Gymnastik- och idrottshögskolan, GIH

BACKGROUND: Hamstring strain is a common injury in sprinters and jumpers, and therefore time to return to sport and secondary prevention become of particular concern.

OBJECTIVE: To compare the effectiveness of two rehabilitation protocols after acute hamstring injury in Swedish elite sprinters and jumpers by evaluating time needed to return to full participation in the training process.

STUDY DESIGN: Prospective randomised comparison of two rehabilitation protocols.

METHODS: Fifty-six Swedish elite sprinters and jumpers with acute hamstring injury, verified by MRI, were randomly assigned to one of two rehabilitation protocols. Twenty-eight athletes were assigned to a protocol emphasising lengthening exercises, L-protocol, and 28 athletes to a protocol consisting of conventional exercises, C-protocol. The outcome measure was the number of days to return to full training. Re-injuries were registered during a period of 12 months after return.

RESULTS: Time to return was significantly shorter for the athletes in the L-protocol, mean 49 days (1SD±26, range 18-107 days), compared with the C-protocol, mean 86 days (1SD±34, range 26-140 days). Irrespective of protocol, hamstring injuries where the proximal free tendon was involved took a significantly longer time to return than injuries that did not involve the free tendon, L-protocol: mean 73 vs 31 days and C-protocol: mean 116 vs 63 days, respectively. Two reinjuries were registered, both in the C-protocol.

CONCLUSIONS: A rehabilitation protocol emphasising lengthening type of exercises is more effective than a protocol containing conventional exercises in promoting time to return in Swedish elite sprinters and jumpers.

The purpose of the present study was to investigate the pattern of trunk muscle activation and intra-abdominal pressure (IAP) in a somewhat modified version of the clean and jerk lift. Nine healthy physically active male amateurs performed the exercise with a 30-kg barbell. Muscle activity was registered with electromyography from transversus abdominis (TrA) and obliquus internus (OI) using intramuscular electrodes and from rectus abdominis (RA) and erector spinae (ES) with surface electrodes. IAP was recorded with a nasogastric catheter. Measurements were made in various static positions throughout the lift and in the transitional phases separating them, both during lifting and lowering. The results demonstrated that the innermost abdominal muscle, TrA, showed increased activation levels in the two highest positions, whereas ES was most active, together with the highest IAP, in the lowest position. OI and RA showed generally little activation and no obvious trend throughout the lift. The results strengthen the view of a contributing role of TrA to the upright control of the trunk and indicate that the clean and jerk lift might constitute a whole-body exercise, still targeting the TrA muscle, in late-stage rehabilitation, especially for athletes during return to sports.

BACKGROUND: Hamstring injury is the single most common injury in European professional football and, therefore, time to return and secondary prevention are of particular concern.

OBJECTIVE: To compare the effectiveness of two rehabilitation protocols after acute hamstring injury in Swedish elite football players by evaluating time needed to return to full participation in football team-training and availability for match selection.

STUDY DESIGN: Prospective randomised comparison of two rehabilitation protocols.

METHODS: Seventy-five football players with an acute hamstring injury, verified by MRI, were randomly assigned to one of two rehabilitation protocols. Thirty-seven players were assigned to a protocol emphasising lengthening exercises, L-protocol and 38 players to a protocol consisting of conventional exercises, C-protocol. The outcome measure was the number of days to return to full-team training and availability for match selection. Reinjuries were registered during a period of 12 months after return.

RESULTS: Time to return was significantly shorter for the players in the L-protocol, mean 28 days (1SD±15, range 8-58 days), compared with the C-protocol, mean 51 days (1SD±21, range 12-94 days). Irrespective of protocol, stretching-type of hamstring injury took significantly longer time to return than sprinting-type, L-protocol: mean 43 vs 23 days and C-protocol: mean 74 vs 41 days, respectively. The L-protocol was significantly more effective than the C-protocol in both injury types. One reinjury was registered, in the C-protocol.

CONCLUSIONS: A rehabilitation protocol emphasising lengthening type of exercises is more effective than a protocol containing conventional exercises in promoting time to return in Swedish elite football.

Abdominal muscle recruitment strategies in response to a postural perturbation contradict the theory that the deeper abdominal muscles are always recruited in advance of the more superficial muscles. The purpose of this study was to determine whether such contrasting muscle recruitment patterns are due to the postural task or the predictability of a postural task. Participants performed an arm raise task as well as an unpredictable and a predictable balance perturbation task (i.e. support-surface translation) while intramuscular electromyographic (EMG) recordings were obtained from the deep [transversus abdominis (TrA)] and superficial [obliquus externus (OE)] abdominal muscles. The abdominal muscle recruitment order was dependent on the postural task but not on the predictability of a postural perturbation. Whereas arm raises elicited similar EMG onset latencies in TrA and OE, the OE onset latency was 48 ms earlier than the TrA following an unpredictable translation (P = 0.003). The early OE activation persisted when the translation was made predictable to the participant (P = 0.024). These results provide evidence that the abdominal muscle recruitment order varies with the trunk stability requirements specific to each task. Rehabilitation strategies focusing on an early TrA activation to improve postural stability may not be appropriate for all everyday tasks.

PURPOSE:

An initial step in the understanding of Achilles tendon dynamics is to investigate the effects of passive motion, thereby minimising muscle activation and reducing internal joint forces. Internal tendon dynamics during passive ankle joint motion have direct implications for clinical rehabilitation protocols after Achilles tendon surgery. The aim of this study was to test the hypothesis that tendon tissue displacement is different in different layers of the Achilles tendon during controlled passive ankle joint movements.

METHODS:

Ultrasound imaging was conducted on the right Achilles tendon of nine healthy recreationally active males. Standardised isokinetic passive dorsi-plantar-flexion movements were performed with a total range of motion of 35°. The tendon was divided into superficial, central and deep layers in the resulting B-mode ultrasound images viewed in the sagittal plane. A block-matching speckle tracking algorithm was applied post-process, with kernels for the measurement of displacement placed in each of the layers.

RESULTS:

The mean (SD) displacement of the Achilles tendon during passive dorsiflexion was 8.4 (1.9) mm in the superficial layer, 9.4 (1.9) mm in the central portion and 10.4 (2.1) mm in the deep layer, respectively. In all cases, the movement of the deep layer of the tendon was greater than that of the superficial one (P < 0.01).

CONCLUSIONS:

These results, achieved in vivo with ultrasonographic speckle tracking, indicated complex dynamic differences in different layers of the Achilles tendon, which could have implications for the understanding of healing processes of tendon pathologies and also of normal tendon function.

Transversus abdominis (TrA) is a multifunctional muscle, being involved in pressure regulation within the abdominal cavity and thereby in direction independent stabilization of the spine and resistance to imposed trunk flexion moments. Indirect evidence suggests a role of TrA also in postural control of the erect human trunk. The main purpose here was to investigate if the magnitude of TrA activation is related to postural demand. Eleven healthy males performed seven different symmetrical static bilateral arm positions holding 3 kg in each hand. The arm positions were selected to systematically vary the height of the centre of mass (COM) keeping imposed moments constant and vice versa. EMG was recorded bilaterally with fine-wire intramuscular electrodes from TrA and obliquus internus (OI) and with surface electrodes from rectus abdominis (RA) and erector spinae (ES). Intra-abdominal pressure (IAP) was measured via a pressure transducer in the gastric ventricle. TrA was the only muscle that displayed activation co-varying with the vertical position of the COM. Further, TrA activation increased, together with IAP and ES activation, with imposed flexion moment, i.e. with arms extended horizontally forward. In contrast to OI, RA and ES, TrA activation was independent of the direction of the imposed moment (arms held inclined forward or backward). In conclusion, TrA activation level is uniquely associated with increased postural demand caused by elevated COM. Also, TrA appears to assist in counteracting trunk flexion via increased IAP, and contribute to general spine stabilization when the trunk is exposed to moderate flexion and extension moments.

For older people balance control in standing is critical for performance of activities of daily living without falling. The aims were to investigate reliability of quantification of the usage of the two balance mechanisms M₁ ‘moving the centre of pressure’ and M₂ ‘segment acceleration’ and also to compare calculation methods based on a combination of kinetic (K) and kinematic (Km) data, (K–Km), or Km data only concerning M₂. For this purpose nine physically fit persons aged 70–78 years were tested in narrow and single-leg standing. Data were collected by a 7-camera motion capture system and two force plates. Repeated measure ANOVA and Tukey's post hoc tests were used to detect differences between the standing tasks. Reliability was estimated by ICCs, standard error of measurement including its 95% CI, and minimal detectable change, whereas Pearson's correlation coefficient was used to investigate agreement between the two calculation methods. The results indicated that for the tasks investigated, M₁ and M₂ can be measured with acceptable inter- and intrasession reliability, and that both Km and K–Km based calculations may be useful for M₂, although Km data may give slightly lower values. The proportional M₁:M₂ usage was approximately 9:1, in both anterio-posterior (AP) and medio-lateral (ML) directions for narrow standing, and about 2:1 in the AP and of 1:2 in the ML direction in single-leg standing, respectively. In conclusion, the tested measurements and calculations appear to constitute a reliable way of quantifying one important aspect of balance capacity in fit older people.

 Neural activation is generally lower during maximal voluntary lengthening compared with shortening and isometric muscle actions, but the mechanisms underlying these differences are unclear. In maximal voluntary isometric actions, reduced Ia-afferent input induced by prolonged tendon vibration has been shown to impair neural activation and strength.

PURPOSE: This study aimed to investigate whether reducing Ia-afferent input influences neural activation in maximal voluntary dynamic muscle actions and, if so, whether it affects shortening and lengthening muscle actions differently.

METHODS: Eight women participated in three familiarization sessions and two randomly ordered experiments. In one experiment, 30-min vibration at 100 Hz was applied to the Achilles tendon to decrease Ia-afferent input as measured by the H-reflex. In the control experiment, rest substituted the vibration. Root mean square EMG from plantar and dorsiflexor muscles and plantar flexor strength were measured during maximal voluntary plantar flexor shortening and lengthening actions (20°·s(-1)) before and after vibration and rest, respectively. Soleus H-reflexes and M-waves were elicited before each set of strength tests.

RESULTS: The vibration caused a decrease in H-reflex amplitude by, on the average, 33%, but root mean square EMG and plantar flexor strength remained largely unaffected in both action types.

CONCLUSIONS: The findings suggest that Ia-afferent input may not substantially contribute to maximal voluntary dynamic muscle strength of the plantar flexor muscles, as tested here, and thus, the results do not support the notion that Ia-afferent excitation would contribute differently to neural activation in maximal voluntary lengthening and shortening muscle actions.

PURPOSE: The aim was to introduce and evaluate the reliability and validity of an active hamstring flexibility test as a complement to common clinical examination when determining safe return to sport after hamstring injury.

METHODS: Eleven healthy subjects (28 years) were tested on repeated occasions, and 11 athletes (21 years) with MRI-verified acute hamstring strain were tested when common clinical examination revealed no signs of remaining injury, i.e. there was no differences between the legs in palpation pain, manual strength tests, and passive straight leg raise. Flexibility, i.e. highest range of motion of three consecutive trials, was calculated from electrogoniometer data during active ballistic hip flexions and conventional passive slow hip-flexions in a supine position. A VAS-scale (0-100) was used to estimate experience of insecurity during active tests.

RESULTS: No significant test-retest differences were observed. Intra-class correlation coefficients ranged 0.94-0.99 and coefficients of variation 1.52-4.53%. Active flexibility was greater (23%) than passive flexibility. In the athletes, the injured leg showed smaller (8%) active, but not passive, flexibility than the uninjured leg. Average insecurity estimation was 52 (range 28-98) for the injured and 0 for the uninjured leg, respectively.

CONCLUSION: The new test showed high reliability and construct validity; furthermore, it seems to be sensitive enough to detect differences both in active flexibility and in insecurity after acute hamstring strains at a point in time when the commonly used clinical examination fails to reveal injury signs. Thus, the test could be a complement to the common clinical examination before the final decision to return to sport is made.