Isokinetics and Exercise Science - Volume 28, issue 2
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Isokinetics and Exercise Science (IES) is an international journal devoted to the study of theoretical and applied aspects of human muscle performance. Since isokinetic dynamometry constitutes the major tool in this area, the journal takes a particular interest in exploring the considerable potential of this technology.
Isokinetics and Exercise Science publishes studies associated with the methodology of muscle performance especially with respect to the issues of reproducibility and validity of testing, description of normal and pathological mechanical parameters which are derivable from muscle testing, applications in basic research topics such as motor learning paradigms and electromyography. The journal also publishes studies on applications in clinical settings and technical aspects of the various measurement systems employed in human muscle performance research.
Isokinetics and Exercise Science welcomes submissions in the form of research papers, reviews, case studies and technical reports from professionals in the fields of sports medicine, orthopaedic and neurological rehabilitation and exercise physiology.
Abstract: BACKGROUND: While extreme changes in body position (e.g., standing vs. sitting) have been shown to affect knee extensor strength, little is known regarding how less extreme changes in body position affect knee extensor strength and activation. OBJECTIVE: This study evaluated the effect of four seated positions on the maximum voluntary isometric contraction (MVIC) and electrically-evoked isometric strengths of the knee extensors. METHODS: Forty healthy subjects participated. MVIC strength, electrically-evoked strength, and voluntary activation of the quadriceps muscles were measured under four seated positions: 1) 22.5–25 ∘ forward tilt, 2)…0 ∘ tilt, 3) 22.5–25 ∘ backward tilt, and 4) 45–50 ∘ backward tilt. The effect of seated position on each dependent variable was assessed using a one-way repeated measures ANOVA with linear contrasts. RESULTS: MVIC and electrically-evoked strengths increased (P ⩽ 0.037) by 5–11% as the body was moved from the 22.5–25 ∘ forward-tilted to 45–50 ∘ backward-tilted position. However, voluntary muscle activation and EMG amplitudes of the knee extensors during MVIC did not change. CONCLUSIONS: Knee extensor MVIC and electrically-evoked strengths were modestly enhanced as the body was tilted backwards. The use of a semi-reclined position may assist in obtaining a more forceful contraction of the knee extensors, thereby potentially resulting in better strength training outcomes.
Abstract: BACKGROUND: The majority of common agility tests include pre-planned change of direction (COD) maneuvers which require muscular coordination. However, muscular coordination in terms of organization of co-activated antagonistic muscle pairs in COD maneuvers have not been studied. OBJECTIVE: To evaluate muscle coordination by analyzing co-contraction at knee and ankle during three agility tests and to investigate the relationships between muscle coordination and test completion time. METHOD: Thirteen healthy young male subjects (22.1 ± 1.9 years) participated in the study. Surface EMG and acceleration signals were used to calculate co-contraction index…(CCI) for selected antagonistic muscle pairs of ankle and knee joints during COD maneuvers in agility tests. RESULTS: The findings indicated that concurrent activation costs a delay to complete the test faster. CCI was higher at right ankle and left knee and showed an increasing trend with advancing the phase when the test requires multiple CODs. CONCLUSIONS: Minimizing co-contraction would result in faster movement, however, there might be a trade-off between joint stiffness and test performance depending on changes in neuromuscular factors such as altered motor control strategies due to strength imbalances or occurrence of fatigue.
Abstract: BACKGROUND: Exercises that stretch the gastrocnemius (GCM) lead to greater ankle dorsiflexion (DF). GCM stretching combined with talar self-stabilisation has been reported to increase ankle DF range of motion (ROM). However, excessive subtalar and midtarsal pronation during GCM stretching may compensate for reduced ankle DF. Thus, this study examined the combined immediate effect of stretching GCM and stabilising talus and subtalar supination on limited ankle DF. OBJECTIVE: This study aimed to investigate the immediate effect of GCM stretching alone, GCM stretching with talar self-stabilisation and GCM stretching with talar self-stabilisation and subtalar supination on ankle kinematics…in subjects with limited ankle DF. METHODS: Fifteen subjects with limited ankle DF were recruited. The subjects performed the three abovementioned methods. RESULTS: GCM stretching with talar self-stabilisation and subtalar supination significantly increased open-chain and closed-ankle DF ROM compared with GCM stretching alone. Moreover, GCM stretching combined with talar self-stabilisation and subtalar supination significantly increased open-chain ankle DF ROM with knee straight compared with pre-intervention (P < 0.017). CONCLUSIONS: The preferred method to increase ankle DF ROM is GCM stretching combined with talar self-stabilisation and subtalar supination.
Abstract: BACKGROUND: Flywheel (FW) load represents a new trend among resistance exercise (RE) modalities; however, protocols and acquisition systems to measure FW-RE parameters are not yet fully researched and developed. OBJECTIVE: To assess the reproducibility and criterion validity of a prototype FW-RE acquisition system. METHODS: Thirty-eight student volunteers completed the low-row FW testings with a test-retest break of 1 week. Force (F), power (P) and velocity (v ) parameters were simultaneously collected using a prototype FW acquisition system and a load cell (LC), respectively. Paired samples t -test was used…to determine differences between test-retest and inter-devices results. The analysis included Pearson’s correlation (r ), standard error of measurement (SEM), smallest real difference (SRD) and Bland-Altman plots. In addition, for reproducibility purposes, ICC and smallest real difference (SRD) were calculated. RESULTS: An excellent correlation was found between FW and LC parameters (r = 0.971–0.997). The FW acquisition system provided us with significantly higher values among F and P parameters for men and women. The testing protocol that was used has shown good-to-excellent reproducibility for FW acquisition system in men (ICC = 0.771–0.985) and women (ICC = 0.773–948), respectively. Both men and women performed better during the retest. SEM and SRD values were higher for women (4.4–22.7%) compared to men (4.9–10.5%). CONCLUSIONS: The FW device and acquisition system described in this study has shown adequate criterion validity and good-to-excellent reproducibility of mechanical RE parameters for sports-diagnostic purposes. However, a familiarization session is necessary to obtain true measurements of a performance when using the FW based assessement in women.
Abstract: BACKGROUND: Muscle stretch reflexes are widely used to examine neural muscle function. The knowledge of reflex response in muscles crossing the shoulder is limited. OBJECTIVE: To quantify reflex modulation according to various subject postures and different procedures of muscle pre-activation steering. METHODS: Thirteen healthy male participants performed two sets of external shoulder rotation stretches in various positions and with different procedures of muscle pre-activation steering on an isokinetic dynamometer over a range of two different pre-activation levels. All stretches were applied with a dynamometer acceleration of 10 4 ∘…/s 2 and a velocity of 150 ∘ /s. Electromyographical response was measured via sEMG. RESULTS: Consistent reflexive response was observed in all tested muscles in all experimental conditions. The reflex elicitation rate revealed a significant muscle main effect (F (5,288) = 2.358, ρ = 0.040; η 2 = 0.039; f = 0.637) and a significant test condition main effect (F (1,288) = 5.884, ρ = 0.016; η 2 = 0.020; f = 0.143). Reflex latency revealed a significant muscle pre-activation level main effect (F (1,274) = 5.008, ρ = 0.026; η 2 = 0.018; f = 0.469). CONCLUSION: Muscular reflexive response was more consistent in the primary internal rotators of the shoulder. Supine posture in combination with visual feedback of muscle pre-activation level enhanced the reflex elicitation rate.
Abstract: OBJECTIVE: The main purpose of this study is to investigate the effects of lumbar stabilization exercises on pain intensity, transversus abdominis (TrA) activation capacity, functional disability, and TrA thickness in patients with low back pain (LBP). METHODS: The subjects of this study were 30 LBP patients. The experimental group performed diverse lumbar stabilization exercises (LSE) in different postures, and the control group conducted an ordinary trunk muscle strengthening exercise (TSE). All interventions were conducted 3 times per week for 6 weeks. RESULTS: Significant differences between LSE and TSE groups were shown in the…pain intensity, TrA activation capacity, and functional disability after the intervention (p < 0.05). However, there were no significant differences between LSE and TSE groups in TrA thickness. CONCLUSION: This study provides clinical evidence that LSE for LBP patients is more effective than TSE in improving pain intensity, functional disability, and TrA activation capacity.
Keywords: Low back pain, lumbar stabilization exercise, transverse abdominis
Abstract: BACKGROUND: There have been multiple studies focusing on the relationship between ankle muscle torque and fatigue with different body positions but have found conflicting results. OBJECTIVE: We investigated the effect of body position on maximum voluntary isometric contractions (MVIC) of ankle plantarflexors (PF) and dorsiflexors (DF) in the pre and post-fatigued conditions in healthy adults. METHODS: Twenty-five participants ran on a treadmill until volitional exhaustion by performing the Bruce protocol. The participants then performed three MVICs for both PF and DF before and after volitional exhaustion. RESULTS: Peak torques of…PF (p < 0.01) and DF (p < 0.01) in the pre-fatigue condition were greater than in the post-fatigue condition regardless of the body position. Peak torques of PF (p < 0.01) and DF (p = 0.03) in the seated position were greater than in the supine position regardless of time. Variances of peak torque differences were not significantly different between the pre and post-fatigue conditions for the seated and supine positions (p = 0.09). CONCLUSIONS: The results of this study suggest that the body position affects ankle PF and DF torques but does not influence the magnitude of PF and DF strength declines elicited by a fatiguing protocol. Therefore, to obtain the most reliable MVIC measurements, the body position during MVICs should be consistent.
Keywords: Running, Bruce protocol, fatigue, maximum voluntary isometric contraction (MVIC), isokinetic dynamometer
Abstract: BACKGROUND: Abdominal stabilization is an important factor during hip extension. Additionally, the prone standing position is a more effective and functional position for hip extension than the prone or supine positions. OBJECTIVE: To determine the concentric isokinetic strength of the hip extensors during prone standing hip extension (PSHE) using stabilization maneuvers such as abdominal resting (AR), abdominal bracing (AB), and abdominal hollowing (AH). METHODS: Thirty one healthy subjects were recruited for this study. In each of the 3 maneuvers the participants performed concentric isokinetic hip extensions, 4 at 60 ∘…/s and 5 at 180 ∘ /s. The outcome variables consisted of the peak moment (PM), total work (TW), and average power (AP). RESULTS: Hip extension strength, as indicated by the PM, differed significantly among the three conditions at both velocities (p < 0.05). Significantly greater strength was achieved with AB than with AH at 60 ∘ /s, but no such differences were evident at 180 ∘ /s. CONCLUSIONS: Prone standing hip extension with AB at 60 ∘ /s offers an effective option for measuring hip extension strength.
Keywords: Abdominal bracing, abdominal hollowing, hip extension, prone standing position
Abstract: BACKGROUND: Heart rate variability may reveal sensitive information about the athletes’ physiological adaptation when exercising for sport performance. OBJECTIVE: The aim of this study was to demonstrate whether heart rate variability (HRV) measurements were able to predict sport results and determine which type of measurements, at rest or during routines, were relevant in anticipating the performance. METHOD: Ten female gymnasts, aged 11–14 years old, and 16 age-matched non-active adolescents participated in this study. HRV was measured at rest for 10 minutes and throughout the training routines one week prior to competition. Correlations and…multivariate analysis determined the parameters predicting performance. Significance was set at p ⩽ 0.05. Results: At rest, the gymnasts displayed higher HRV values than controls. At rest, sympathetic parameters correlated with sport results whereas no correlation was observed during routines. The magnitude of the predictive factors highlighted the importance of Ln SD2 (coefficient = - 117, 95CI - 130 to - 106), Ln RMSSD (coefficient = - 24.5, 95CI - 29.2 to - 19.8), Ln pNN50 (coefficient = - 10.7, 95CI - 11.5 to - 9.9), and Ln Total power (coefficient = - 2.5, 95CI - 13.4 to - 11.5). CONCLUSIONS: HRV at rest may predict results in competition, being a complementary tool for coaches.
Abstract: BACKGROUND: The use of force-velocity imbalance (Fvimb) has been proposed as an effective method for prescribing training loads aiming to enhance physical performance. OBJECTIVE: This study aimed to analyse the effects on lower body strength, jump and sprint performance of different individualised resistance training (RT) programmes based on Fvimb in rugby players. METHODS: Thirty-four senior rugby players were divided into four groups according to their Fvimb: Not individualised (NI, n = 8), velocity imbalance (Vimb, n = 6), force imbalance (Fimb, n =…11) and well balanced (WB, n = 9). The intervention period consisted of a 7-week resistance, plyometric and sprint training programme performed twice a week. Pre- and Post-training measures included Force-velocity (Fv) profile, countermovement jump (CMJ), 30 m sprint test and estimated one-repetition maximum in squat (1RM-SQ). RESULTS: Significant “group” × “time” interactions (P < 0.05) were observed for theoretical maximal velocity (V0), theoretical maximal force (F0), and Fvimb. No significant “group” × “time” interactions were observed for the rest of variables analysed. The Vimb group significantly (P < 0.05) increased V0, whereas decreased F0 and Fvimb. The Fimb group showed significant (P < 0.05) decreases in V0, whereas increased F0 and Fvimb. The WB and NI groups did not show significant changes in these parameters. The WB group induced significant enhancements in 10 m, 20 m, and 30 m sprint times, maximum sprint speed and sprint momentum (SM), whereas Fimb attained significant changes in 20 m and 30 m sprint times. The NI group attained significant improvements (P < 0.05) in SM. No significant changes were observed for 1RM-SQ and jump performance. CONCLUSION: Individualised RT programs based on Fvimb induced improvements in sprint performance. Moreover, individualised RT programs based on Fvimb induced better adjustments of the Fv profile to the theoretical “optimal” Fv profile, although any group improved SQ strength, jump height or maximum power.