The persistence of quadriceps weakness represents a major concern following anterior cruciate ligament reconstruction (ACLR). The underlying adaptations occurring in the activity of spinal ...motoneurons are still unexplored. This study examined the discharge patterns of large populations of motor units (MUs) in the vastus lateralis (VL) and vastus medialis muscles following ACLR. Nine ACLR individuals and 10 controls performed unilateral trapezoidal contractions of the knee extensor muscles at 35%, 50% and 70% of the maximal voluntary isometric force (MVIF). High‐density surface electromyography (HDsEMG) was used to record the myoelectrical activity of the vasti muscles in both limbs. HDsEMG signals were decomposed with a convolutive blind source separation method and MU properties were extracted and compared between sides and groups. The ACLR group showed a lower MVIF on the reconstructed side compared to the contralateral side (28.1%; P < 0.001). This force deficit was accompanied by reduced MU discharge rates (∼21%; P < 0.05), lower absolute MU recruitment and derecruitment thresholds (∼22% and ∼22.5%, respectively; P < 0.05) and lower input–output gain of motoneurons (27.3%; P = 0.009). Deficits in MU discharge rates of the VL and in absolute recruitment and derecruitment thresholds of both vasti MUs were associated with deficits in MVIF (P < 0.05). A strong between‐side correlation was found for MU discharge rates of the VL of ACLR individuals (P < 0.01). There were no significant between‐group differences (P > 0.05). These results indicate that mid‐ to long‐term strength deficits following ACLR may be attributable to a reduced neural drive to vasti muscles, with potential changes in excitatory and inhibitory synaptic inputs.
Key points
Impaired expression and control of knee extension forces is common after anterior cruciate ligament reconstruction and is related to high risk of a second injury.
To provide novel insights into the neural basis of this impairment, the discharge patterns of motor units in the vastus lateralis and vastus medialis were investigated during voluntary force contractions.
There was lower knee extensor strength on the reconstructed side with respect to the contralateral side, which was explained by deficits in motor unit discharge rate and an altered motoneuronal input–output gain. Insufficient excitatory inputs to motoneurons and increased inhibitory afferent signals potentially contributed to these alterations.
These results further our understanding of the neural underpinnings of quadriceps weakness following anterior cruciate ligament reconstruction and can help to develop effective rehabilitation protocols to regain muscle strength and reduce the risk of a second injury.
figure legend Changes in activity of motor units underlying deficits in knee extension strength following anterior cruciate ligament reconstruction (ACLR). The behaviour of motor units was assessed by decomposing high‐density surface electromyographic signals that were recorded from the vasti muscles of ACLR and control soccer players during submaximal trapezoidal contractions. The lower knee extension strength of the reconstructed side with respect to the contralateral side was explained by deficits in motor unit recruitment and derecruitment thresholds, by deficits in motor unit discharge rate of the vastus lateralis and by an altered input–output gain of motoneurons. Synaptic alterations and changes at muscle unit level potentially contributed to changes in motor unit activity. Correction made on 15 November 2021, after first online publication: The two preceding sentences have been updated to provide greater clarity.
The use of knee braces early after anterior cruciate ligament (ACL) reconstruction is a controversial issue. The study preliminarily compares the effect of a traditional brace blocked in knee ...extension and a new functional brace equipped with a spring resistance on walking and strength performance early after ACL reconstruction performed in the acute/subacute stage.
14 ACL-reconstructed patients wore either a traditional (Control group: CG, 7 subjects) or a new functional brace (Experimental group: EG 7 subjects) until the 30
post-operative day. All patients were tested before surgery (T0), 15, 30, and 60 days after surgery (T1, T2, and T3, respectively). Knee angular displacement and ground reaction forces (GRF) during the stance phase of the gait cycle were analyzed at each session and, at T3, maximal voluntary isometric contraction (MVIC) for knee flexor/extensor muscles was performed. Limb symmetry indexes (LSI) of GRF and MVIC parameters were calculated.
At T3, EG showed greater peak knee flexion angle of injured limb compared to CG (41 ± 2° vs 32 ± 1°, p < 0.001). During weight acceptance, a significant increase of anteroposterior GRF peak and vertical impulse from T1 to T3 was observed in the injured limb in EG (p < 0.05) but not in CG (p > 0.05). EG showed a greater side-to-side LSI of weight acceptance peak of anteroposterior GRF at T2 (113 ± 23% vs 69 ± 11%, p < 0.05) and T3 (112 ± 23% vs 84 ± 10%, p < 0.05).
The preliminary findings from this study indicate that the new functional brace did help in improving gait biomechanical pattern in the first two months after ACL reconstruction compared to a traditional brace locked in knee extension.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The effort of the rehabilitation journey to solve the several known functional and clinical problems after anterior cruciate ligament reconstruction should be directed toward implementing effective ...recovery strategies starting the day after surgery. Resistance training is a reliable approach to restore general knee function, but in the early postoperative stages, it may be difficult to apply proper loading strategies to obtain tangible improvements owing to surgery-related impairments. Accordingly, applying continuous light resistance during functional tasks such as gait may help to address this issue. As such, bracing models that provide resistance to knee motion have recently been developed and have been shown to help in restoring a proper walking pattern in terms of moment and range-of-motion symmetry. Therefore, the adoption of such bracing models may be regarded as a suitable option to consider to boost the achievement of rehabilitative milestones, therefore generally improving rehabilitation quality.
Introduction: High intensity functional trainings (HIFT) are among the most common and popular training modalities. The aim of the present study was to examine the physiological characteristics of a ...group of HIFT competitive athletes both in a laboratory and field setting. Methods: Twenty HIFT athletes, 10 men (29 ± 5.3 years) and 10 women (30 ± 3.2 years), were evaluated in the laboratory for anthropometric characteristics, VO2peak, lactate threshold, maximal anaerobic power, maximal voluntary isometric and isokinetic strength, and muscle power during a countermovement jump. Athletes were also monitored in the field by measuring VO2 and lactate during a training session. Results: HIFT competitive athletes reached high levels in VO2peak (52.9 ± 5.67 ml·kg-1·min-1 in men; 52.4 ± 6.17 ml·kg-1·min-1 in women), VO2 at lactate threshold (79.7% of VO2peak in men; 74.5% of VO2peak in women), maximal anaerobic power (7.6 ± 1.32 W·kg-1 in men; 5.0 ± 1.13 W·kg-1 in women; p < .05), maximal voluntary knee extension isometric strength (11.7 ± 1.43 N·kg-1 in men; 9.5 ± 2.25 N·kg-1 in women; p < .05) and isokinetic strength (281.4 ± 31.56 N·kg-1 in men; 243.1 ± 44.13 N·kg-1 in women; p < .05), and muscle power during a countermovement jump (54 ± 5.9 W·kg-1 in men; 40 ± 4.8 W·kg-1 in women; p < .05). VO2peak during the on-field training session (50.6 ± 3.82 ml·kg-1·min-1 in men; 51.9 ± 5.76 ml·kg-1·min-1 in women) and lactate production (10.4 ± 0.69 mmol·l-1 in men; 9.7 ± 0.96 mmol·l-1 in women) revealed the high intensity nature of HIFT. Conclusions: Overall, HIFT athletes show exceptional performances in physiological components that are key to many different sports. The lack of specialization in exclusively one domain of physical fitness reveals the comprehensive nature of this training methodology.
IntroductionHamstring strength deficits have been identified as risk factors for ACL and muscular injuries, with hamstring strain being the most prevalent muscle injuries in soccer. The aim of this ...study was to investigate hamstring eccentric strength before and after a soccer match in soccer athletes.Material and MethodsHamstring eccentric strength was measured in 64 healthy male and female competitive football athletes (14-25 years) during the execution of the Nordic hamstring exercise (NHE test) before and after a soccer match. Anterior-knee laxity (AKL) was quantified as well.ResultsMean and absolute eccentric hamstring peak torque decreased by 24.5 Nm (p<0.005) and 21.9 Nm (p<0.0005) in females, whereas males improved by 19.9 Nm (p=0.01) and 20.9 Nm (p=0.02), respectively. Hamstring’s total work in females decreased by 831.1 J (p<0.0005) compared to the males’ reduction of 235.3 J. Both pre- vs. post-match intersex mean and absolute eccentric HS peak torque changes were significant (p<0.0005), as the changes in HS total work (p=0.007). Pre- vs. post-match AKL difference and dominant vs. nondominant limb comparison of strength parameters were not significantly different. Younger female athletes (14-19 years old) presented a greater decrease in mean and absolute peak HS eccentric strength than those in older female and overall male athletes.ConclusionsHS eccentric strength and work differ based on the athlete’s sex, as measured by the NHE test. Mean peak, absolute peak, and total work showed greater reductions in females than in males. The 14- to 19-year-old female athletes subgroup experienced the highest reduction.
Introduction: Among high intensity trainings, high intensity functional training (HIFT) represent one of the most recent developments. The aim of the present study was to investigate the differences ...between a group of competitive (CMP) HIFT athletes and a group of age- and gender-matched beginner (BGN) HIFT athletes, to clarify the physiological characteristics of each group and the reasons for differences. Methods: 10 BGN (32.5 ± 6.2 years) and 10 CMP (29.0 ± 5.4 years) athletes, were included in the study and were evaluated for anthropometry, VO2peak, lactate threshold, isometric and isokinetic leg maximal power and strength, handgrip and maximal anaerobic power. Results: Compared to BGN athletes, CMP reached higher levels of VO2peak (56.1 ± 2.89 ml·kg-1·min-1 CMP vs. 46.5 ± 6.86 ml·kg-1·min-1 BGN; p < .001), lower limb maximal power (4.5 ± 0.42 W·kg-1 CMP vs. 2.9 ± 0.67 W·kg-1 BGN; p < .001), maximal handgrip strength (61.1 ± 8.20 N·kg-1 CMP vs. 45.1 ± 7.58 N·kg-1 BGN; p < .001), maximal knee extension isometric strength (11.7 ± 1.43 N·kg-1 CMP vs. 9.1 ± 2.00 N·kg-1 BGN; p < .05), isokinetic strength (281.3 ± 28.18 N·kg-1 CMP vs. 234.6 ± 26.15 N·kg-1 BGN; p < .05) and anaerobic peak power (639.1 ± 125.54 W·kg-1 CMP vs. 442.7 ± 155.96 W· kg-1 BGN; p > .006), while anaerobic capacity did not show significant differences (101.8 ± 9.33 kJ CMP vs. 87.0 ± 28.37 kJ BGN; p = .1). Conclusions: CMP athletes showed greater physiological adaptations in aerobic fitness and strength than BGN. Differences may be attributed to the technical skills acquired by CMP and not only to the physiological adaptations induced by the specific training. The lack of differences in anaerobic capacity is likely due to an early and fast improvement in BGN, compared to other parameters.
PURPOSEQuadriceps weakness and asymmetrical loading of lower limbs are two major issues following anterior cruciate ligament reconstruction (ACLR). The aim of this study was to evaluate the ...effectiveness of a 6-week training protocol involving neuromuscular electrical stimulations (NMES) of the quadriceps muscle superimposed on repeated sit-to-stand-to-sit exercises (STSTS), as an additional treatment to standard rehabilitation, from the 15th to the 60th day following ACLR.
METHODSSixty-three ACLR patients were randomly allocated to one of the three treatment groupsNMES superimposed on STSTS (NMES+STSTS), STSTS only, or no additional treatment (NAT) to standard rehabilitation. Maximal isometric strength of knee extensor and flexor muscles was measured 60 and 180 days after surgery. Asymmetry in lower extremity loading was measured during a sit-to-stand movement at 15, 30, 60 and 180 days after surgery and during a countermovement jump 180 days after surgery by means of two adjacent force platforms placed under each foot.
RESULTSThe NMES+STSTS participants showed higher muscle strength of the knee extensors, which was accompanied by lower perception of pain, and higher symmetry in lower extremity loading compared to STSTS-only and NAT participants after both 60 and 180 days from surgery. Participants in the STSTS-only treatment group showed higher symmetry in lower extremity loading compared to those in the NAT group 60 days post-surgery.
CONCLUSIONThese results suggest that an early intervention based on NMES superimposed to repeated STSTS exercises is effective for recovering quadriceps strength and symmetry in lower extremity loading by the time of return to sport.
OBJECTIVES:It is well known that alterations in landing mechanics persist for years after anterior cruciate ligament reconstruction (ACL-R). Nevertheless, existing literature is controversial in ...reporting successful or unsuccessful recovery of prelanding muscle activation timing after ACL-R. The study aimed at comparing myoelectric and kinematic patterns during landing tasks between ACL-R and healthy subjects.
DESIGN:Cross-sectional study.
SETTING:Institutional research laboratory.
PATIENTS AND INTERVENTION:Fifteen male athletes after ACL-R using patellar tendon and 11 using hamstrings autograft at the time of return to sport were recruited. Fifteen healthy athletes served as control group. Participants performed 4 different single-leg landing tasks arriving onto a force plate.
MAIN OUTCOME MEASURES:Electromyographic (EMG) activity of knee extensors and flexors, normalized vertical ground reaction force (vGRF), and knee angular displacement were recorded.
RESULTS:In all the tasks, preimpact EMG duration was longer in ACL-R (112 ± 28 ms in the knee extensors; 200 ± 34 ms in the knee flexors) compared with healthy participants (74 ± 19 ms in the knee extensors; 153 ± 29 ms in the knee flexors; P < 0.05). Initial contact (IC) and maximum postimpact knee angle were lower in ACL-R (9 ± 7 degrees at IC; 39 ± 12 degrees at maximum flexion) compared with healthy participants (17 ± 9 degrees at IC; 52 ± 15 degrees at maximum flexion; P < 0.05). Normalized vGRF was higher in ACL-R compared with healthy participants (3.4 ± 0.5 and 2.7 ± 0.6; P < 0.05).
CONCLUSIONS:At the time of return to sport, ACL-R subjects showed altered motor control strategies of single-leg landings. These alterations may lead to uncoordinated movement, hence increasing the risk of reinjury.
We evaluated the effects of different exercise types suitable for a home/work setting on the postprandial glucose response. Twenty-three healthy, active, young individuals performed one of two ...studies (12 in Study 1 and 11 in Study 2), with four randomized protocols each. After a meal high in carbohydrate content (1 g of carbohydrate per kg of body weight), in Study 1, participants performed 30 min of either walking (WALK), bench stepping exercise (STEP) or isometric wall squat (SQUAT); in Study 2, participants performed 30 min of either walking (WALK), neuromuscular electrical stimulation alone (P_NMES) or superimposed on voluntary muscle contraction (VC_NMES). In both studies, participants performed a prolonged sitting condition (CON) that was compared to the exercise sessions. In Study 1, WALK and STEP significantly reduced the glucose peak compared to CON (p < 0.011). In Study 2, the peak was significantly reduced in WALK compared to CON, P_NMES and VC_NMES (p < 0.011) and in VC_NMES compared to CON and P_NMES (p < 0.011). A significant reduction of 3 h glucose iAUC was found for WALK and VC_NMES compared to CON and P_NMES (p < 0.033). In conclusion, WALK is the most effective strategy for improving the postprandial glycemic response. However, STEP and VC_NMES can also be used for reducing postprandial glycemia.
Background:
The acute effects of exercise on anterior knee laxity (AKL) and anterior knee stiffness (AKS) have been documented in healthy participants, but only limited evidence has been provided for ...athletes cleared to return to sports after anterior cruciate ligament (ACL) reconstruction (ACLR).
Purpose/Hypothesis:
The purpose was to determine if 45 minutes of a soccer match simulation lead to acute changes in AKL and AKS in soccer players returning to sport within 12 months after ACLR. We hypothesized that the reconstructed knee of the ACLR group would exhibit an altered response to sport-specific exercise.
Study Design:
Controlled laboratory study.
Methods:
A total of 13 soccer players cleared to return to sport after ACLR and 13 healthy control soccer players matched for age, physical activity level, limb dominance, and anthropometric characteristics were recruited. To assess the effects of a standardized soccer match simulation (Soccer Aerobic Field Test SAFT45) on AKL and AKS, an arthrometric evaluation was carried out bilaterally before and immediately after SAFT45. To conduct a comprehensive examination of the force-displacement curve, the absolute and side-to-side difference (SSD) values of both AKL and AKS were extracted at 67, 134, and 200 N.
Results:
The ACLR and control groups showed similar AKL and AKS at baseline (P > .05). In response to SAFT45, laxity increased bilaterally at all force levels by 14% to 17% only in the control group (P < .025). Similarly, AKS at 134 and 200 N decreased in response to SAFT45 only in the control group (10.5% and 20.5%, respectively; P < .025). After SAFT45, the ACLR group had 1.9 and 2.5 times higher SSDs of AKS at 67 and 134 N compared with the control group, respectively (P < .025), as well as a 1.9 times higher SSD of AKS at 134 N compared with baseline (P = .014).
Conclusion:
Soccer players at the time of return to sport after ACLR showed an altered mechanical response to a sport-specific match simulation consisting of bilaterally unchanged AKL and AKS.
Clinical Relevance:
Soccer players showing altered AKL and AKS in response to exercise after ACLR may not be ready to sustain their preinjury levels of sport, thus potentially increasing the risk of second ACL injuries.
PDF
