoralis stretching, 4 days per week for 8 weeks, were assessed on dynamic and isometric bench press strength and force development.

RESULTS

While there was a large magnitude maximal strength increase (p < 0.001-0.023, ƞ2 = 0.118-0.351), force development remained unaffected. Dynamic maximal strength in both groups demonstrated large magnitude increases compared to the control group (p < 0.001-0.001, d = 1.227-0.905). No differences between the intervention group for maximal strength (p = 0.518-0.821, d = 0.101-0.322) could be detected.

CONCLUSIONS

The results could potentially be attributed to stretch-induced tension (mechanical overload) with subsequent anabolic adaptations, and alternative explanatory approaches are discussed. Nevertheless, home-based stretching seems a practical alternative to supervised training with potential meaningful applications in different settings.

The Impact of Range of Motion on Applied Force Characteristics and Electromyographic Activity during Repeated Sets of Bench Press Exercise

This study examined the effects of range of motion (ROM) on applied force, power output and surface electromyographic (sEMG) responses during repeated sets of bench press exercise executed as fast as possible. Ten resistance trained men performed three sets to momentary failure with two-min rest intervals under three different ROM conditions: (a) full ROM (FULL), (b) TOP, at the top half of ROM, and (c) BOTTOM, at the bottom half of ROM. Mean and peak force were higher in TOP compared to FULL and BOTTOM (mean force: 817 ± 80 vs. 657 ± 98 vs. 623 ± 122 N, respectively, p < 0.001) with no differences between FULL and BOTTOM. During repeated sets, large decreases were found in peak (by 29.4 to 45.3%) and mean power (by 55.5 to 64.7%) from the first to the last repetitions. However, the decrease in mean force was only 2% (p < 0.01) and decreases in peak force ranged from 6.7 and 8.8% to zero, indicating the velocity loss was the main contributor to fatigue in power output. Although force and power output in set 3 were unchanged in BOTTOM, mean power output decreased significantly, suggesting that lower performance and fatigue may be related to the longer muscle length. Fatigue was accompanied by an increase in sEMG activity and a decrease in median frequency in all muscles, with triceps brachialis sEMG reflecting more the force and power differences among ROMs. In conclusion, fatigue depends on velocity rather than force loss during bench press exercise at different ROMs.

Fatigue and Metabolic Responses during Repeated Sets of Bench Press Exercise to Exhaustion at Different Ranges of Motion

This study compared the acute effects of different ranges of motion (ROM) on fatigue and metabolic responses during repeated sets of bench press exercise. Ten resistance trained men performed three sets to momentary failure with two-min rest intervals at three different ROM: full ROM (FULL), and partial ROM in which the barbell was moved either at the bottom half (BOTTOM) or the top half (TOP) of the full barbell vertical displacement. In TOP, a higher load was lifted, and a higher total number of repetitions was performed compared to FULL and BOTTOM (130 ± 17.6 vs. 102.5 ± 15.9 vs. 98.8 ± 17.5 kg; 55.2 ± 9.8, 32.2 ± 6.5 vs. 49.1 ± 16.5 kg, respectively p < 0.01). Work per repetition was higher in FULL than TOP and BOTTOM (283 ± 43 vs. 205 ± 32 vs. 164 ± 31 J/repetition, p < 0.01). Mean barbell velocity at the start of set 1 was 21.7% and 12.8% higher in FULL compared to TOP and BOTTOM, respectively. The rate of decline in mean barbell velocity was doubled from set 1 to set 3 (p < 0.01) and was higher in FULL than both TOP and BOTTOM (p < 0.001). Also, the rate of mean barbell velocity decline was higher in BOTTOM compared to TOP (p = 0.045). Blood lactate concentration was similarly increased in all ROM (p < 0.001). Training at TOP ROM allowed not only to lift a higher load, but also to perform more repetitions with a lower rate of decline in mean barbell velocity. Despite the lower absolute load and work per repetition, fatigue was higher in BOTTOM than TOP and this may be attributed to differences in muscle length.

The Relationship Between Isometric and Dynamic Strength Following Resistance Training: A Systematic Review, Meta-Analysis, and Level of Agreement

BACKGROUND

Maximal lower-body strength can be assessed both dynamically and isometrically; however, the relationship between the changes in these 2 forms of strength following resistance training is not well understood.

PURPOSE

To systematically review and analyze the effects of resistance training on changes in maximal dynamic (1-repetition-maximum back squat, deadlift, and power clean) and position-matched isometric strength (isometric midthigh pull and the isometric squat). In addition, individual-level data were used to quantify the agreement and relationship between changes in dynamic and isometric strength.

METHODS

Databases were systematically searched to identify eligible articles, and meta-analysis procedures were performed on the extracted data. The raw results from 4 studies were acquired, enabling bias and absolute reliability measures to be calculated using Bland-Altman test of agreement.

RESULTS

Eleven studies met the inclusion criteria, which resulted in 29 isometric-dynamic change comparisons. The overall pooled effect was 0.13 in favor of dynamic testing; however, the prediction interval ranged from g = -0.49 to 0.75. There was no evidence of bias (P = .825) between isometric and dynamic tests; however, the reliability coefficient was estimated to be 16%, and the coefficient of variation (%) was 109.27.

CONCLUSIONS

As a range of future effects can be expected when comparing isometric to dynamic strength changes following resistance training, and limited proportionality exists between changes in these 2 strength qualities, there is strong evidence that isometric and dynamic strength represent separate neuromuscular domains. These findings can be used to inform strength-assessment models in athlete populations.

Comparison of the effects of long-lasting static stretching and hypertrophy training on maximal strength, muscle thickness and flexibility in the plantar flexors

Maximal strength measured via maximal voluntary contraction is known as a key factor in competitive sports performance as well as injury risk reduction and rehabilitation. Maximal strength and hypertrophy are commonly trained by performing resistance training programs. However, literature shows that long-term, long-lasting static stretching interventions can also produce significant improvements in maximal voluntary contraction. The aim of this study is to compare increases in maximal voluntary contraction, muscle thickness and flexibility after 6 weeks of stretch training and conventional hypertrophy training. Sixty-nine (69) active participants (f = 30, m = 39; age 27.4 ± 4.4 years, height 175.8 ± 2.1 cm, and weight 79.5 ± 5.9 kg) were divided into three groups: IG1 stretched the plantar flexors continuously for one hour per day, IG2 performed hypertrophy training for the plantar flexors (5 × 10-12 reps, three days per week), while CG did not undergo any intervention. Maximal voluntary contraction, muscle thickness, pennation angle and flexibility were the dependent variables. The results of a series of two-way ANOVAs show significant interaction effects (p < 0.05) for maximal voluntary contraction (ƞ2 = 0.143-0.32, p < 0.006), muscle thickness (ƞ2 = 0.11-0.14, p < 0.021), pennation angle (ƞ2 = 0.002-0.08, p = 0.077-0.625) and flexibility (ƞ2 = 0.089-0.21, p < 0.046) for both the stretch and hypertrophy training group without significant differences (p = 0.37-0.99, d = 0.03-0.4) between both intervention groups. Thus, it can be hypothesized that mechanical tension plays a crucial role in improving maximal voluntary contraction and muscle thickness irrespective whether long-lasting stretching or hypertrophy training is used. Results show that for the calf muscle, the use of long-lasting stretching interventions can be deemed an alternative to conventional resistance training if the aim is to increase maximal voluntary contraction, muscle thickness and flexibility. However, the practical application seems to be strongly limited as a weekly stretching duration of up to 7 h a week is opposed by 3 × 15 min of common resistance training.

Strength capacity of lower-limb muscles in world-class cyclists: new insights into the limits of sprint cycling performance

This study aimed to determine the relationship between the torque-generating capacity in sprint cycling and the strength capacity of the six lower-limb muscle groups in male and female world-class sprint cyclists. Eleven female and fifteen male top-elite cyclists performed 5-s sprints at maximal power in seated and standing positions. They also performed a set of maximal voluntary ankle, knee and hip flexions and extensions to assess single-joint isometric and isokinetic torques. Isokinetic torques presented stronger correlations with cycling torque than isometric torques for both body positions, regardless of the group. In the female group, knee extension and hip flexion torques accounted for 81.2% of the variance in cycling torque, while the ability to predict cycling torque was less evident in males (i.e., 59% of variance explained by the plantarflexion torque only). The standing condition showed higher correlations than seated and a better predictive model in males (R² = 0.88). In addition to the knee extensors and flexors and hip extensors, main power producers, the strength capacity of lower-limb distal plantarflexor (and to a lesser extent dorsiflexor) muscles, as well as other non-measured qualities (e.g., the upper body), might be determinants to produce such extremely high cycling torque in males.

Maximal strength measurement: A critical evaluation of common methods-a narrative review

Measuring maximal strength (MSt) is a very common performance diagnoses, especially in elite and competitive sports. The most popular procedure in test batteries is to test the one repetition maximum (1RM). Since testing maximum dynamic strength is very time consuming, it often suggested to use isometric testing conditions instead. This suggestion is based on the assumption that the high Pearson correlation coefficients of r ≥ 0.7 between isometric and dynamic conditions indicate that both tests would provide similar measures of MSt. However, calculating r provides information about the relationship between two parameters, but does not provide any statement about the agreement or concordance of two testing procedures. Hence, to assess replaceability, the concordance correlation coefficient (ρ c) and the Bland-Altman analysis including the mean absolute error (MAE) and the mean absolute percentage error (MAPE) seem to be more appropriate. Therefore, an exemplary model based on r = 0.55 showed ρ c = 0.53, A MAE of 413.58 N and a MAPE = 23.6% with a range of -1,000-800 N within 95% Confidence interval (95%CI), while r = 0.7 and 0.92 showed ρ c = 0.68 with a MAE = 304.51N/MAPE = 17.4% with a range of -750 N-600 N within a 95% CI and ρ c = 0.9 with a MAE = 139.99/MAPE = 7.1% with a range of -200-450 N within a 95% CI, respectively. This model illustrates the limited validity of correlation coefficients to evaluate the replaceability of two testing procedures. Interpretation and classification of ρ c, MAE and MAPE seem to depend on expected changes of the measured parameter. A MAPE of about 17% between two testing procedures can be assumed to be intolerably high.

Prolonged loss of force and power following fatiguing contractions in rat soleus muscles. Is low-frequency fatigue an issue during dynamic contractions?

Low-frequency fatigue (LFF) is defined by a relatively larger deficit in isometric force elicited by low-frequency electrical stimulation compared with high-frequency stimulation. However, the effects of LFF on power during dynamic contractions elicited at low and high frequencies have not been thoroughly characterized. In the current study, rat soleus muscles underwent fatiguing either concentric, eccentric, or isometric contractions. Before and 1 h after the fatiguing contractions, a series of brief isometric and dynamic contractions elicited at 20 and 80 Hz stimulation to establish force-velocity relationships. Maximal force (Fmax), velocity (Vmax), and power (Pmax) were assessed for each frequency. Sarcoplasmic reticulum (SR) Ca2+ release and reuptake rates were assessed pre- and postfatigue. Prolonged fatigue was observed as a loss of Fmax and Pmax in muscles fatigued by concentric or eccentric, but not by isometric contractions. When quantified as a decrease in the ratio between 20 Hz and 80 Hz contractile output, LFF was more pronounced for isometric force than for power (−21% vs. −16% for concentrically fatigued muscles, P = 0.003; 29 vs. 13% for eccentrically fatigued muscles, P < 0.001). No changes in SR Ca2+ release or reuptake rates were observed. We conclude that LFF is less pronounced when expressed in terms of power deficits than when expressed in terms of force deficits, and that LFF, therefore, likely affects performance to a lesser degree during fast concentric contractions than during static or slow contractions.

Despite Good Correlations, There Is No Exact Coincidence between Isometric and Dynamic Strength Measurements in Elite Youth Soccer Players

Speed strength performances are substantially dependent on maximum strength. Due to their importance, various methods have been utilized to measure maximum strength (e.g., isometric or dynamic) with discussed differences regarding transferability to sport-specific movements dependent upon the testing procedure. The aim of this study was to analyze whether maximum isometric force (MIF) during isometric back squats correlates with maximum strength measurements of the one repetition maximum (1RM) in the squat, with countermovement jump (CMJ) performance, and with drop jump (DJ) performances in elite youth soccer players (n = 16, 18.4 ± 1.5 [range: 17-23] years old). Additionally, concordance correlation coefficients (CCC, [ρc]) between isometric and dynamic measurements were calculated to verify whether one measurement can actually reproduce the results of the other. To improve comprehension, differences between isometric and dynamic testing values were illustrated by providing differences between both testing conditions. For this, the mean absolute error (MAE) and the mean absolute percentage error (MAPE) were calculated. To reach equality in scale, the 1RM measures were multiplicated by 9.81 to obtain a value of N. The 1RM demonstrated correlations of τ = |0.38| to |0.52| with SJ and CMJ performances, while MIF demonstrated correlations of τ = |0.21| to |0.32|. However, the correlations of both 1RM and MIF with the DJ reactive strength index (RSI = jump height /contact time) from different falling heights were of no statistical significance. The data showed significant correlations between both the absolute (τ = |0.54|) and the relative (τ = |0.40|) performances of 1RM and MIF, which were confirmed by CCC of ρc= |0.56| to |0.66|, respectively. Furthermore, the MAE and MAPE showed values of 2080.87 N and 67.4%, respectively. The data in this study show that, despite good correlations, there is no exact coincidence between isometric and dynamic strength measurements. Accordingly, both measurements may only represent an estimation of maximal strength capacity and cannot be substituted for each other. Therefore, maximal strength should be tested by using high similarity in the contraction condition, as it is used in the training process to counteract underestimation in strength because of unfamiliarity with the testing condition.

Influence of Long-Lasting Static Stretching on Maximal Strength, Muscle Thickness and Flexibility

Background: In animal studies long-term stretching interventions up to several hours per day have shown large increases in muscle mass as well as maximal strength. The aim of this study was to investigate the effects of a long-term stretching on maximal strength, muscle cross sectional area (MCSA) and range of motion (ROM) in humans.

Methods: 52 subjects were divided into an Intervention group (IG, n = 27) and a control group (CG, n = 25). IG stretched the plantar flexors for one hour per day for six weeks using an orthosis. Stretching was performed on one leg only to investigate the contralateral force transfer. Maximal isometric strength (MIS) and 1RM were both measured in extended knee joint. Furthermore, we investigated the MCSA of IG in the lateral head of the gastrocnemius (LG) using sonography. Additionally, ROM in the upper ankle was investigated via the functional “knee to wall stretch” test (KtW) and a goniometer device on the orthosis. A two-way ANOVA was performed in data analysis, using the Scheffé Test as post-hoc test.

Results: There were high time-effects (p = 0.003, ƞ² = 0.090) and high interaction-effect (p < 0.001, ƞ²=0.387) for MIS and also high time-effects (p < 0.001, ƞ²=0.193) and interaction-effects (p < 0.001, ƞ²=0,362) for 1RM testing. Furthermore, we measured a significant increase of 15.2% in MCSA of LG with high time-effect (p < 0.001, ƞ²=0.545) and high interaction-effect (p=0.015, ƞ²=0.406). In ROM we found in both tests significant increases up to 27.3% with moderate time-effect (p < 0.001, ƞ²=0.129) and high interaction-effect (p < 0.001, ƞ²=0.199). Additionally, we measured significant contralateral force transfers in maximal strength tests of 11.4% (p < 0.001) in 1RM test and 1.4% (p=0.462) in MIS test. Overall, there we no significant effects in control situations for any parameter (CG and non-intervened leg of IG).

Discussion: We hypothesize stretching-induced muscle damage comparable to effects of mechanical load of strength training, that led to hypertrophy and thus to an increase in maximal strength. Increases in ROM could be attributed to longitudinal hypertrophy effects, e.g., increase in serial sarcomeres. Measured cross-education effects could be explained by central neural adaptations due to stimulation of the stretched muscles.

Evaluation of the Isometric and Dynamic Rates of Force Development in Multi-Joint Muscle Actions

The rate of force development (RFD) in the isometric leg press (ILP), the countermovement jump (CMJ) and the squat jump (SJ) were examined in twenty-three (9 females) team sport athletes aged 21-24 years. Peak force (Fpeak), peak rate of force development (RFDpeak) and RFD at different time epochs (0-50, 50-100, 100-150, 150-200) were calculated from the force-time curve, as well as CMJ and SJ height and the center of mass displacement. RFDpeak, RFD at 0-50, 50-100 and 100-150 ms and Fpeak were similar between the CMJ and the SJ (p = 0.26 to 0.99). Furthermore, RFD_{0-50 ms} was similar between the ILP, the CMJ, and the SJ (p = 0.99 to 0.57). Higher values were observed in the ILP compared with the CMJ and the SJ in RFD_{50-100 ms} and RFD_{100-150 ms} (p < 0.001) and these differences were maintained even when RFD was scaled to body mass. The higher RFD normalized to Fpeak was attained at the 50-100 ms time interval with no differences between the ILP, CMJ and SJ and between males and females. These results suggest that the ability to exert rapid force is similar between the CMJ and the SJ, irrespective of the type of muscle action. Furthermore, RFD normalized to Fpeak is a muscle-force independent index of explosive force production, facilitating comparisons between individuals with different levels of muscle strength. The similarities between the CMJ and the SJ in RFDpeak, Fpeak, and RFD at different time epochs may imply that these types of jumps could be used interchangeably to assess explosive lower limb performance.

Muscle volume vs. anatomical cross-sectional area: Different muscle assessment does not affect the muscle size-strength relationship

Muscle volume (MV) and anatomical cross-sectional area (CSA) are used as measures of muscle-size, but determining these from magnetic resonance imaging (MRI) is a very time-consuming process. Additionally, it is unclear if the use of different muscle size assessments (all vs. reduced number of slices images) would impact the muscle size-strength relationship. Thus, this study aimed to investigate if muscle size calculation by using a reduced or all slices images from pectoralis major (PM) would maintain a similar muscle size-strength relationship with bilateral maximal dynamic and isometric contractions on a bench press exercise. Twenty-four healthy males underwent an MRI examination to measure PM muscle size, and maximal isometric and dynamic contractions (by one repetition maximum, 1RM) were performed. Correlations between maximal isometric voluntary force (MVF) and dynamic strength (1RM) with muscle size variables [three images from the largest part of PM (CSA_3MAX), three images accounting for the shape -first image, middle image, final image- of the PM (CSA₃), and MV] were performed. The correlation between 1RM with MV, CSA₃, and CSA_3MAX were 0.84, 0.832, and 0.727 (p < 0.001), respectively. The correlation between MVF with MV, CSA₃, and CSA_3MAX were 0.738, 0.733, and 0.604 (p < 0.001), respectively. Overall, PM MV and CSA₃ exhibit a stronger and similar muscle size-strength relationship during maximal dynamic and isometric tests than CSA_3MAX. Therefore, a reduced number of slices (CSA₃) could be used as an alternative to considerably reduce the time of analysis without compromise muscle size-strength relationship.

Association Between Lower Trapezius Isometric Strength and Y-Balance Test Upper Quarter Performance in College Volleyball Players

CONTEXT

Knowing the possible association between the isometric strength of the shoulder rotators, scapular muscles, and the Y-balance test upper quarter (YBT-UQ) performance could help identify which indicators of shoulder stability should be considered in this field test. This study aimed to determine whether the isometric strength of the shoulder rotators and scapular muscles is associated with the YBT-UQ performance of the dominant upper limb in amateur volleyball players.

DESIGN

Cross-sectional study.

METHODS

A convenience sample of 22 male and 18 female volleyball players (≥12 h of training/week) between 18 and 26 years of age. The isometric strength of the middle trapezius, lower trapezius, serratus anterior, internal, and external rotator muscles was assessed with a handheld dynamometer. Participants performed the YBT-UQ in the superolateral, medial, and inferolateral directions. The absolute isometric peak force (in Newtons) was normalized to body weight (in Newtons per kilogram) for each muscle test. For each YBT-UQ direction, the distance (in centimeters) was normalized for upper limb length (in percentage). A backward multiple linear regression analysis was used to determine the associations between variables.

RESULTS

The analysis revealed that the isometric strength of the lower trapezius (β = 26.82; 95% confidence interval, 21.24-32.40) is associated with inferolateral YBT-UQ performance (adjusted R2 = .706; P < .001). This factor explains 70% of the variability of the YBT-UQ in the inferolateral direction.

CONCLUSIONS

Lower trapezius isometric strength is associated with inferolateral YBT-UQ performance of the dominant upper limb in amateur volleyball players. These findings could help in the development of more specific training programs and rehabilitation goals according to the performance of the athletes in the test.

Static and dynamic evaluation of respiratory muscle strength in asthmatic children and adolescents

Abstract Objectives: to evaluate static and dynamic respiratory muscle strength in children and adolescents with asthma. Methods: cross-sectional study, involving 80 children and adolescents, 40 with asthma and 40 healthy controls. Biological and clinical characteristics were analyzed. The analysis of the dynamic inspiratory muscle strength was obtained using the KH5 device of the POWERbreathe® line, while the static evaluation was performed using an analog manova-cuometer. Results: the mean obtained from the S-Index was higher in the control group compared to asthmatics (p = 0.026). There was no statistical difference between MIP values for asthmatics and predicted values (p = 0.056). The MEP results showed a significant difference between the mean of the cases and the predicted values (p = 0.000). There was a positive correlation between height and S-Index (p = 0.002 and r = 0.438). Conclusion: the present study demonstrated that the static inspiratory muscle strength (PImáx) of children and adolescents with asthma in comparison with the values predicted in the literature does not differ, however, when submitted to dynamic assessment (S-Index), it presents higher values in healthy controls. In addition, the S-Index showed a positive correlation with the child's height.

Relationship Between Isometric Force-Time Characteristics and Sprint Kayaking Performance

Force-time characteristics obtained during isometric strength tests are significantly correlated to various sporting movements. However, data on the relationship between isometric force-time characteristics and sprint kayaking performance are lacking in the literature.

PURPOSE

The purpose of the study was, therefore, to investigate the relationship between sprint kayaking performance with ergometer performance and measures from 3 isometric strength tests: isometric squat, isometric bench press, and isometric prone bench pull.

METHODS

A total of 23 sprint kayaking athletes performed all 3 tests, at 90° and 120° knee angles for isometric squat and at elbow angles for isometric bench press and isometric prone bench pull, and a 200-m sprint on-water to attain the fastest time-to-completion (OWTT) possible and on a kayak ergometer to attain the highest mean power (LABTT) possible.

RESULTS

There was a significant inverse correlation between OWTT and LABTT (r = -.90, P < .001). The peak forces achieved from all isometric strength tests were significantly correlated with time-to-completion for OWTT and mean power for LABTT (r = -.44 to -.88, P < .05 and .47 to .80, P < .05, respectively). OWTT was significantly correlated with the peak rate of force development during all isometric tests except for the isometric squat at a 120° knee angle (r = -.47 to -.62, P < .05). LABTT was significantly correlated with peak rate of force development from the isometric bench press and isometric prone bench pull (r = .64-.86, P < .01).

CONCLUSION

Based on the observed strong correlations, the mean power attained during LABTT is a good predictor of OWTT time-to-completion. Furthermore, upper- and lower-body maximum strength and peak rate of force development are equally important for on-water and ergometer sprint kayaking performance.

Concurrent Validity of the Static and Dynamic Measures of Inspiratory Muscle Strength: Comparison between Maximal Inspiratory Pressure and S-Index

Objective

To verify the concurrent validity between the inspiratory muscle strength (IMS) values obtained in static (maximal inspiratory pressure [MIP]) and dynamic (S-Index) assessments.

Methods

Healthy individuals were submitted to two periods of evaluation: i) MIP, static maneuver to obtain IMS, determined by the Mueller’s maneuver from residual volume (RV) until total lung capacity (TLC); ii) and S-Index, inspiration against open airway starting from RV until TLC. Both measures were performed by the same evaluator and the subjects received the same instructions. Isolated maneuvers with differences < 10% were considered as reproducible measures.

Results

Data from 45 subjects (21 males) were analyzed and that showed statistical difference between MIP and S-Index values (133.5 ± 33.3 and 125.6 ± 32.2 in cmH2O, respectively), with P=0.014. Linear regression showed r²=0.54 and S-Index prediction formula = 39.8+(0.75×MIP). Pearson’s correlation demonstrated a strong and significant association between the measures with r=0.74. The measurements showed good concordance evidenced by the Bland-Altman test.

Conclusion

S-Index and MIP do not present similar values since they are evaluations of different events of the muscular contraction. However, they have a strong correlation and good agreement, which indicate that both are able to evaluate the IMS of healthy individuals.

Introduction of dynamic rate-of-force development scaling factor in progressive drop jumps

Rapid force generation across submaximal levels has been evaluated with the rate of force development scaling factor (RFD-SF) in different isometric tasks, while such measurement was still not verified in dynamic tasks. Our study was designed to evaluate the feasibility of the RFD-SF in dynamic drop jump (DJ) task (RFD-SF_DJ). A total of 55 young athletes performed isometric plantarflexion at different submaximal intensities and 60 DJs (6 different drop heights). For each participant we calculated linearity (r²) and slope in isometric task (RFD-SF_PF), eccentric part of DJ (RFD-SF_DJ-ECC) and concentric part of DJ (RFD-SF_DJ-CON), as well as average jump height (DJ_H) from each drop height. Our results revealed strong linear force-RFD relationship for isometric plantarflexion (r² = 0.90 ± 0.06), eccentric (r² = 0.87 ± 0.09) and concentric phase of DJ (r² = 0.80 ± 0.18). Significant moderate positive correlations were calculated between RFD-SF_PF and RFD-SF_DJ-ECC (r = 0.311, p < 0.05) and small negative correlations between RFD-SF_DJ-CON and RFD-SF (r = -0.276, p < 0.05)_. Significant positive moderate correlations were seen only between RFD-SF_DJ-ECC and DJ_H from 10 cm (r = 0.459, p < 0.001) and 15 cm (r = 0.423, p < 0.01). This is the first study to introduce and confirm that RFD-SF_DJ can be obtained from the multi-joint tasks (60 jumps) and still provide acceptable reliability and linear relationship. Furthermore, RFD-SF_DJ may have greater practical application than RFD-SF assessed under the isometric conditions. This verification of RFD-SF_DJ opens opportunities for further research regarding its practical application.

Is Handgrip Strength a Useful Measure to Evaluate Lower Limb Strength and Functional Performance in Older Women?

Aim

This study aimed to determine the association of handgrip strength with isometric and isokinetic strength (hip, knee and ankle extensor/flexor muscles), and functional capacity in older women.

Methods

The handgrip strength and lower limb strength of 199 older women (60–86 years) were measured using JAMAR and BIODEX dynamometers, respectively. Time Up and Go, Five-times-sit-to-stand and 6m-walk functional tests were evaluated. Pearson correlations were used to determine the relationship between variables. Regression analysis was applied to identify if HS was able to predict TUG performance. The effect of age was analyzed by splitting the participants in a group of older women (OLD; from 60 to 70 years old) and very old women (from 71 to 86 years old).

Results

The HS and isometric/isokinetic strength correlations were negligible/low and, in most cases, were non-significant. The correlation between handgrip strength and functional tests also ranged predominantly from negligible (r=0.0 to 0.3) to low (r=0.3 to 0.5), irrespective of the group age. The handgrip strength was not able to explain the variance of the TUG performance.

Conclusion

Generalizing handgrip strength as a practical and straightforward measure to determine lower limbs and overall strength, and functional capacity in older women must be viewed with caution. Handgrip strength and standard strength measures of the lower limbs and functional tests present a negligible/low correlation.

Association Between Performance in Muscle Fitness Field Tests and Skeletal Muscle Mass in Soldiers

INTRODUCTION

Muscle strength and muscle endurance are important fitness components related to safe and efficient execution of physically demanding military work. In soldiers, these components are traditionally measured from simple field tests like push-ups, sit-ups, and pull-ups. However, the validity of such muscle fitness field tests is questioned due to reports of low association between test performance and the ability to conduct strength demanding military work (eg, lift and carry tasks). It is therefore necessary to study, develop, and implement more valid field tests, which are still feasible for mass testing in the military. Skeletal muscle mass (SMM) is an important physiological component related to maximal muscle force generation (strength). Thus, an alternative way of validating muscle fitness field tests is by comparisons against SMM. The purpose of the present study was to investigate the association between SMM and performance in five muscle fitness field tests.

MATERIALS AND METHODS

A total of 275 military cadets (including 27 women) participated in this method comparison study. The field tests included push-ups, sit-ups, pull-ups (vertical for men, horizontal for women), standing medicine ball throw, and Sargent jump (peak power and jump height). SMM was estimated from bioelectrical impedance analysis and expressed in absolute values (kg) or relative to body mass. Pearson correlation coefficients (r) were calculated to investigate associations between SMM and performance in the five field tests. The study was submitted to the Regional Committee for Medical and Health Research Ethics prior to startup, and the Committee considered the study to be exempted from notification. The study was reviewed and approved by the Norwegian Social Science Data Services.

RESULTS

In men, the highest correlation against absolute SMM was found for the Sargent jump (peak power) and the medicine ball throw (r = 0.71 and 0.54, respectively). The same trend was evident for women (r = 0.85 and 0.61, respectively) and for the two genders combined (r = 0.85 and 0.79, respectively). All these r-values were significant (P < 0.001). In men, the highest r against relative SMM was found for pull-ups (r = 0.50, P < 0.001). The same pattern was found in women, but the association was not significant (r = 0.36, P = 0.07). The sit-ups test demonstrated low or nonsignificant associations with both absolute and relative SMM.

CONCLUSIONS

Among the five muscle fitness field tests investigated, the Sargent jump (peak power) and the medicine ball throw demonstrated the strongest correlation coefficients against absolute SMM. Thus, these two tests should be better alternatives for assessing relevant upper and lower body strength and power in soldiers compared with push-ups, pull-ups, and sit-ups. Pull-ups generally demonstrated the strongest correlation against relative SMM. Sit-ups demonstrated low or nonsignificant associations with both absolute and relative SMM. Consequently, the test should be considered for removal from military fitness test batteries or replaced by alternative abdominal tests that are more valid.

The Relationship between Isometric Force-Time Characteristics and Dynamic Performance: A Systematic Review

The purpose of this article was to review the data on the relationship between multi-joint isometric strength test (IsoTest) force-time characteristics (peak force, rate of force development and impulse) and dynamic performance that is available in the current literature. Four electronic databases were searched using search terms related to IsoTest. Studies were considered eligible if they were original research studies that investigated the relationships between multi-joint IsoTest and performance of dynamic movements; published in peer-reviewed journals; had participants who were athletes or active individuals who participate in recreational sports or resistance training, with no restriction on sex; and had full text available. A total of 47 studies were selected. These studies showed significant small to large correlations between isometric bench press (IBP) force-time variables and upper body dynamic performances (r² = 0.221 to 0.608, p < 0.05) and significant small to very large correlation between isometric squat (ISqT) (r² = 0.085 to 0.746, p < 0.05) and isometric mid-thigh pull (IMTP) (r² = 0.120 to 0.941, p < 0.05) force-time variables with lower body dynamic performances. IsoTest force-time characteristics were shown to have small to very large correlations with dynamic performances of the upper and lower limbs as well as performance of sporting movements (r² = 0.118 to 0.700, p < 0.05). These data suggest that IsoTest force-time characteristics provide insights into the force production capability of athletes which give insight into dynamic performance capabilities.

Comparison of anthropometric profile and handgrip strength between inter-university volleyball players and a reference group

Study aim: In a volleyball game, multiple elements can influence competitive success, e.g. height, arm span and other anthropometric variables. The present cross-sectional study was undertaken to find out whether any differences exist between Indian inter-university male and female volleyball players as well as between players and a reference group in terms of anthropometry and handgrip strength.

Materials and methods: The present cross-sectional research was conducted on 114 randomly selected Indian inter-university male (n = 50) and female (n = 64) volleyball players aged 18–25 years. An equal number of reference group individuals who did not participate in any exercise or training programme were also taken. Height, body weight, body mass index (BMI) (kg/m2), hand length, hand breadth, second digit length, fourth digit length, second and fourth digit ratio (2D/4D ratio), upper arm length, forearm length, total arm length, upper arm circumference, hip circumference; humerus and femur biepicondylar diameters, handgrip strength (dominant/non-dominant), arm muscle area, arm area, arm fat area, arm fat index, % body fat, and % lean body mass were measured with equipment including an anthropometer, sliding caliper, handgrip dynamometer and skinfold caliper using standard techniques. The data were analysed using SPSS version 17.0. Student’s t-test was applied for the comparison of data between players and the reference group. Differences between the groups were analysed using the oneway ANOVA test. Bonferroni post hoc test was applied after application of the ANOVA test. Effect size was also calculated. Statistical significance (p < 0.05) was indicated using a 5% level of probability.

Results: Male volleyball players had higher mean values in height, body weight, hand length, hand breadth, second and fourth digit length, dominant and non-dominant handgrip strength, humerus and femur biepicondylar diameter, upper arm length, forearm length and total arm length, arm muscle area, arm area and percent lean body mass than the reference group. Similar findings were observed between female players and the reference group also. Statistically significant differences (p < 0.05–0.001) were also observed between male and female players except BMI, 2D/4D ratio, and arm fat area. These findings were supported by the effect size (η) calculations.

Conclusion: Volleyball players had better height, weight, hand and arm anthropometrics, handgrip strength and % lean body mass as compared to the reference group. Significant differences were found in anthropometry and handgrip strength between players and reference group individuals, suggesting that these findings could be very useful for player selection and talent identification in sports.

Effects of Knee Position on the Reliability and Production of Maximal and Rapid Strength Characteristics During an Isometric Squat Test

This study aimed to examine the effects of knee position on the reliability and production of peak force (PF) and rate of force development (RFD) characteristics during an isometric squat. Fourteen resistance-trained females performed isometric squats at 90, 120, and 150° knee angles (corresponding to parallel, half, and quarter squat positions, respectively) on 2 different occasions, from which PF, peak RFD, and early (RFD30, RFD50, RFD100) and late (RFD200) phase RFD variables were extracted. PF and RFD200 were highly consistent across trials for all 3 squat positions, with intraclass correlation coefficients (ICCs) ranging between 0.812-0.904 and coefficients of variation (CVs) between 6.6-19.4%. For peak and early RFD characteristics, higher ICCs and lower CV values were observed for the quarter squat (ICCs = 0.818-0.852, CVs = 17.3-19.4%) compared to the parallel (ICCs = 0.591-0.649, CVs = 30.1-55.9%) and half squats (ICCs = 0.547-0.598,CVs = 31.1-34.2%). In addition, isometric PF and RFD200 increased (P ≤ .001-0.04) with squat position (parallel < half < quarter); however, there were no differences for peak RFD (P ≥ .27), RFD30 (P ≥ .99), RFD50 (P ≥ .99), and RFD100 (P ≥ .09). These findings suggest that performing isometric squats at higher (150°) rather than lower knee joint angles (90-120°) may provide for an improved capacity to produce greater PF and RFD200 as well as a more reliable testing position for measuring peak and early RFD characteristics.

Core and skin temperature influences on the surface electromyographic responses to an isometric force and position task

The large body of work demonstrating hyperthermic impairment of neuromuscular function has utilized maximal isometric contractions, but extrapolating these findings to whole-body exercise and submaximal, dynamic contractions may be problematic. We isolated and compared core and skin temperature influences on an isometric force task versus a position task requiring dynamic maintenance of joint angle. Surface electromyography (sEMG) was measured on the flexor carpi radialis at 60% of baseline maximal voluntary contraction while either pushing against a rigid restraint (force task) or while maintaining a constant wrist angle and supporting an equivalent inertial load (position task). Twenty participants performed each task at 0.5°C rectal temperature (T_re) intervals while being passively heated from 37.1±0.3°C to ≥1.5°C T_re and then cooled to 37.8±0.3°C, permitting separate analyses of core versus skin temperature influences. During a 3-s contraction, trend analysis revealed a quadratic trend that peaked during hyperthermia for root-mean-square (RMS) amplitude during the force task. In contrast, RMS amplitude during the position task remained stable with passive heating, then rapidly increased with the initial decrease in skin temperature at the onset of passive cooling (p = 0.010). Combined hot core and hot skin elicited shifts toward higher frequencies in the sEMG signal during the force task (p = 0.003), whereas inconsistent changes in the frequency spectra occurred for the position task. Based on the patterns of RMS amplitude in response to thermal stress, we conclude that core temperature was the primary thermal afferent influencing neuromuscular response during a submaximal force task, with minimal input from skin temperature. However, skin temperature was the primary thermal afferent during a position task with minimal core temperature influence. Therefore, temperature has a task-dependent impact on neuromuscular responses.

Upper-Body Strength Measures and Pop-Up Performance of Stronger and Weaker Surfers

Parsonage, J, Secomb, JL, Sheppard, JM, Ferrier, BK, Dowse, RA, and Nimphius, S. Upper-body strength measures and pop-up performance of stronger and weaker surfers. J Strength Cond Res 34(10): 2982-2989, 2020-The primary purpose of this study was to investigate the reliability of the isometric push-up (IPU), dynamic push-up (DPU), and force plate pop-up (FP POP) as measures of upper-body isometric and dynamic strength qualities in surfing athletes. Furthermore, the study aimed to compare pop-up performance between stronger and weaker surfers. Eighteen female (n = 9) and male (n = 9) surfers (age = 28.1 ± 6.4 years, mass = 69.6 ± 10.4 kg, and height = 172.5 ± 6.7 cm) completed a battery of upper-body strength assessments, of which exhibited high between-day reliability: IPU, (coefficient of variation [CV%] = 4.7, intraclass correlation coefficient [ICC] = 0.96), DPU (CV% = 5.0, ICC = 0.90), and FP POP (CV% = 4.4, ICC = 0.90). Participants were subsequently split into stronger (n = 9) and weaker (n = 9) surfers based on normalized peak force (PF) attained in the IPU. Pop-up performance was measured both in the water and during the FP POP and was referred to as time to pop-up (TTP). Significant between-group differences were observed for normalized PF during IPU (d = 1.59, p < 0.01) and DPU (d = 0.94 p = 0.04). Although not significant, there was a large magnitude difference in FP POP (d = 0.80, p = 0.08) and FP TTP (d = 0.85, p = 0.07). Significant correlations were identified between normalized IPU PF and normalized DPU FP (r = 0.69, p = 0.03) and FP TTP (r = 0.73, p = 0.02) in the stronger group. The weaker group exhibited a significant inverse correlation between normalized IPU PF and in-water TTP (r = -0.77, p < 0.01). The results suggest improvements in pop-up performance may be elicited by improving dynamic strength for stronger surfers, whereas pop-up performance in weaker surfers may be elicited by improving maximum strength. The upper-body strength assessments provided a novel insight into strength qualities that are associated with in-water performance of surfers (TTP).

Cluster analysis of novel isometric strength measures produces a valid and evidence-based classification structure for wheelchair track racing

Background

The Para athletics wheelchair-racing classification system employs best practice to ensure that classes comprise athletes whose impairments cause a comparable degree of activity limitation. However, decision-making is largely subjective and scientific evidence which reduces this subjectivity is required.

Aim

To evaluate whether isometric strength tests were valid for the purposes of classifying wheelchair racers and whether cluster analysis of the strength measures produced a valid classification structure.

Methods

Thirty-two international level, male wheelchair racers from classes T51–54 completed six isometric strength tests evaluating elbow extensors, shoulder flexors, trunk flexors and forearm pronators and two wheelchair performance tests–Top-Speed (0–15 m) and Top-Speed (absolute). Strength tests significantly correlated with wheelchair performance were included in a cluster analysis and the validity of the resulting clusters was assessed.

Results

All six strength tests correlated with performance (r=0.54–0.88). Cluster analysis yielded four clusters with reasonable overall structure (mean silhouette coefficient=0.58) and large intercluster strength differences. Six athletes (19%) were allocated to clusters that did not align with their current class. While the mean wheelchair racing performance of the resulting clusters was unequivocally hierarchical, the mean performance of current classes was not, with no difference between current classes T53 and T54.

Conclusions

Cluster analysis of isometric strength tests produced classes comprising athletes who experienced a similar degree of activity limitation. The strength tests reported can provide the basis for a new, more transparent, less subjective wheelchair racing classification system, pending replication of these findings in a larger, representative sample. This paper also provides guidance for development of evidence-based systems in other Para sports.

Muscle Function in Osteogenesis Imperfecta Type IV

Results of previous studies suggest that children and adolescents with osteogenesis imperfecta (OI) type IV have muscle force deficits. However, muscle function remains to be objectively quantified in this population. This study aimed to assess upper and lower extremity muscle function in patients with OI type IV. It was carried out in the outpatient department of a pediatric orthopedic hospital; 27 individuals with OI type IV (7-21 years; 13 males), 27 age- and sex-matched individuals with OI type I, and 27 age- and sex-matched controls. Upper extremity muscle force was assessed with hydraulic hand dynamometry, and lower extremity muscle function (peak force per body weight and peak power per body mass) was measured by mechanography through five tests: multiple two-legged hopping, multiple one-legged hopping, single two-legged jump, chair-rise test, and heel-rise test. Upper-limb grip force was normal for patients with OI type IV when compared to height and sex reference data (average z-score = 0.17 ± 1.30; P = 0.88). Compared to age- and sex-matched controls, patients with OI type IV had approximately 30% lower-limb peak force and 50% peak power deficits (P values <0.05). At the lower-limb level, they had a 50% lower peak power than age- and sex-matched patients with OI type I (P < 0.05). Patients with OI type IV have normal upper-limb muscle force but a muscle function deficit at the lower-limb level. These results suggest that lower-limb muscle weakness may contribute to functional deficits in these individuals.

The use of the isometric squat as a measure of strength and explosiveness

The isometric squat has been used to detect changes in kinetic variables as a result of training; however, controversy exists in its application to dynamic multijoint tasks. Thus, the purpose of this study was to further examine the relationship between isometric squat kinetic variables and isoinertial strength measures. Subjects (17 men, 1-repetition maximum [1RM]: 148.2 ± 23.4 kg) performed squats 2 d · wk(-1) for 12 weeks and were tested on 1RM squat, 1RM partial squat, and isometric squat at 90° and 120° of knee flexion. Test-retest reliability was very good for all isometric measures (intraclass correlation coefficients > 0.90); however, rate of force development 250 milliseconds at 90° and 120° seemed to have a higher systematic error (relative technical error of measurement = 8.12%, 9.44%). Pearson product-moment correlations indicated strong relationships between isometric peak force at 90° (IPF 90°) and 1RM squat (r = 0.86), and IPF 120° and 1RM partial squat (r = 0.79). Impulse 250 milliseconds (IMP) at 90° and 120° exhibited moderate to strong correlations with 1RM squat (r = 0.70, 0.58) and partial squat (r = 0.73, 0.62), respectively. Rate of force development at 90° and 120° exhibited weak to moderate correlations with 1RM squat (r = 0.55, 0.43) and partial squat (r = 0.32, 0.42), respectively. These findings demonstrate a degree of joint angle specificity to dynamic tasks for rapid and peak isometric force production. In conclusion, an isometric squat performed at 90° and 120° is a reliable testing measure that can provide a strong indication of changes in strength and explosiveness during training.

Measures of functional performance and their association with hip and thigh strength

CONTEXT

Insufficient hip and thigh strength may increase an athlete's susceptibility to injury. However, screening for strength deficits using isometric and isokinetic instrumentation may not be practical in all clinical scenarios.

OBJECTIVE

To determine if functional performance tests are valid indicators of hip and thigh strength.

DESIGN

Descriptive laboratory study.

SETTING

Research laboratory.

PATIENTS OR OTHER PARTICIPANTS

Sixty-two recreationally athletic men (n = 30, age = 21.07 years, height = 173.84 cm, mass = 81.47 kg) and women (n = 32, age = 21.03 years, height = 168.77 cm, mass = 68.22 kg) participants were recruited.

INTERVENTION(S)

During session 1, we measured isometric peak force and rate of force development for 8 lower extremity muscle groups, followed by an isometric endurance test. During session 2, participants performed functional performance tests.

MAIN OUTCOME MEASURE(S)

Peak force, rate of force development, fatigue index, hop distance (or height), work (joules), and number of hops performed during the 30-second lateral-hop test were assessed. The r values were squared to calculate r (2). We used Pearson correlations to evaluate the associations between functional performance and strength.

RESULTS

In men, the strongest relationship was observed between triple-hop work and hip-adductor peak force (r(2) = 50, P ≤ .001). Triple-hop work also was related to hip-adductor (r(2) = 38, P ≤ .01) and hip-flexor (r(2) = 37, P ≤ .01) rate of force development. For women, the strongest relationships were between single-legged vertical-jump work and knee-flexor peak force (r(2) = 0.44, P ≤ .01) and single-legged vertical-jump height and knee-flexor peak force (r(2) = 0.42, P ≤ .01). Single-legged vertical-jump height also was related to knee-flexor rate of force development (r(2) = 0.49, P ≤ .001). The 30-second lateral-hop test did not account for a significant portion of the variance in strength endurance.

CONCLUSIONS

Hop tests alone did not provide clinicians with enough information to make evidence-based decisions about lower extremity strength in isolated muscle groups.

Reliability of a Novel Testing Protocol to Assess Upper-Body Strength Qualities in Elite Athletes

Purpose:

The purpose of this study was to evaluate the reliability of an isometric-bench-press (IBP) test performed across 4 elbow angles and a ballistic bench throw (BBT) using a relative load, as well as evaluating the reliability of the dynamic strength index (DSI: BBT peak force/IBP peak force).

Methods:

Twenty-four elite male athletes performed the IBP and a 45% 1-repetition-maximum BBT on 2 separate days with 48 h between testing occasions. Peak force, peak power, peak velocity, peak displacement, and peak rate of force development (PRFD) were assessed using a force plate and linear position transducer. Reliability was assessed by intraclass correlation (ICC), coefficient of variation (%CV) and typical error.

Results:

Performance measures in the BBT, such as peak force, peak velocity, peak power, and peak displacement, were considered reliable (ICC = .85–.92, %CV = 1.7–3.3), while PRFD was not (ICC = .43, %CV = 4.1). Similarly, for the IBP, peak force across all angles was considered reliable (ICC = .89–.97, %CV = 1.2–1.6), while PRFD was not (ICC = .56–.65, %CV = 0.5–7.6). The DSI was also reliable (ICC = .93, %CV = 3.5).

Conclusions:

Performance measures such as peak force in the IBP and BBT are reliable when assessing upper-body pressing-strength qualities in elite male athletes. Furthermore, the DSI is reliable and could potentially be used to detect qualities of relative deficiency and guide specific training interventions.

Muscle anatomy and dynamic muscle function in osteogenesis imperfecta type I

CONTEXT

Results of previous studies suggested that children and adolescents with osteogenesis imperfecta (OI) type I have a muscle force deficit. However, muscle function has only been assessed by static isometric force tests and not in more natural conditions such as dynamic force and power tests.

OBJECTIVE

The purpose of this study was to assess lower extremity dynamic muscle function and muscle anatomy in OI type I.

SETTING

The study was performed in the outpatient department of a pediatric orthopedic hospital.

PATIENTS AND OTHER PARTICIPANTS

A total of 54 individuals with OI type I (6-21 years; 20 male) and 54 age- and sex-matched controls took part in this study.

MAIN OUTCOME MEASURES

Calf muscle cross-sectional area and density were measured by peripheral quantitative computed tomography. Lower extremity muscle function (peak force per body weight and peak power per body mass) was measured by jumping mechanography through 5 tests: multiple two-legged hopping, multiple one-legged hopping, single two-legged jump, chair-rise test, and heel-rise test.

RESULTS

Compared with age- and sex-matched controls, patients with OI type I had smaller muscle size (P = .04) but normal muscle density (P = .21). They also had lower average peak force and lower specific force (peak force/muscle cross-sectional area; all P < .008). Average peak power was lower in patients with OI type I but not significantly so (all P > .054).

CONCLUSIONS

Children and adolescents with OI type I have, on average, a significant force deficit in the lower limb as measured by dynamic force tests. Nonetheless, these data also show that OI type I is compatible with normal muscle performance in some individuals.

Analysis of lower limb asymmetries by isokinetic and vertical jump tests in soccer players

Assessment of lower extremity bilateral asymmetries in soccer players is important for both injury prevention and performance. The purpose of this investigation was to compare isokinetic knee extensor assessment of asymmetry with a more specific countermovement jump (CMJ). Forty-six Brazilian male professional soccer players participated in this study. The maximal power, maximal force and impulse were determined during CMJ and the total work and peak torque at 60, 180, and 300°·s during isokinetic leg extension, separately for each leg. Factor analysis was performed for all investigated variables, and the diagnostic concordance between different criteria was analyzed by McNemar's χ test. The factor analysis showed that the isokinetic and CMJ tests were widely independent methods for the assessment of bilateral differences. Concordance of the diagnostic information could only be found between the maximal force during CMJ and the total work and peak torque at 180 and 300°·s during isokinetic leg extension. Impulse and maximal power during CMJ on a double force platform appear to be appropriate additional variables for the identification of bilateral differences. Therefore, it might be pertinent to perform, in addition to isokinetic assessment, a vertical jump test on a force platform to assure widespread and reliable diagnostic information.

Relationships between force-time characteristics of the isometric midthigh pull and dynamic performance in professional rugby league players

There is considerable conflict within the literature regarding the relevance of isometric testing for the assessment of neuromuscular function within dynamic sports. The aim of this study was to determine the relationship between isometric measures of force development and dynamic performance. Thirty-nine professional rugby league players participated in this study. Forty-eight hours after trial familiarization, participants performed a maximal isometric midthigh pull, with ∼120-130° bend at the knee, countermovement jump (CMJ), and a 10-m sprint. Force-time data were processed for peak force (PF), force at 100 milliseconds (F100ms), and peak rate of force development (PRFD). Analysis was carried out using Pearson's product moment correlation with significance set at p < 0.05. The PF was not related to dynamic performance; however, when expressed relative to body weight, it was significantly correlated with both 10-m time and CMJ height (r = -0.37 and 0.45, respectively, p < 0.05). The F100ms was inversely related to 10-m time (r = -0.54, p < 0.01); moreover, when expressed relative to body weight, it was significantly related to both 10-m time and CMJ height (r = -0.68 and 0.43, p < 0.01). In addition, significant correlations were found between PRFD and 10-m time (r = -0.66, p < 0.01) and CMJ height (r = 0.387, p < 0.01). In conclusion, this study provides evidence that measures of maximal strength and explosiveness from isometric force-time curves are related to jump and sprint acceleration performance in professional rugby league players.

Strength testing and training of rowers: a review

In the quest to maximize average propulsive stroke impulses over 2000-m racing, testing and training of various strength parameters have been incorporated into the physical conditioning plans of rowers. Thus, the purpose of this review was 2-fold: to identify strength tests that were reliable and valid correlates (predictors) of rowing performance; and, to establish the benefits gained when strength training was integrated into the physical preparation plans of rowers. The reliability of maximal strength and power tests involving leg extension (e.g. leg pressing) and arm pulling (e.g. prone bench pull) was high (intra-class correlations 0.82-0.99), revealing that elite rowers were significantly stronger than their less competitive peers. The greater strength of elite rowers was in part attributed to the correlation between strength and greater lean body mass (r = 0.57-0.63). Dynamic lower body strength tests that determined the maximal external load for a one-repetition maximum (1RM) leg press (kg), isokinetic leg extension peak force (N) or leg press peak power (W) proved to be moderately to strongly associated with 2000-m ergometer times (r = -0.54 to -0.68; p < 0.05). Repetition tests that assess muscular or strength endurance by quantifying the number of repetitions accrued at a fixed percentage of the strength maximum (e.g. 50-70% 1RM leg press) or set absolute load (e.g. 40 kg prone bench pulls) were less reliable and more time consuming when compared with briefer maximal strength tests. Only leg press repetition tests were correlated with 2000-m ergometer times (e.g. r = -0.67; p < 0.05). However, these tests differentiate training experience and muscle morphology, in that those individuals with greater training experience and/or proportions of slow twitch fibres performed more repetitions. Muscle balance ratios derived from strength data (e.g. hamstring-quadriceps ratio <45% or knee extensor-elbow flexor ratio around 4.2 ± 0.22 to 1) appeared useful in the pathological assessment of low back pain or rib injury history associated with rowing. While strength partially explained variances in 2000-m ergometer performance, concurrent endurance training may be counterproductive to strength development over the shorter term (i.e. <12 weeks). Therefore, prioritization of strength training within the sequence of training units should be considered, particularly over the non-competition phase (e.g. 2-6 sets × 4-12 repetitions, three sessions a week). Maximal strength was sustained when infrequent (e.g. one or two sessions a week) but intense (e.g. 73-79% of maximum) strength training units were scheduled; however, it was unclear whether training adaptations should emphasize maximal strength, endurance or power in order to enhance performance during the competition phase. Additionally, specific on-water strength training practices such as towing ropes had not been reported. Further research should examine the on-water benefits associated with various strength training protocols, in the context of the training phase, weight division, experience and level of rower, if limitations to the reliability and precision of performance data (e.g. 2000-m time or rank) can be controlled. In conclusion, while positive ergometer time-trial benefits of clinical and practical significance were reported with strength training, a lack of statistical significance was noted, primarily due to an absence of quality long-term controlled experimental research designs.

The influence of variable range of motion training on neuromuscular performance and control of external loads

Resistance training programs that emphasize high force production in different regions of the range of motion (ROM) may provide performance benefits. This study examined whether variable ROM (VROM) training, which consists of partial ROM training with countermovements performed in a different phase of the ROM for each set, results in improved functional performance. Twenty-two athletes (age 22.7 ± 2.4 years, height 1.81 ± 0.07 m, and body mass 94.6 ± 14.5 kg) with extensive resistance training backgrounds performed either a VROM or full ROM control (CON) 5-week, concentric work-matched training program. The participants were assigned to a group based on stratified randomization incorporating their strength levels and performance gains in preceding training microcycles. Testing consisted of assessing the force-ROM relationship during isokinetic and isometric bench press and ballistic bench throws, with normalized electromyography amplitude assessed during the isometric tests. Repeated-measure analyses of variance revealed that the VROM intervention significantly (p < 0.05) increased both full ROM bench throw displacement (+15.5%) and half ROM bench throw peak force (+15.7%), in addition to isokinetic peak force in the terminal ROM (13.5% increase). No significant differences were observed in the CON group or between groups for any other outcome measures. Analysis of the force-ROM relationship revealed that that the VROM intervention enhanced performance at shorter muscle lengths. These findings suggest that VROM training improves terminal and midrange performance gains, resulting in the athlete possessing an improved ability to control external loading and produce dynamic force.

Influence of dynamic versus static core exercises on performance in field based fitness tests

Minimal evidence supports the claim that core stability training transfers into improved performance and the most effective training method to perform core exercises is still unknown. The purpose of the study was to compare the effects of a 6 week unstable static versus unstable dynamic core training program, on field based fitness tests. A static (n = 6) and dynamic (n = 6) training group performed two 45 min sessions per week for six weeks. Seven performance tests, consisting of three core (plank; double leg lowering; back extensions), one static (standing stork) and three dynamic (overhead medicine ball throw; vertical jump; 20 m sprint), were administered pre- and post training. Between group differences were assessed using a repeated measures MANOVA (P < 0.05). Both training groups improved in each of the core tests (P < 0.05). Neither training group demonstrated improvement in the dynamic field based tests (medicine ball throw, vertical jump height and 20 m sprint) (P > 0.05). Findings indicate that both types of training improved specific measures of core stability but did not transfer into any sport-related skill.