Relationship between kinetic variables of isometric knee extension test with vertical jump test

The use of torque variability and slope measures to detect submaximal efforts has been studied in isometric tests, but not fully investigated in isokinetic tests. The purpose of this study was to investigate differences between maximal and submaximal efforts in isometric and isokinetic knee extension using torque variability and slope measures obtained from 32 volunteers (age = 25.2 +/- 4.7 years). The coefficient of variation of average torque, coefficient of variation of peak torque, and slope to peak torque were obtained from maximal and submaximal torque curves during isometric and two isokinetic tests (60 degrees/sec and 180 degrees/sec). Significant differences between effort levels (maximal and submaximal) were shown for all variables in isometric and isokinetic tests. An optimized cut-off value to determine submaximal efforts without false positives was determined for each variable. The coefficient of variation of average torque detected 75% of submaximal efforts at 180 degrees/sec and slope to peak torque detected 63% of submaximal efforts at 60 degrees/sec. For both speeds, combining the coefficient of variation of average torque with slope improved the submaximal detection rate to 84%. No variable provided a satisfactory detection rate for the isometric test. Therefore, submaximal isokinetic knee extensions are detectable with torque variability and slope measures, but submaximal isometric exercise is not detectable.

Several studies have shown that force application is influenced by different neuromuscular mechanisms depending on the time of force application analysis in isometric knee extension test (IKE), and a countermovement jump (CMJ) has contributions from knee extension, so some CMJ variables could be indicators of such mechanisms. Purpose: The aim of this study was to determine the level of relationship of variables of IKE and bilateral CMJ tests. Methods: Male college soccer players (n = 25; corporal mass = 72 ± 8 kg; height = 171 ± 5 cm; age = 22 ± 2 years) performed the IKE at two angles (60° and 75°) on an isokinetic machine and the CMJ on two uniaxial force platforms. To determine the level of relationship, Pearson's correlation coefficient was analyzed between the test variables. Results: Trivial to moderate correlations (r = -0.45 to 0.62; p < 0.05) were found between CMJ variables and IKE in both knee angles (60° and 75°); Conclusions: The variables of IKE have a trivial to moderate correlation with the variables of CMJ, so the variables of CMJ could not be considered interchangeably with those of IKE and therefore considered indicators of neuromuscular mechanisms isolated from the knee extensor function. Longitudinal design (fatigue or training protocols) should be realized to corroborate these results.

This study aimed to examine the sensitivity of the isometric knee extension (IKE) test to detect changes in the lower-limb strength of institutionalized older adults after exercise and inactivity periods. Thirty-four and fifteen institutionalized older adults completed the training and inactive periods, respectively. At each time point, the participants completed two testing sessions. In the first session, they performed the IKE test. As a complement to this evaluation, the second testing session was used to assess their functional capacity and handgrip strength. The sensitivity of the IKE test was examined by comparing the changes generated in this test against the repeatability of the protocol. A 4-week multicomponent Vivifrail program was implemented. After that, a subsample of the participants was re-evaluated after a 14-week inactivity period. Significant changes (p &lt; 0.01; ES ≥ 0.27) in the IKE strength for both the dominant (+0.27 N/kg) and non-dominant legs (+0.25 N/kg) were produced after the training intervention. Likewise, significant decrements (p &lt; 0.01; ES ≥ 0.31) were detected after the inactive period for the dominant (−0.29 N/kg) and non-dominant legs (−0.32 N/kg). All mean changes were found to be superior to the variability threshold of the IKE test for both legs, with superior sensitivity for the non-dominant leg (≥73%). Thus, the IKE test is a sensitive and practical tool for detecting changes in the lower-limb strength of institutionalized older adults after exercise and inactivity periods. Because of its applicability, it seems pertinent to implement the IKE test in a geriatric context.

Marshall et al. (2011) recently published the results of a comprehensive strength training study investigating the effect of the number of sets used in each training session on muscle function, hypertrophy and activation [assessed by electromyography (EMG)] in men with previous weight training experience [mean squat lift load = 159.9 kg (1.9 9 body mass)]. Squat lift training was performed at 80% of 1 RM to exhaustion twice weekly for 6 weeks, then a combination of heavier (4–12 RM) and lighter, explosive (e.g. jump squat) exercises were performed for 4 weeks. The results were very interesting, revealing that the performance of eight sets of exercises was superior to one and four sets for muscle strength improvement in their cohort. One intriguing result was that the rate of force development (RFD), measured during an isometric knee extension test, did not improve with training despite there being a small increase in the rate of muscle activation (measured as the rate of integrated EMG increase) in addition to the substantial (11.7–22.8%) increase in strength. On their own, each of these adaptations could have been expected to result in an increase in RFD (Aagaard et al. 2002). From this, it could be concluded that the preponderance of slowspeed dynamic exercises was not appropriate to improve RFD, or that the use of an isometric test was inappropriate. These opinions make sense given our understanding of the specificity of adaptations to strength training. However, the question should be asked: does the published research support these assertions? Numerous studies have reported significant enhancements in RFD measured in the isometric knee extension test after traditional, explosive or isometric strength training of the lower extremity (e.g. Aagaard et al. 2002; Blazevich et al. 2009; Blazevich et al. 2008; Del Balso and Cafarelli 2007; Hakkinen et al. 2003; Hakkinen et al. 2001a, b; Narici et al. 1996; Reeves et al. 2003; Suetta et al. 2004; Vila-Cha et al. 2010). In each of these studies, some portion of test-specific training was performed as part of the program. That is, the knee extension training was performed in training, so there was at least some similarity (specificity) between the testing and training tasks with respect to body position. The same result is seen when training is done in other muscle groups, including the trapezius (Andersen et al. 2009), elbow flexors (Barry et al. 2005; Gabriel et al. 2001), plantarflexors (Holtermann et al. 2007) and dorsiflexors (Geertsen et al. 2008), or when a multi-joint isometric leg press test is used to assess RFD after a period of dynamic leg press training (Hoff et al. 2007; Husby et al. 2009; Mosti et al. 2011; Wang et al. 2010). Of the studies cited here, the mean improvement in absolute RFD was 42.6% (mean of all published results), which, when the results are expressed as the sample size-weighted mean, equates to a 4.4% increase per week. Interestingly, there appears to be no clear evidence that there is a requirement for fast force production during the training, with increases of only 8.0% at 0.4% per week when some form of explosive training was performed compared to 31.3% at 1.3% per week when slower strength training was performed. In fact, the evidence more clearly supports the reverse hypothesis, and it is rarely seen that strength training is not associated with an increase in RFD measured isometrically (Hakkinen et al. 1998; Sleivert et al. 1995). Thus, the overwhelming Communicated by Susan A. Ward.

The purpose of this study was to quantify the rate of force development (RFD) and maximum force in isometric, concentric, and stretch-shorten cycle contraction modes and to determine their relationships to sprint running performance. Fifteen athletic subjects performed a series of isometric, concentric, and stretch-shorten cycle RFD tests in an upright squat position using a modified Smith machine positioned over a force platform. The concentric and isometric tests were performed at both 110° and 150° knee angles. From the force data recorded, the maximum force, maximum RFD, force at 30 ms, and impulse at 100 ms were used as test variables. Subjects also ran a 30-m indoor sprint from a crouched start. Of the 20 force-time variables calculated, the concentric tests were the only ones significantly correlated to performance and able to effectively discriminate between good and poor performers. Isometric tests were unrelated to dynamic performance. This was suggested to be due to the large neural and mechanical differences between isometric and dynamic muscular actions. The results are strongly supportive of the use of concentric RFD tests but not isometric ones.

This study evaluated the reliability and sensitivity of a set of different common strength and power tests in a healthy adult population in a span of 9 weeks. Seventeen subjects (24.2 ± 2.2 years, 1.75 ± 0.10 m, 68.6 ± 14.2 kg, seven women) participated in the study. We tested countermovement jumps, reactive hops, and the maximal voluntary contraction (MVC) of handgrip and isometric knee extension. The tests were conducted in three separate sessions across a nine-week period, with one week between the first two sessions and eight weeks between the second and the third. Reliability and sensitivity statistics for each test were calculated for both the average of three trials and the best result during each session. The MVC of isometric knee extension and handgrip, as well as the countermovement jump test, demonstrated very high reliability and sensitivity over the nine-week period. The peak force of the reactive hops demonstrated high reliability but high sensitivity only for the average but not for the best result. The average contact time of reactive hops was neither a sensitive nor reliable measurement. In conclusion, isometric maximal knee extension and handgrip tests, as well as countermovement jumps and peak force of reactive hops, can be used as reliable and sensitive measurements of isometric and reactive strength and power over time periods of up to eight weeks. We recommend the use of the average results of three trials instead of the best performance value for longitudinal studies, as this procedure produces more consistent results and a lower measurement error.

Eight moderately active male subjects where tested for peak force in an isometric knee extension test and peak force and rate of force development in an isometric squat test. Both tests where performed at a 100 degrees knee angle and average integrated electromyography (IEMG) was measured from the vastus medialis (VM), vastus lateralis (VL) and biceps femoris (BF) muscles. Subjects performed the two conditions, stretching (S) or control (C) in a randomized order. Subjects where tested for baseline strength measures in both the isometric knee extension and isometric squat and then either stretched or sat quietly for 10 min. Following S or C subjects where then tested at six time points. Following S peak force in the isometric knee extension was significantly (P < or = 0.05) less than C at 1, 2, 8 and 16 min post. No significant difference in peak force was found between S and C in the isometric squat. However, following S the rate of force development in the isometric squat was significantly less than C at immediately post. No significant differences where observed in IEMG of the VM or VL between S and C in either the isometric knee extension or isometric squat. However, IEMG significantly decreased in the BF at 1 min post after S in comparison with C in both the isometric knee extension and isometric squat. Stretching appears to decrease muscle force output in a single joint isometric contraction and rate of force development in a multiple joint isometric contraction. Possible changes in agonist-antagonist muscle activity patterns need to be further examined.

Introduction: Individuals affected with ryanodine receptor isoform-1-related myopathies (RYR1-RM) commonly experience fatigability in the quadriceps, which may limit physical function and potentially diminish quality of life. Fatigability, in RYR1-RM, results from skeletal muscle injury secondary to dysfunction of the major skeletal muscle Ca++ channel. However, during fatigability testing, affected individuals did not always reach the point of local muscle fatigue as defined by a fatigue index (FATI) at 50% of peak torque. Surakka et al. compared three versions of FATI equations, which vary by the area under the force curve (AUC). By performing this comparison, they were able to determine the optimal equation in individuals with Multiple Sclerosis.Purpose: Using a similar comparison, we sought to identify the optimal FATI equation in the RYR1-RM population. Secondly, because local muscle fatigability might have an impact on independent living, this study also assessed change in local muscle fatigability over a 6-month time frame.Methods: Thirty participants were analyzed from the RYR1-RM natural history study and double-blind, placebo-controlled N-acetylcysteine (NAC) trial, NCT02362425. Twenty-seven had fatigability data, from isometric knee extension and flexion fatigability tests, available for the purpose of establishing a method for predicting FATI at 50% peak torque. For the natural history study, 30 participants were used to assess disease progression of local muscle fatigability achieved during the knee extension fatigability test, and 29 participants for the knee flexion fatigability test.Results: Surakka's equation 1, using the prediction approach, led to the smallest median error, the smallest square-root of uncorrected sum of squares, and the smallest average of the absolute value of the differences. No difference was observed in FATI at 50% peak torque between month 0 and month 6 for extension (p = 0.606) and flexion (p = 0.740).Conclusion: Surakka's equation 1, with the prediction approach, was found to be the most accurate for imputing values when fatigue was not reached during a sustained knee isometric fatigability test in RYR1-RM. Furthermore, when used to assess fatigability-based disease stability, local muscle fatigability, in this RYR1-RM population remained stable.

Quantification of full-range-of-motion unilateral and bilateral knee flexion and extension torque ratios

Background:The standard of care in ACL reconstruction (ACLR) typically involves standardized strength testing at 6 months or later to assess a patient’s readiness to return to play (RTP) using isokinetic and isometric testing, and functional strength testing. Recent literature suggests that isokinetic knee extension strength should demonstrate 89% limb symmetry index (LSI) or greater prior to returning to sport. However, there is little known on the effects of strength testing early in the rehabilitation process and the relationship to strength test performance at time of RTP.Purpose:The purpose of this study was to examine how early post-operative strength test performance impacts isokinetic strength outcomes at RTP testing in adolescents.Methods:The retrospective cohort study included patients undergoing primary ACLR between 12 and 18 years of age, early post-operative strength measures, and isokinetic dynamometer strength at RTP from July 2017 and April 2019. Data was dichotomized into desired outcomes at 3 months: >70% isometric knee extension LSI, > 20 repetitions on anterior stepdown test (AST), > 90% LSI Y Balance. At RTP testing, isokinetic knee extension strength data was categorized into >89% LSI at 3 speeds (300, 180, 60°/sec). Chi square testing and odds ratio statistics were used to examine association and its magnitude.Results:63 patients met inclusion criteria (38 females; 15.37±1.66 years old). >70% LSI isometric knee extension strength at 3 months showed a significant association (Table 2) and demonstrated the strongest odds of having >89% LSI on isokinetic strength tests at all 3 speeds at RTP with 180°/sec being the highest (OR=14.5; 95% CI=4.25,49.43; p= <0.001). Performance on AST showed a significant association (χ2 (1, n=63) = 17.00, p <0.001), and highest odds at 180°/sec (OR=4.61; 95% CI = 1.59, 13.39, p=<0.001) and 60°/sec (OR= 3.07; 95% CI = 1.10, 8.63, p= 0.04). Combination of performance on isometric strength tests and AST showed a significant association to isokinetic strength at all three speeds, but less predictive then isometrics in isolation. (Table 2). There was no significant relationship between YBR LSI at 3 months and isokinetic strength at 6 months.Conclusion:Standardized strength testing early in rehabilitation can help identify patients that will successfully complete RTP testing. Our results suggest that isometric knee extension strength and timed anterior stepdown test provide meaningful clinical information early in the rehabilitation process. This data also suggests that the use of YBAL for predicting isokinetic strength performance is limited.

Context : Clinicians assessing limb symmetry after ACL reconstruction (ACLR) use various tools including functional tests (eg, countermovement jump [CMJ]) and isolated strength tests (eg, isometric isokinetic dynamometry). However, it is unclear how these different assessment modalities and calculation methods compare, which may have significant implications for clinical decision making when interpreting asymmetry. Design : A repeated-measures, cross-sectional observational study. Methods : Fourteen participants post-ACLR (phase 3 rehabilitation) and 25 healthy controls were assessed. Participants completed unilateral isometric knee extension testing on an isokinetic dynamometer and bilateral CMJ testing on a dual force plate system. Asymmetry was calculated using 5 different equations. Results : A within-group analysis showed that participants post-ACLR had significantly different asymmetry magnitudes when comparing the CMJ and isometric tests (mean difference = 5.64%–12.45%, P &lt; .006). Healthy controls showed no difference in asymmetry between the 2 tests ( P &gt; .617). A between-group analysis showed that the ACLR group was significantly more asymmetric than controls on both the CMJ test (mean difference = 7.95%–22.12%, P &lt; .001) and the isometric test (mean difference = 14.02%–36.24%, P &lt; .001). However, both testing methods exhibited adequate sensitivity (0.79) and specificity (0.99) for differentiating those with ACLR from healthy controls. Conclusion : Asymmetry values are highly dependent on the assessment modality (functional jump vs isolated strength). While participants post-ACLR were more asymmetric than healthy controls on both tests, the magnitude of their asymmetry differed significantly between the 2 tests. This finding indicates that asymmetry values from functional and isolated tests are not interchangeable and underscores the need for test-specific interpretation in clinical practice.

Isometric knee extension test: A practical, repeatable, and suitable tool for lower-limb screening among institutionalized older adults.

Despite the rising interest in the use of portable force sensors during isometric exercises to inform on neuromuscular performance, the design of practical field-based methods to obtain reliable measures is an ongoing challenge. We aim at identifying the intra-session and test-retest reliability of a rapid, isometric knee extension test to evaluate the maximal voluntary concentric force (MVC), rate of force development (RFD) and impulse following a field-based approach. On two occasions, 14 athletes unfamiliar with the test completed three sets of 2 s ballistic contractions (as fast and hard as possible) with 30 s rest. Raw and filtered data were collected in real time using a portable force sensor. RFD and impulse were highly reliability during “late” phases of the contraction (0–250 ms) since the first session (coefficient of variation (CV) &lt; 9.8%). Earlier phases (0–150 ms) achieved a moderate reliability after one familiarization session (CV &lt; 7.1%). Measures at 0–50 ms did not reach sufficient reliability (CV~14%). MVC was accurately assessed. Dominant limbs were not importantly altered by the familiarization. In opposite, non-dominant limbs showed large variations. New evidence is provided about the positive effects of a single familiarization session to improve the reliability the isometric knee extension test for rapid force production assessment. Coaches and practitioners may benefit of from these findings to conduct practical and reliable assessments of the rapid force production using a portable force sensor and a field-based approach.

Isometric tests to evaluate upper and lower extremity functioning in people with multiple sclerosis: reliability and validity

To date, little research has been conducted to test the efficacy of different forms of motivation based on a female child's personality type. The purpose of this study was to evaluate the ability of female children to perform a maximal knee extension isometric torque test with varying forms of motivation, based on the child's personality type (introvert vs. extrovert). The subjects were asked to perform a maximal isometric knee extension test under three different conditions: 1) with no verbal motivation, 2) with verbal motivation from the evaluator only, and 3) with verbal motivation from a group of their peers and the evaluator combined. A 2×3 mixed ANOVA was significant for an interaction (F 2,62=17.530; p<0.0005). Post hoc testing for the introverted group showed that scores without verbal motivation were significantly higher than with verbal motivation from the evaluator or the evaluator plus the peers. The extroverted group revealed that scores with verbal motivation from the evaluator or the evaluator plus the peers were significantly higher than without verbal motivation. Results suggest that verbal motivation has a varying effect on isometric knee extension torque production in female children with different personality types. Extroverted girls perform better with motivation, whereas introverted girls perform better without motivation from others.