Bilateral deficit in explosive force production is not caused by changes in agonist neural drive

Unilateral and Bilateral Isokinetic Leg Extensions Exhibit No Differences in Neuromuscular Excitation Under Maximal and Fatiguing Conditions

Anders, JPV, Neltner, TJ, Smith, RW, Arnett, JE, Housh, TJ, Schmidt, RJ, and Johnson, GO. Unilateral and bilateral isokinetic leg extensions exhibit no differences in neuromuscular activation under maximal and fatiguing conditions. J Strength Cond Res 38(3): 474–480, 2024—The bilateral deficit is a phenomenon where force production during a bilateral (BL) muscle action is less than the sum of force produced when the muscle action is performed unilaterally (UL) with both limbs. The purpose of this study was to compare peak force, electromyographic (EMG) amplitude (AMP), and mean power frequency (MPF) of the nondominant leg between UL and BL isokinetic leg extensions. Eleven recreationally trained men (mean ± SD; age = 20.8 ± 1.7 years; body mass = 84.0 ± 16.2 kg; height = 179.3 ± 7.2 cm) volunteered to participate in this study. The 2 test visits included UL and BL maximal isokinetic leg extensions at 180°·second−1 followed by a fatiguing task of either 50 UL or 25 UL followed immediately by 25 BL (ULBL) maximal, isokinetic leg extensions at 180°·second−1, in random order on separate days. The results demonstrated a significant (p = 0.015, = 0.460) bilateral deficit in force (UL = 56.29 ± 11.20 kg; BL = 50.32 ± 7.35 kg; d = 0.63; 95% CI [1.42, 10.52]) but no significant bilateral deficit in EMG AMP (p = 0.892, = 0.002). The peak force during the fatiguing task demonstrated a significant main effect for repetition (p < 0.001, = 0.943) characterized by a reduced peak force from repetitions 20–50. Similarly, EMG MPF demonstrated a significant main effect for repetition (p < 0.001, = 0.702) characterized by a reduced EMG MPF from repetitions 35–50. There were no significant effects (p = 0.102–0.387, = 0.096–0.203) for EMG AMP. These findings suggested that the bilateral deficit was not associated with a neuromuscular deficit and UL muscle actions may be used to potentiate force production of subsequent BL muscle actions.

Association of multi-phase rates of force development during an isometric leg press with vertical jump performances

PURPOSE

This study aimed to elucidate characteristics of explosive force-production capabilities represented by multi-phase rate of force developments (IRFDs) during isometric single-leg press (ISLP) through investigating relationships with countermovement (CMJ) and rebound continuous jump (RJ) performances.

METHODS

Two-hundred-and-thirty male athletes performed ISLP, CMJ with an arm swing (CMJAS), and RJ with an arm swing (RJAS). IRFDs were measured during ISLP using a custom-built dynamometer, while CMJAS and RJAS were measured on force platforms. The IRFDs were obtained as rates of increase in force across 50 ms in the interval from the onset to 250 ms. Jump height (JH) was obtained from CMJAS, while RJAS provided JH, contact time (CT), and reactive strength index (RSI) values.

RESULTS

All IRFDs were correlated with CMJAS-JH (ρ = 0.20-0.45, p ≤ 0.003), RJAS-JH (ρ = 0.22-0.46, p ≤ 0.001), RJAS-RSI (ρ = 0.29-0.48, p < 0.001) and RJAS-CT (ρ = -0.29 to -0.25, p ≤ 0.025). When an influence of peak force was considered using partial rank correlation analysis, IRFDs during onset to 150 ms were correlated with CMJAS-JH (ρxy/z = 0.19-0.36, p ≤ 0.004), IRFDs during onset to 100 ms were correlated with RJAS-JH and RJAS-RSI (ρxy/z = 0.33-0.36, p < 0.001), and IRFD during onset to 50 ms was only correlated with RJAS-CT (ρxy/z = -0.23, p < 0.001).

CONCLUSION

The early phase (onset to 150 ms) IRFDs measured using ISLP enabled the assessment of multiple aspects of leg-extension strength characteristics that differ from maximal strength; these insights might be useful in the assessment of the athletes' leg-extension strength capabilities.

Bilateral deficit magnitude increases with velocity during a half-squat exercise

Movement velocity has been viewed as one of the bilateral deficit (BLD) determinants. This research tested the velocity effect on BLD during a half-squat exercise. The role of muscle excitation in BLD was also assessed. BLD amplitude was assessed in 12 male soccer players while performing a half-squat exercise with incremental load. During the exercise's pushing phase, the average force and velocity were measured in bilateral and unilateral conditions to provide the bilateral index (BI) at each interpolated velocity. The vastus lateralis and medialis excitation was assessed during the exercise by calculating the surface electromyography signal root mean square (sEMG_RMS). The BI for sEMG_RMS (sEMG BI) was calculated. The theoretical maximum force (F₀) and velocity (v₀) were also determined. F₀ was +43 (28)% in bilateral compared with unilateral conditions (p < 0.001), whereas v₀ was similar in both conditions (p = 0.386). The BI magnitude rose with the increase in velocity from -34 (7)% at 50%v₀ to -70 (17)% at 90%v₀ (p 0.03-<0.001), whereas no sEMG BI occurred (p: 0.07-0.991 in both muscles). The study reported velocity-dependent changes in the BLD amplitude, with the largest BLD amplitudes occurring at the highest velocities. This behaviour could provide useful information for setting specific contraction velocities to exploit/limit the BLD amplitude as a possible training stimulus.

The Bilateral Deficit Phenomenon in Elbow Flexion: Explanations for Its Inconsistent Occurrence and Detection

The underlying mechanism(s) of the Bilateral Deficit (BLD) phenomenon is without consensus. Methodological inconsistencies across prior works may be an important source of equivocal results and interpretations. Based on repeatability problems with the BLD measure and maximal force definition, the presence or absence of the BLD phenomenon is altered, shifting conclusions of its mechanistic cause. Our purpose in this study was to examine methodological inconsistencies in applying the BLD measure to establish optimal methods for evaluating the underlying mechanism. Eleven healthy participants engaged in one familiarity and five test sessions, completing bilateral and unilateral elbow maximal voluntary isometric contractions. We defined maximal force by averaged and absolute peak and plateau values. BLD was evident if the bilateral index (BI), the ratio of the bilateral over summed unilateral forces, was statistically different from zero. We addressed interclass correlations (ICC), Chronbach's α, standard error of the mean, and minimal detectable change between and within sessions for all force measures and BI. We evaluated all combinations of sessions (i.e., 1-2, 3-5, 5-6) and maximal forces to establish the optimal number of sessions to achieve reliability. BLD was present for test sessions, but not for familiarization. All measures of maximal force were highly reliable between and within sessions (ICC(2,1) ≥ .895). BI was only considered significantly reliable in sessions 3-5 (p < .027), defined by absolute and average plateau forces, but reliability was still quantifiably poor (absolute: ICC(2,1) = .392; average: ICC(2,1) = .375). These results demonstrate that high force reliability within and between sessions does not translate to stable and reliable BI, potentially exposing the lack of any defined BLD mechanism.

Bilateral Deficit During Jumping Tasks: Relationship With Speed and Change of Direction Speed Performance

ABSTRACT

Bishop, C, Berney, J, Lake, J, Loturco, I, Blagrove, R, Turner, A, and Read, P. Bilateral deficit during jumping tasks: relationship with speed and change of direction speed performance. J Strength Cond Res 35(7): 1833-1840, 2021-Research to date has investigated the phenomenon of the bilateral deficit (BLD); however, limited research exists on its association with measures of athletic performance. The purpose of this study was to investigate the magnitude of the BLD and examine its relationship with linear speed and change of direction speed (CODS) performance. Eighteen physically active and healthy university students performed double- and single-leg countermovement jumps (CMJs), drop jumps (DJs), and standing broad jumps (SBJs) to calculate the BLD across jump tasks. Subjects also performed 10- and 30-m sprints and a 505 CODS test, which were correlated with all BLD metrics. Results showed varying levels of BLD across CMJ metrics (jump height, peak force, eccentric impulse, concentric impulse, and peak power), DJ metrics (ground contact time and flight time), and the SBJ (distance). However, a bilateral facilitation was shown for jump height and reactive strength index during the DJ test. The main findings of this study were that: (a) a larger BLD in CMJ height related to a faster 505 COD (left leg) (r = -0.48; p = 0.04), 505 COD (right leg) (r = -0.53; p = 0.02), and COD deficit (right leg) (r = -0.59; p = 0.01), (b) a larger BLD in CMJ concentric impulse related to faster 505 COD (left leg) (r = -0.51; p = 0.03), 505 COD (right leg) (r = -0.64, p = 0.01), and COD deficit (right leg) (r = -0.60; p = 0.01), and (c) a larger BLD in DJ flight time related to a faster 505 COD (left leg) (r = -0.48; p = 0.04). These results suggest that a larger BLD is associated with faster CODS performance, but not linear speed. This highlights the individual nature of the BLD and may support the notion of developing movement competency on one limb for enhanced CODS performance.

Effect of bilateral contraction on the ability and accuracy of rapid force production at submaximal force level

The present study aims to clarify the effects of bilateral contraction on the ability and accuracy of rapid force production at the submaximal force level. Eleven right-handed participants performed rapid gripping as fast and precisely as they could in unilateral (UL) and bilateral (BL) contractions in a standing position. Participants were required to impinge a grip force of 30% and 50% of their maximal voluntary contraction (MVC). Ability and accuracy of rapid force production were evaluated using the rate of force development (RFD) and force error, respectively. The data analysis did not observe a significant difference in the RFD between UL and BL contractions in both 30% (420±86 vs. 413±106%MVC/s, p = 0.34) and 50% of MVC (622±84 vs. 619±103%MVC/s, p = 0.77). Although the RFD to peak force ratio (RFD/PF) in BL contraction was lower than in UL in 30% of MVC (12.8±2.8 vs. 13.4±2.7, p = 0.003), it indicated a small effect size (d = 0.22) of the difference between UL and BL in RFD/PF. The absolute force error of BL contraction was higher than of UL contraction in 30% (4.67±2.64 vs. 3.64±1.13%MVC, p = 0.005) and 50% of MVC (5.53±2.94 vs. 3.53±0.71%MVC, p = 0.009). In addition, medium and large effect sizes were observed in absolute force error from 30% (d = 0.51) and 50% of MVC (d = 0.94), respectively. In conclusion, results indicated that the bilateral contraction reduced in the ability and accuracy of rapid force production at the submaximal force level. Nevertheless, the present results suggest that the noticeable effect of bilateral contraction is more prominent on the accuracy than in the ability of rapid force production at the submaximal force level.

Intermuscular coherence between homologous muscles during dynamic and static movement periods of bipedal squatting

Coordination of functionally coupled muscles is a key aspect of movement execution. Demands on coordinative control increase with the number of involved muscles and joints, as well as with differing movement periods within a given motor sequence. While previous research has provided evidence concerning inter- and intramuscular synchrony in isolated movements, compound movements remain largely unexplored. With this study, we aimed to uncover neural mechanisms of bilateral coordination through intermuscular coherence (IMC) analyses between principal homologous muscles during bipedal squatting (BpS) at multiple frequency bands (alpha, beta, and gamma). For this purpose, participants performed bipedal squats without additional load, which were divided into three distinct movement periods (eccentric, isometric, and concentric). Surface electromyography (EMG) was recorded from four homologous muscle pairs representing prime movers during bipedal squatting. We provide novel evidence that IMC magnitudes differ between movement periods in beta and gamma bands, as well as between homologous muscle pairs across all frequency bands. IMC was greater in the muscle pairs involved in postural and bipedal stability compared with those involved in muscular force during BpS. Furthermore, beta and gamma IMC magnitudes were highest during eccentric movement periods, whereas we did not find movement-related modulations for alpha IMC magnitudes. This finding thus indicates increased integration of afferent information during eccentric movement periods. Collectively, our results shed light on intermuscular synchronization during bipedal squatting, as we provide evidence that central nervous processing of bilateral intermuscular functioning is achieved through task-dependent modulations of common neural input to homologous muscles.

NEW & NOTEWORTHY It is largely unexplored how the central nervous system achieves coordination of homologous muscles of the upper and lower body within a compound whole body movement, and to what extent this neural drive is modulated between different movement periods and muscles. Using intermuscular coherence analysis, we show that homologous muscle functions are mediated through common oscillatory input that extends over alpha, beta, and gamma frequencies with different synchronization patterns at different movement periods.

Bilateral deficit in strength but not rapid force during maximal handgrip contractions

The purpose of this experiment was to evaluate the bilateral index in force and electromyographic (EMG) responses for the dominant and non-dominant hands during maximal handgrip contractions in males and females. Thirty-two right-handed participants (16 females) performed maximal unilateral and bilateral handgrip contractions on two separate visits. Bilateral indices were computed for maximal force, rate of force development (RFD₁₀₀), EMG amplitude, and the rate of EMG rise (RER). There was a bilateral deficit for maximal force in the dominant (-4.98 ± 7.39%, p < 0.001; d = 0.674) but not the non-dominant hand (-1.57 ± 9.10%, p = 0.334; d = 0.173). No deficits were observed for rapid force. The non-dominant flexor carpi radialis showed a bilateral facilitation in EMG amplitude (+12.32 ± 19.29%, p < 0.001; d = 0.638), yet a bilateral deficit for RER (-22.10 ± 27.80%, p < 0.001; d = 0.795). No sex differences were observed for any of the bilateral indices. These data suggest that maximal but not rapid force is susceptible to a bilateral deficit during contractions of the hands. The EMG responses did not parallel the force data. We show sex does not influence the magnitude or direction of the bilateral index in this muscle group.

Factors influencing bilateral deficit and inter-limb asymmetry of maximal and explosive strength: motor task, outcome measure and muscle group

PURPOSE

The purpose of the present study was to investigate the influence of strength outcome [maximal voluntary contraction (MVC) torque vs. rate of torque development (RTD)], motor task (unilateral vs. bilateral) and muscle group (knee extensors vs. flexors) on the magnitude of bilateral deficits and inter-limb asymmetries in a large heterogeneous group of athletes.

METHODS

259 professional/semi-professional athletes from different sports (86 women aged 21 ± 6 years and 173 men aged 20 ± 5 years) performed unilateral and bilateral "fast and hard" isometric maximal voluntary contractions of the knee extensors and flexors on a double-sensor dynamometer. Inter-limb asymmetries and bilateral deficits were compared across strength outcomes (MVC torque and multiple RTD measures), motor tasks and muscle groups.

RESULTS

Most RTD outcomes showed greater bilateral deficits than MVC torque for knee extensors, but not for knee flexors. Most RTD outcomes, not MVC torque, showed higher bilateral deficits for knee extensors compared to knee flexors. For both muscle groups, all RTD measures resulted in higher inter-limb asymmetries than MVC torque, and most RTD measures resulted in greater inter-limb asymmetries during unilateral compared to bilateral motor tasks.

CONCLUSIONS

The results of the present study highlight the importance of outcome measure, motor task and muscle group when assessing bilateral deficits and inter-limb asymmetries of maximal and explosive strength. Compared to MVC torque and bilateral tasks, RTD measures and unilateral tasks could be considered more sensitive for the assessment of bilateral deficits and inter-limb asymmetries in healthy professional/semi-professional athletes.

Effects of Additional Load on the Occurrence of Bilateral Deficit in Counter-Movement and Squat Jumps

Purpose: A vertical jump (VJ) is a common task performed in several sports, with the height achieved correlated to skilled performance. Loaded VJs are often used in the training of recreational and professional athletes. The bilateral deficit (BLD), which refers to the difference between the heights achieved by a bilateral jump and the sum of two unilateral jumps, has not been reported for loaded jumps and the findings for unloaded jumps are inconclusive. The purpose of this study was threefold: (a) to quantify and compare BLD in countermovement (CMJ) and squat jumps (SJ), (b) to explore the effects of an additional 10% of body weight (BW) load on the BLD in both CMJ and SJ, and (c) examine the relationship between magnitude of BLD and jump performance in both jumps and conditions. Methods: Forty participants (22 for CMJ and 18 for SJ) performed a bilateral jump and unilateral jumps on each leg with and without an added load equivalent to 10% of each participant's bodyweight. Results: BLD was evident in all conditions, with CMJ BLD values nearly double those for the SJ. The extra load did not affect the magnitude of BLD. BLD had a significant correlation with unilateral jump height, expect for the 110%BW SJ. Conclusions: BLD is present in SJs and CMJs at both loaded and unloaded conditions. The SJs have about half of the BLD observed in CMJs regardless of additional load. Participants who had higher single leg jumps seemed to also have higher BLDs, but there was no evidence of association between the bilateral jump height and BLD.

Bilateral deficit of spring-like behaviour during hopping in sprinters

PURPOSE

Unilateral leg stiffness is a key contributor to sprint running speed, thereby great bilateral deficit (BLD) of leg stiffness would be expected to be observed in sprinters. However, it remains clear only BLD of leg stiffness at the preferred hopping frequency in non-sprinters. The purpose of this study was to clarify the BLD of spring-like behaviour in hopping at various frequencies and the effect of chronic adaptation via sprint running experience on BLD during the hopping.

METHODS

Fifteen male experienced sprinters and 12 male novices participated in this study. They were instructed to hop in place at three frequencies (2.0, 2.5, and 3.0 Hz), and to perform hopping with maximal effort. Ground reaction forces (GRF) of both legs during the hopping were recorded using two force plates.

RESULTS

At higher hopping frequencies during the unilateral and bilateral hopping, smaller peak value of vertical GRF (F _max) and greater leg stiffness (K _leg) were significantly observed. The BLD index of F _max and the BLD index of K _leg were significantly smaller at higher hopping frequencies. No significant differences of BLD index of F _max and BLD index of K _leg were observed between sprinters and novices.

CONCLUSION

Our results demonstrate that neuromuscular inhibition in the contralateral leg changes during the hopping based on hopping frequency. This suggests that plyometric training in the beginning of rehabilitation should involve bilateral jumping at a high frequency. In experienced sprinters, detailed mechanics of chronic neuromuscular adaptation via unilateral facilitation of spring-like behaviour should be assessed by measuring electromyographic activity.

Bilateral Strength Deficit Is Not Neural in Origin; Rather Due to Dynamometer Mechanical Configuration

During maximal contractions, the sum of forces exerted by homonymous muscles unilaterally is typically higher than the sum of forces exerted by the same muscles bilaterally. However, the underlying mechanism(s) of this phenomenon, which is known as the bilateral strength deficit, remain equivocal. One potential factor that has received minimal attention is the contribution of body adjustments to bilateral and unilateral force production. The purpose of this study was to evaluate the plantar-flexors in an innovative dynamometer that permitted the influence of torque from body adjustments to be adapted. Participants were identically positioned between two setup configurations where torques generated from body adjustments were included within the net ankle torque (locked-unit) or independent of the ankle (open-unit). Twenty healthy adult males performed unilateral and bilateral maximal voluntary isometric plantar-flexion contractions using the dynamometer in the open and locked-unit mechanical configurations. While there was a significant bilateral strength deficit in the locked-unit (p = 0.01), it was not evident in the open-unit (p = 0.07). In the locked-unit, unilateral torque was greater than in the open-unit (p<0.001) and this was due to an additional torque from the body since the electromyographic activity of the agonist muscles did not differ between the two setups (p>0.05). This study revealed that the mechanical configuration of the dynamometer and then the body adjustments caused the observation of a bilateral strength deficit.

Peak torque and rate of torque development influence on repeated maximal exercise performance: contractile and neural contributions

Rapid force production is critical to improve performance and prevent injuries. However, changes in rate of force/torque development caused by the repetition of maximal contractions have received little attention. The aim of this study was to determine the relative influence of rate of torque development (RTD) and peak torque (T_peak) on the overall performance (i.e. mean torque, T_mean) decrease during repeated maximal contractions and to investigate the contribution of contractile and neural mechanisms to the alteration of the various mechanical variables. Eleven well-trained men performed 20 sets of 6-s isokinetic maximal knee extensions at 240°·s^-1, beginning every 30 seconds. RTD, T_peak and T_mean as well as the Rate of EMG Rise (RER), peak EMG (EMG_peak) and mean EMG (EMG_mean) of the vastus lateralis were monitored for each contraction. A wavelet transform was also performed on raw EMG signal for instant mean frequency (if_mean) calculation. A neuromuscular testing procedure was carried out before and immediately after the fatiguing protocol including evoked RTD (eRTD) and maximal evoked torque (eT_peak) induced by high frequency doublet (100 Hz). T_mean decrease was correlated to RTD and T_peak decrease (R²=0.62; p<0.001; respectively β=0.62 and β=0.19). RER, eRTD and initial if_mean (0-225 ms) decreased after 20 sets (respectively -21.1±14.1, -25±13%, and ~20%). RTD decrease was correlated to RER decrease (R²=0.36; p<0.05). The eT_peak decreased significantly after 20 sets (24±5%; p<0.05) contrary to EMG_peak (-3.2±19.5 %; p=0.71). Our results show that reductions of RTD explained part of the alterations of the overall performance during repeated moderate velocity maximal exercise. The reductions of RTD were associated to an impairment of the ability of the central nervous system to maximally activate the muscle in the first milliseconds of the contraction.

Considerations for Single and Double Leg Drop Jumps: Bilateral Deficit, Standardizing Drop Height, and Equalizing Training Load

Bilateral deficit is well documented; however, bilateral deficit is not present in all tasks and is more likely in dynamic activities than isometric activities. No definitive mechanism(s) for bilateral deficit is known but an oft cited mechanism is lower activation of fast twitch motor units. The aim of this study was to produce comparable and consistent one and two legged drop jumps to examine bilateral deficit in elite power athletes and elite endurance athletes. Seven power athletes and seven endurance athletes performed single and double leg drop jumps from a range of heights that equalized loading per leg in terms of: height dropped, energy absorbed, and momentum absorbed. Force and motion data were collected at 800 Hz. Bilateral deficit for jump height, peak concentric force, and peak concentric power were calculated. Power athletes had a significantly greater (P< .05) bilateral deficit for jump height and peak power, possibly due to power athletes having more fast twitch motor units, however, endurance athletes generally had a bilateral surfeit which could confound this inference. Results indicate that equalizing loading by impulse per leg is the most appropriate and that a consistent drop height can be obtained with a short 10 minute coaching session.

Rate of force development as a measure of muscle damage

This study tested the hypothesis that rate of force development (RFD) would be a more sensitive indirect marker of muscle damage than maximum voluntary isometric contraction (MVC) peak torque. Ten men performed one concentric cycling and two eccentric cycling (ECC1, ECC2) bouts for 30 min at 60% of maximal concentric power output with 2 weeks between bouts. MVC peak torque, RFD, and vastus lateralis electromyogram amplitude and mean frequency were measured during a knee extensor MVC before, immediately after and 1-2 days after each bout. The magnitude of decrease in MVC peak torque after exercise was greater (P < 0.05) for ECC1 (11-25%) than concentric cycling (2-12%) and ECC2 (0-16%). Peak RFD and RFD from 0-30 ms, 0-50 ms, 0-100 ms, to 0-200 ms decreased (P < 0.05) immediately after all cycling bouts without significant differences between bouts, but RFD at 100-200 ms interval (RFD(100-200)) decreased (P < 0.05) at all time points after ECC1 (24-32%) and immediately after ECC2 (23%), but did not change after CONC. The magnitude of decrease in RFD(100-200) was 7-19% greater than that of MVC peak torque after ECC1 (P < 0.05). It is concluded that RFD(100-200) is a more specific and sensitive indirect marker of eccentric exercise-induced muscle damage than MVC peak torque.

Impaired neural drive in patients with low back pain

BACKGROUND

Control of trunk movement relies on the integration between central neuronal circuits and peripheral skeletomuscular activities and it can be altered by pain. There is increasing evidence that there are deficits within the central nervous system controlling the trunk muscles in people with low back pain (LBP). However, it is unclear how LBP impacts upon neural drive to back muscles at different levels of voluntary contraction. Therefore, the purpose of this study was to investigate if neural drive is impaired in these patients.

METHODS

Seventeen patients with LBP and 11 healthy controls were recruited. Bilateral electromyographic (EMG) recordings were obtained from the erector spinae (ES) muscles at two vertebral levels (T12 and L4). Participants performed a series of brief isometric back extensions (50-100% maximum voluntary contraction - MVC), during which transcranial magnetic stimulation was delivered. The size of the evoked (superimposed) twitch was measured using dynamometry.

RESULTS

The size of the superimposed twitch decreased linearly with increasing contraction strength in the controls; however, this linear relationship was not observed in the patients. Additionally, patients had larger superimposed twitches and longer time-to-peak amplitudes during MVCs than those observed in controls. Furthermore, patients had lower MVC and root-mean-square EMG activity of ES muscles during MVCs.

CONCLUSIONS

A decline of central neural drive to the back muscles at high level of voluntary contraction was observed in patients with LBP. These results suggest that it might be pertinent to include neuromuscular facilitation programmes and therapeutic exercise utilizing high voluntary contractions for patients with LBP.