The effect of external focus versus internal focus instruction on jump-landing biomechanics in healthy females

CONTEXT

Different forms of instruction have contributed to favorable results in injury interventions. External focus (EF) instruction may be superior to internal focus (IF) instruction.

OBJECTIVE

To investigate the difference in landing biomechanics between participants who received EF versus IF instruction and a control. A secondary aim was to evaluate participant perceptions of focus of attention.

DESIGN

Randomized controlled trial.

SETTING

Laboratory.

PATIENTS OR OTHER PARTICIPANTS

Forty-one healthy females. EF: N=14; 23.0±2.9yrs; 1.69±0.07m; 64.0±6.8kg; IF: N=15; 22.9±3.2yrs;1.66±0.08m;66.2±12.4kg; Control: N=12; ±2.9yrs; 1.67±0.11m; 74.3±15.1kg.

MAIN OUTCOME MEASURES

Participants scoring ≥ five on the LESS and were allocated into EF, IF or control groups. Knee and hip flexion and abduction were collected pre- and post-intervention during five drop vertical jumps. For the intervention, each group was provided separate instructions. In-between the intervention jumps, participants answered: "What strategy were you focusing on when completing the previous jump-landing trials?". Post-intervention minus pre-intervention change scores were calculated and separate 1-way ANOVAs assessed differences in the dependent variables.

RESULTS

EF had a greater change in hip and knee flexion angles versus control. There was no significant difference between EF and IF for any variables. There were no significant differences in frontal plane variables. In the EF group, 71.4% were "aligned". In the IF group, 80% of the were "aligned". In the CONT group, 50% were "aligned".

CONCLUSIONS

EF instruction may not produce immediate changes in movement compared to IF instruction. Hip and knee flexion were greater in the EF group compared to the control group but was not better than the IF group. Clinicians should provide instruction to patients, but the mode of instruction may not be as critical to see positive biomechanical changes. Patients may not always focus on the instruction being given, therefore the relationship between instruction and patient experience should be further explored.

Effects of 12-week cadence retraining on impact peak, load rates and lower extremity biomechanics in running

Background

Excessive impact peak forces and vertical load rates are associated with running injuries and have been targeted in gait retraining studies. This study aimed to determine the effects of 12-week cadence retraining on impact peak, vertical load rates and lower extremity biomechanics during running.

Methods

Twenty-four healthy male recreational runners were randomised into either a 12-week cadence retraining group (n = 12), which included those who ran with a 7.5% increase in preferred cadence, or a control group (n = 12), which included those who ran without any changes in cadence. Kinematics and ground reaction forces were recorded simultaneously to quantify impact force variables and lower extremity kinematics and kinetics.

Results

Significantly decreased impact peak (1.86 ± 0.30 BW vs. 1.67 ± 0.27 BW, P = 0.003), vertical average load rates (91.59 ± 18.91 BW/s vs. 77.31 ± 15.12 BW/s, P = 0.001) and vertical instantaneous load rates (108.8 ± 24.5 BW/s vs. 92.8 ± 18.5 BW/s, P = 0.001) were observed in the cadence retraining group, while no significant differences were observed in the control group. Foot angles (18.27° ± 5.59° vs. 13.74° ± 2.82°, P = 0.003) and vertical velocities of the centre of gravity (CoG) (0.706 ± 0.115 m/s vs. 0.652 ± 0.091 m/s, P = 0.002) significantly decreased in the cadence retraining group at initial contact, but not in the control group. In addition, vertical excursions of the CoG (0.077 ± 0.01 m vs. 0.069 ± 0.008 m, P = 0.002) and peak knee flexion angles (38.6° ± 5.0° vs. 36.5° ± 5.5°, P < 0.001) significantly decreased whilst lower extremity stiffness significantly increased (34.34 ± 7.08 kN/m vs. 38.61 ± 6.51 kN/m, P = 0.048) in the cadence retraining group. However, no significant differences were observed for those variables in the control group.

Conclusion

Twelve-week cadence retraining significantly increased the cadence of the cadence retraining group by 5.7%. This increased cadence effectively reduced impact peak and vertical average/instantaneous load rates. Given the close relationship between impact force variables and running injuries, increasing the cadence as a retraining method may potentially reduce the risk of impact-related running injuries.

Passive Muscular Insufficiency: The Etiology of Gastrocnemius Equinus

The current understanding is that gastrocnemius equinus is caused by a pathologic tightening of the muscle leading to decreased ankle joint dorsiflexion. However, an alternative hypothesis is that it is a normal limitation of available muscle length. Passive muscular insufficiency of the gastrocnemius muscle acts on a pathologic foot, which is poorly prepared to accept the forces from the gastrocnemius-soleus complex. In this manner, a normal gastrocnemius muscle exerts abnormal forces across the foot. This alternative hypothesis leads to a different interpretation of the current research literature and a potential new area of biomechanical research.

A 6-week warm-up injury prevention programme results in minimal biomechanical changes during jump landings: a randomized controlled trial

PURPOSE

To examine the extent to which an ACL injury prevention programme modifies lower extremity biomechanics during single- and double-leg landing tasks in both the sagittal and frontal plane. It was hypothesized that the training programme would elicit improvements in lower extremity biomechanics, but that these improvements would be greater during a double-leg sagittal plane landing task than tasks performed on a single leg or in the frontal plane.

METHODS

Ninety-seven competitive multi-directional sport athletes that competed at the middle- or high-school level were cluster randomized into intervention (n = 48, age = 15.4 ± 1.0 years, height = 1.7 ± 0.07 m, mass = 59.9 ± 11.0 kg) and control (n = 49, age = 15.7 ± 1.6 years, height = 1.7 ± 0.06 m, mass = 60.4 ± 7.7 kg) groups. The intervention group participated in an established 6-week warm-up-based ACL injury prevention programme. Three-dimensional biomechanical analyses of a double- (SAG-DL) and single-leg (SAG-SL) sagittal, and double- (FRONT-DL) and single-leg (FRONT-SL) frontal plane jump landing tasks were tested before and after the intervention. Peak angles, excursions, and external joint moments were analysed for group differences using 2 (group) × 4 (task) repeated measures MANOVA models of delta scores (post-pre-test value) (α < 0.05).

RESULTS

Relative to the control group, no significant biomechanical changes were identified in the intervention group for any of the tasks (n.s.). However, a group by task interaction was identified for knee abduction (λ = 0.80, p = 0.02), such that participants in the intervention group showed relative decreases in knee abduction moments during the SAG-DL compared to the SAG-SL (p = 0.005; d = 0.45, CI = 0.04-0.85) task.

CONCLUSION

A 6-week warm-up-based ACL injury prevention programme resulted in no significant biomechanical changes during a variety of multi-directional jump landings. Clinically, future prevention programmes should provide a greater training stimulus (intensity, volume), more specificity to tasks associated with the mechanism of ACL injury (single-leg, non-sagittal plane jump landings), and longer programme duration (> 6 weeks) to elicit meaningful biomechanical changes.

LEVEL OF EVIDENCE

I.

Quantification of functional brace forces for posterior cruciate ligament injuries on the knee joint: an in vivo investigation

PURPOSE

Counteracting posterior translation of the tibia with an anterior force on the posterior proximal tibia has been demonstrated clinically to improve posterior knee laxity following posterior cruciate ligament (PCL) injury. This study quantified forces applied to the posterior proximal tibia by two knee braces designed for treatment of PCL injuries.

METHODS

The forces applied by two knee braces to the posterior proximal tibia and in vivo three-dimensional knee kinematics of six adult, male, healthy volunteer subjects (mean ± standard deviation: height, 182.5 ± 5.2 cm; body mass, 83.2 ± 9.3 kg; body mass index, 24.9 ± 1.5 kg/m(2); age, 25.8 ± 2.9 years) were measured using a custom pressure mapping technique and traditional surface marker motion capture techniques, while subjects performed three functional activities. The activities included seated unloaded knee flexion, squatting, and stair descent in a new generation dynamic force (DF) PCL brace and a static force (SF) PCL brace.

RESULTS

During unloaded flexion at the lowest force level setting, the force applied by the DF brace increased as a function of flexion angle (slope = 0.7 N/°; p < 0.001) compared to the SF brace effect. Force applied by the SF brace did not significantly change as a function of flexion angle (slope = 0.0 N/°; n.s.). By 45° of flexion, the average force applied by the DF brace (48.1 N) was significantly larger (p < 0.001) than the average force applied by the SF brace (25.0 N). The difference in force continued to increase as flexion angle increased. During stair descent, average force (mean ± standard deviation) at toe off was significantly higher (p = 0.013) for the DF brace (78.7 ± 21.6 N) than the SF brace (37.3 ± 7.2 N). Similar trends were observed for squatting and for the higher force level settings.

CONCLUSIONS

The DF brace applied forces to the posterior proximal tibia that dynamically increased with increased flexion angle. Additionally, the DF brace applied significantly larger forces at higher flexion angles compared to the SF brace where the PCL is known to experience larger in situ forces. Clinical studies are necessary to determine whether the loading characteristics of the DF brace, which more closely replicated the in situ loading profile of the native PCL, results in long-term improved posterior knee laxity following PCL injury.

LEVEL OF EVIDENCE

II.