Isokinetics and Exercise Science

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Fifteen subjects with limited ankle DF were recruited. The subjects performed the three abovementioned methods.

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).

The preferred method to increase ankle DF ROM is GCM stretching combined with talar self-stabilisation and subtalar supination.

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.

To assess the reproducibility and criterion validity of a prototype FW-RE acquisition system.

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.

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%).

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.

Muscle stretch reflexes are widely used to examine neural muscle function. The knowledge of reflex response in muscles crossing the shoulder is limited.

To quantify reflex modulation according to various subject postures and different procedures of muscle pre-activation steering.

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.

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).

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.

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).

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.

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.

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.

There have been multiple studies focusing on the relationship between ankle muscle torque and fatigue with different body positions but have found conflicting results.

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.

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.

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).

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.

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.

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).

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).

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.

Prone standing hip extension with AB at 60 ∘ /s offers an effective option for measuring hip extension strength.

Heart rate variability may reveal sensitive information about the athletes’ physiological adaptation when exercising for sport performance.

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.

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.

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).

HRV at rest may predict results in competition, being a complementary tool for coaches.

The use of force-velocity imbalance (Fvimb) has been proposed as an effective method for prescribing training loads aiming to enhance physical performance.

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.

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).

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.

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.

Many daily functions and sporting events need high activity level of the flexor muscles of the forearms and hands. Handgrip strength is measured by a handheld dynamometer which is a reliable, safe and inexpensive device.

The study aims to find out whether the presence or absence of flexor digitorum superficialis tendon of the fifth (little) fingers (FDS-V) affects handgrip strength of athletes from different types of sports.

The effect of presence or absence of the FDS-V in a total number of 788 fingers of athletes (male n = 200, female n = 194) was assessed using isometric handgrip strength.

No statistically significant difference existed in handgrip strength of the participants with and without the FDS-V of the little finger ( p > 0.025).

The presence or absence of FDS-V of the little finger in athletes has no effect on handgrip strength.

Tissue flossing is a new method aiming to improving range of motion (ROM), pain, and enhancing injury prevention. Tissue flossing involves passive twisting and active movement with the muscle or joint tightly wrapped with a floss band. However, evidence is lacking regarding the effects of flossing.

To compare the effects of flossing and static stretching (SS) on gastrocnemius (GC) function.

Twenty healthy young men received three interventions (Flossing, SS, Rest). The experimental intervention involved flossing using a floss band (Sanctband COMPRE Floss TM Blueberry), and the control intervention involved SS for 5 minutes. The following outcomes were measured before (pre) and after (post) each intervention: dorsiflexion ROM, passive moment, fascicle length, muscle hardness, maximal isometric voluntary plantar flexion contraction, rate of force development (RFD), and muscle activity.

The pre-post changes in RFD 0–50 and RFD 0–100 ms were significantly higher with Flossing compared to SS. The pre-post changes in dorsiflexion ROM was significantly higher with Flossing compared to Rest.

Flossing on GC improved RFD 0–50 and RFD 0–100 ms with an increase in dorsiflexion ROM unlike SS. Research is warranted whether flossing before exercise may be more beneficial than SS for injury prevention and physical performance enhancement.

Although it is known that isokinetic knee extensor strength and balance ability are important, valid and reliable parameters, they have not been used hitherto to predict the performance of junior weightlifters.

To investigate the relationship among body composition, isokinetic knee extensor strength, balance, and weightlifting performance and to determine whether these factors predict competition performance in junior men weightlifters.

Fifty-one male junior weightlifters (age: 15.9 ± 1.2 years, height: 161.9 ± 7.7 cm, body mass: 62.7 ± 11.3 kg) participated in this study. Participants performed isokinetic knee extensor strength tests in concentric mode (at 60 and 180 ∘ /s) and balance tests (static and dynamic). Competition performance was calculated according to the Sinclair equation, which was used as the dependent variable in the statistical analysis. The extent to which the independent variables predicted competition performance was determined by bivariate correlations and multiple linear regression analysis.

Significant correlations were found between the Sinclair score and the independent variables ( r = 0.496–0.804, p < 0.05). Three models were fitted by hierarchical linear regression analysis. Body fat percentage was determined as a control variable in step one, isokinetic knee extensor strength at 180 ∘ /s was included in step two, and static balance was included in step three, with all three contributing to the models significantly ( p = 0.0001, p = 0.0001, and p = 0.003, respectively). The variance of competition performance was explained by approximately 65% in step one, approximately 78% in step two, and approximately 82% in step three.

The results of this study suggest that isokinetic knee extensor strength, static balance, and body fat percentage are effective for predicting competition performance in junior weightlifters.