The architectural and morphological adaptations of the hamstrings in response to training with different exercises have not been explored.
To evaluate changes in biceps femoris long head (BF
) ...fascicle length and hamstring muscle size following 10-weeks of Nordic hamstring exercise (NHE) or hip extension (HE) training.
30 recreationally active male athletes (age, 22.0±3.6 years; height, 180.4±7 cm; weight, 80.8±11.1 kg) were allocated to 1 of 3 groups: (1) HE training (n=10), NHE training (n=10), or no training (control, CON) (n=10). BF
fascicle length was assessed before, during (Week 5) and after the intervention with a two-dimensional ultrasound. Hamstring muscle size was determined before and after training via MRI.
Compared with
, BF
fascicles were lengthened in the NHE and HE groups at
(d=1.12-1.39, p<0.001) and
(d=1.77-2.17, p<0.001) and these changes did not differ significantly between exercises (d=0.49-0.80, p=0.279-0.976). BF
volume increased more for the HE than the NHE (d=1.03, p=0.037) and CON (d=2.24, p<0.001) groups. Compared with the CON group, both exercises induced significant increases in semitendinosus volume (d=2.16-2.50, ≤0.002) and these increases were not significantly different (d=0.69, p=0.239).
NHE and HE training both stimulate significant increases in BF
fascicle length; however, HE training may be more effective for promoting hypertrophy in the BF
.
•Biceps femoris long head fascicle and sarcomere lengths increase after 3 weeks of Nordic hamstring exercise training.•Architectural adaptations occurred only in the distal portion of the ...muscle.•Increases in fascicle length in response to 3 weeks of exercise training were not the result of serial sarcomere addition.
Eccentric exercise increases muscle fascicle lengths; however, the mechanisms behind this adaptation are still unknown. This study aimed to determine whether biceps femoris long head (BFlh) fascicle length increases in response to 3 weeks of eccentric exercise training are the result of an in-series addition of sarcomeres within the muscle fibers.
Ten recreationally active participants (age = 27 ± 3 years; mass = 70 ± 14 kg; height = 174 ± 9 cm; mean ± SD) completed 3 weeks of Nordic hamstring exercise (NHE) training on a custom exercise device that was instrumented with load cells. We collected in vivo sarcomere and muscle fascicle images of the BFlh in 2 regions (central and distal) by using microendoscopy and 3 dimension ultrasonography. We then estimated sarcomere length, sarcomere number, and fascicle length before and after the training intervention.
Eccentric knee flexion strength increased after the training (15%; p < 0.001; ηp2 = 0.75). Further, we found a significant increase in fascicle length (21%; p < 0.001; ηp2 = 0.81) and sarcomere length (17%; p < 0.001; ηp2 = 0.90) in the distal but not in the central portion of the muscle. The estimated number of sarcomeres in series did not change in either region.
Fascicle length adaptations appear to be heterogeneous in the BFlh in response to 3 weeks of NHE training. An increase in sarcomere length, rather than the addition of sarcomeres in series, appears to underlie increases in fascicle length in the distal region of the BFlh. The mechanism driving regional increases in fascicle and sarcomere length remains unknown, but we speculate that it may be driven by regional changes in the passive tension of muscle or connective tissue adaptations.
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For many sporting activities, initial speed rather than maximal speed would be considered of greater importance to successful performance. The purpose of this study was to identify the relationship ...between strength and power and measures of first-step quickness (5-m time), acceleration (10-m time), and maximal speed (30-m time). The maximal strength (3 repetition maximum 3RM), power (30-kg jump squat, countermovement, and drop jumps), isokinetic strength measures (hamstring and quadriceps peak torques and ratios at 60 degrees .s(-1) and 300 degrees .s(-1)) and 5-m, 10-m, and 30-m sprint times of 26 part-time and full-time professional rugby league players (age 23.2 +/- 3.3 years) were measured. To examine the importance of the strength and power measures on sprint performance, a correlational approach and a comparison between means of the fastest and slowest players was used. The correlations between the 3RM, drop jump, isokinetic strength measures, and the 3 measures of sport speed were nonsignificant. Correlations between the jump squat (height and relative power output) and countermovement jump height and the 3 speed measures were significant (r = -0.43 to -0.66, p < 0.05). The squat and countermovement jump heights as well as squat jump relative power output were the only variables found to be significantly greater in the fast players. It was suggested that improving the power to weight ratio as well as plyometric training involving countermovement and loaded jump-squat training may be more effective for enhancing sport speed in elite players.
Does the Nordic hamstring exercise (NHE) prevent hamstring injuries when included as part of an injury prevention intervention?
Systematic review and meta-analysis.
We considered the population to be ...any athletes participating in any sporting activity, the intervention to be the NHE, the comparison to be usual training or other prevention programmes, which did not include the NHE, and the outcome to be the incidence or rate of hamstring injuries.
The effect of including the NHE in injury prevention programmes compared with controls on hamstring injuries was assessed in 15 studies that reported the incidence across different sports and age groups in both women and men.
MEDLINE via PubMed, CINAHL via Ebsco, and OpenGrey.
There is a reduction in the overall injury risk ratio of 0.49 (95% CI 0.32 to 0.74, p=0.0008) in favour of programmes including the NHE. Secondary analyses when pooling the eight randomised control studies demonstrated a small increase in the overall injury risk ratio 0.52 (95% CI 0.32 to 0.85, p=0.0008), still in favour of the NHE. Additionally, when studies with a high risk of bias were removed (n=8), there is an increase of 0.06 in the risk ratio to 0.55 (95% CI 0.34 to 0.89, p=0.006).
Programmes that include the NHE reduce hamstring injuries by up to 51%. The NHE essentially halves the rate of hamstring injuries across multiple sports in different athletes.
PROSPERO CRD42018106150.
Purpose
Comparing the MRI features of the grafts between a group of patients treated with an over-the-top anterior cruciate ligament reconstruction technique that preserves the hamstring attachment ...and a control group with a classical reconstruction technique.
Methods
Patients were assigned to a standard reconstruction technique or an Over-the-top plus lateral plasty technique. All patients underwent preoperative, 4-months and 18-months MRI; together with a clinical evaluation with KOOS and KT1000 laxity assessment. MRI study involved different parameters: the “Graft” was evaluated with the continuity, Howell Grading system, presence of liquid and signal noise quotient. The “Tibial Tunnel” was evaluated with the signal noise quotient, presence of edema or liquid and tunnel widening. All points assigned to each parameter formed a composite score ranging from 0–10. Tunnel and graft positioning were evaluated.
Results
At 18-month 20 MRIs (10 each group) were available, demographics were not significantly different between groups. The non-detached group showed significantly less liquid within the graft at 4-months (
p
= 0.008) and 18-months (
p
= 0.028), the tunnel was significantly smaller (
p
< 0.05) and less enlarged at both follow-ups (
p
< 0.05), signal noise quotient of the intra-tunnel graft was lower at 18-months (
p
< 0.05). The total score of the non-detached group saw a significant improvement at 4-months (
p
= 0.006) that remained stable at 18-months (n.s.).
Conclusions
Hamstring grafts, which tibial insertions were preserved, showed better MRI features at 4-and 18-months follow-up, especially in terms of liquid effusion, tunnel enlargement and signal noise quotient.
Level of evidence
IV.
In this study, we aimed to clarify the characteristics of neuromuscular function, kinetics, and kinematics of the lower extremity during sprinting in track and field athletes with a history of strain ...injury. Ten male college sprinters with a history of unilateral hamstring injury performed maximum effort sprint on an athletic track. The electromyographic (EMG) activity of the long head of the biceps femoris (BFlh) and gluteus maximus (Gmax) muscles and three-dimensional kinematic data were recorded. Bilateral comparisons were performed for the EMG activities, pelvic anterior tilt angle, hip and knee joint angles and torques, and the musculotendon length of BFlh. The activity of BFlh in the previously injured limb was significantly lower than that in the uninjured limb during the late-swing phase of sprinting (p < 0.05). However, the EMG activity of Gmax was not significantly different between the previously injured and uninjured limbs. Furthermore, during the late-swing phase, a significantly more flexed knee angle (p < 0.05) and a decrease in BFlh muscle length (p < 0.05) were noted in the injured limb. It was concluded that previously injured hamstring muscles demonstrate functional deficits during the late swing phase of sprinting in comparison with the uninjured contralateral muscles.
The distal semitendinosus tendon is commonly harvested for anterior cruciate ligament reconstruction, inducing substantial morbidity at the knee. The aim of this study was to probe how morphological ...changes of the semitendinosus muscle after harvest of its distal tendon for anterior cruciate ligament reconstruction affects knee flexion strength and whether the knee flexor synergists can compensate for the knee flexion weakness. Ten participants 8–18 months after anterior cruciate ligament reconstruction with an ipsilateral distal semitendinosus tendon autograft performed isometric knee flexion strength testing (15°, 45°, 60°, and 90°; 0° = knee extension) positioned prone on an isokinetic dynamometer. Morphological parameters extracted from magnetic resonance images were used to inform a musculoskeletal model. Knee flexion moments estimated by the model were then compared with those measured experimentally at each knee angle position. A statistically significant between-leg difference in experimentally-measured maximal isometric strength was found at 60° and 90°, but not 15° or 45°, of knee flexion. The musculoskeletal model matched the between-leg differences observed in experimental knee flexion moments at 15° and 45° but did not well estimate between-leg differences with a more flexed knee, particularly at 90°. Further, the knee flexor synergists could not physiologically compensate for weakness in deep knee flexion. These results suggest additional factors other than knee flexor muscle morphology play a role in knee flexion weakness following anterior cruciate ligament reconstruction with a distal semitendinosus tendon graft and thus more work at neural and microscopic levels is required for informing treatment and rehabilitation in this demographic.
Recent studies suggest region‐specific metabolic activity in hamstring muscles during injury prevention exercises, but the neural representation of this phenomenon is unknown. The aim of this study ...was to examine whether regional differences are evident in the activity of biceps femoris long head (BFlh) and semitendinosus (ST) muscles during two common injury prevention exercises. Twelve male participants without a history of hamstring injury performed the Nordic hamstring exercise (NHE) and stiff‐leg deadlift (SDL) while BFlh and ST activities were recorded with high‐density electromyography (HD‐EMG). Normalized activity was calculated from the distal, middle, and proximal regions in the eccentric phase of each exercise. In NHE, ST overall activity was substantially higher than in BFlh (d = 1.06 ± 0.45), compared to trivial differences between muscles in SDL (d = 0.19 ± 0.34). Regional differences were found in NHE for both muscles, with different proximal‐distal patterns: The distal region showed the lowest activity level in ST (regional differences, d range = 0.55‐1.41) but the highest activity level in BFlh (regional differences, d range = 0.38‐1.25). In SDL, regional differences were smaller in both muscles (d range = 0.29‐0.67 and 0.16‐0.63 in ST and BFlh, respectively) than in NHE. The use of HD‐EMG in hamstrings revealed heterogeneous hamstrings activity during typical injury prevention exercises. High‐density EMG might be useful in future studies to provide a comprehensive overview of hamstring muscle activity in other exercises and high‐injury risk tasks.
Background:
Injuries to the hamstring complex most commonly involve the proximal musculotendinous junction of the long head of the biceps femoris (MTJ-BFlh). Nonoperative management of these injuries ...is associated with prolonged rehabilitation and high risk of recurrence. To our knowledge, the surgical management of acute MTJ-BFlh injuries has not been previously reported.
Hypothesis:
Surgical repair of acute MTJ-BFlh injuries enables return to sporting activity with low risk of recurrence.
Study Design:
Case series; Level of evidence, 4.
Methods:
A total of 64 patients (42 male and 22 female) undergoing surgical repair of acute MTJ-BFlh injuries were included. Predefined outcomes were recorded at regular intervals after surgery. Mean follow-up time after surgery was 29.2 months (range, 24.0-37.1 months).
Results:
All study patients returned to their preinjury levels of sporting activity. Mean ± SD time from surgical intervention to return to sporting activity was 13.4 ± 5.1 weeks. Three patients had reinjury at the operative site: 1 (1.6%) with MTJ-BFlh injury and 2 (3.2%) with myofascial tears. At 3 months after surgery, patients had improved mean passive straight-leg raise (72.0° ± 11.4° vs 24.1° ± 6.8°; P < .001); increased mean isometric hamstring muscle strength at 0° (84.5 % ± 10.4% vs 25.9% ± 8.9%; P < .001), 15° (89.5% ± 7.3% vs 41.2% ± 9.7%; P < .001), and 45° (93.9% ± 5.1% vs 63.4% ± 7.6%; P < .001); higher mean Lower Extremity Functional Scale scores (71.5 ± 5.0 vs 29.8 ± 6.3; P < .001); and improved mean Marx activity rating scores (9.8 ± 2.2 vs 3.8 ± 1.9; P < .001), as compared with preoperative scores. High patient satisfaction and functional outcome scores were maintained at 1 and 2 years after surgery.
Conclusion:
Surgical repair of acute MTJ-BFlh injuries enables return to preinjury level of sporting function with low risk of recurrence at short-term follow-up.
To determine which strength training exercises selectively activate the biceps femoris long head (BF
) muscle.
We recruited 24 recreationally active men for this two-part observational study
Part 1: ...We explored the amplitudes and the ratios of lateral (BF) to medial hamstring (MH) normalised electromyography (nEMG) during the concentric and eccentric phases of 10 common strength training exercises. Part 2: We used functional MRI (fMRI) to determine the spatial patterns of hamstring activation during two exercises which (1) most selectively and (2) least selectively activated the BF in part 1.
Eccentrically, the largest BF/MH nEMG ratio occurred in the 45° hip-extension exercise; the lowest was in the Nordic hamstring (Nordic) and bent-knee bridge exercises. Concentrically, the highest BF/MH nEMG ratio occurred during the lunge and 45° hip extension; the lowest was during the leg curl and bent-knee bridge. fMRI revealed a greater BF
to semitendinosus activation ratio in the 45° hip extension than the Nordic (p<0.001). The T2 increase after hip extension for BF
, semitendinosus and semimembranosus muscles was greater than that for BF
(p<0.001). During the Nordic, the T2 increase was greater for the semitendinosus than for the other hamstring muscles (p≤0.002).
We highlight the heterogeneity of hamstring activation patterns in different tasks. Hip-extension exercise selectively activates the long hamstrings, and the Nordic exercise preferentially recruits the semitendinosus. These findings have implications for strategies to prevent hamstring injury as well as potentially for clinicians targeting specific hamstring components for treatment (mechanotherapy).
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