A high incidence of injury among male university student rugby players requires urgent injury prevention strategies

OBJECTIVES

Determine the epidemiology and clinical characteristics of training and match injuries in university student rugby players over a two-season period.

DESIGN

Prospective cohort.

SETTING

Varsity Cup (VC) and Young Guns (YG) rugby tournaments (2018 and 2019).

PARTICIPANTS

171 male university student rugby players.

MAIN OUTCOME MEASURES

For time-loss injuries: injury incidence (injuries per 1000 player-hours), injured player proportion (% of injured players) and the frequency (n, %) of injury characteristics (new or recurrent, anatomical region, body area, severity.

RESULTS

The injury incidence was 2.4 per 1000 player-hours for training injuries and 131.1 per 1000 player-hours for match injuries. The overall injured player proportion was 59.6%. New injuries (83.9%) were more frequent than recurrent injuries. Most injuries occurred in the lower limb involving muscle/tendon (56.7%) and ligament/joint capsule (27.2%). The shoulder (19.6%) and ankle (15.7%) were the most common body areas of injury during matches and training, respectively.

CONCLUSIONS

There was a high injured player proportion and match injury incidence among university student rugby players. Most injuries were new. Lower limb injuries were most common in training whereas upper limb injuries were most common in matches. These findings highlight the need to prioritise future injury prevention among university student rugby players.

Characterising coordination strategies during initial acceleration in sprinters ranging from highly trained to world class

Identifying coordination strategies used by sprinters and features that differentiate these strategies will aid in understanding different technical approaches to initial sprint acceleration. Moreover, multiple effective coordination strategies may be available to athletes of similar ability, which typical group-based analyses may mask. This study aimed to identify sub-groups of sprinters based on thigh-thigh and shank-foot coordination during initial acceleration, and assess sprint performance across different combinations of coordination strategies. Angular kinematics were obtained from 21 sprinters, and coordination determined using vector coding methods, with step 1 and steps 2-4 separated for analysis. Performance was assessed using metrics derived from velocity-time profiles. Using hierarchical cluster analysis, three distinct coordination strategies were identified from thigh-thigh and shank-foot coordination in step 1 and two strategies in steps 2-4. Coordination strategies primarily differed around early flight thigh-thigh coordination and early stance shank-foot coordination in step 1, while timing of reversals in thigh rotation characterised differences in later steps. Higher performers tended to have greater lead thigh and foot dominance in step 1 and early swing thigh retraction in steps 2-4. The novel application of cluster analysis to coordination provides new insights into initial acceleration technique in sprinters, with potential considerations for training and performance.

Biomechanics in Africa: current state and potential for growth

The potential of biomechanics for improving human health and performance is well established in many parts of the world. However, across most of Africa, biomechanics remains relatively underdeveloped. The discussion around biomechanics in the continent has increased in recent times and young African scientists are pursuing career opportunities in biomechanics-related fields within Africa and in other parts of the world. New institutions and programmes that focus on biomechanics teaching and research are also starting up around the continent. The advent of the National Biomechanics Day event, formation of the first formal biomechanics society in South Africa, along with many collaborations with relevant stakeholder organizations around the world underpin the expansion of biomechanics in Africa. This article aims to summarize the current state and describe aspirations for the future of biomechanics in Africa.

Inter- and intra-limb coordination during initial sprint acceleration

In complex movements, centre of mass translation is achieved through effective joint and segment rotations. Understanding segment organisation and coordination is therefore paramount to understanding technique. This study sought to comprehensively describe inter- and intra-limb coordination and assess step-to-step changes and between-individual variation in coordination during initial sprint acceleration. Twenty-one highly trained to world class male (100 m PB 9.89-11.15 s) and female (100 m PB:11.46-12.14 s) sprinters completed sprint trials of at least 20 m from which sagittal plane kinematics were obtained for the first four steps using inertial measurement units (200 Hz). Thigh-thigh, trunk-shank and shank-foot coordination was assessed using a modified vector coding and segment dominancy approach. Common coordination patterns emerged for all segment couplings across sexes and performance levels, suggesting strong task constraints. Between-individual variation in inter-limb thigh coordination was highest in early flight, while trunk-shank and shank-foot variation was highest in late flight, with a second peak in late stance for the trunk-shank coupling. There were clear step-to-step changes in coordination, with step 1 being distinctly different to subsequent steps. The results demonstrate that inter-limb coordination is primarily anti-phase and trailing leg dominant while ankle motion in flight and late stance appears to be primarily driven by the foot.

1st Conference of the South African Society of Biomechanics

Abstracts for the Conference of the South African Society of Biomechanics

Objective classification of countermovement jump force-time curve modality: within athlete-consistency and associations with jump performance

Force-time curves produced during a countermovement jump (CMJ) have traditionally been classified by visual observation as either unimodal (one concentric phase peak) or bimodal (two peaks). The association between CMJ modality and jump performance remains unclear and future studies may benefit from standardising and expanding modality classification. This study described a numerical method based on the timing and relative magnitude of concentric force-time curve prominences. Adult male elite rugby union players (n = 214) performed six CMJs on a force-instrumented treadmill and an algorithm using turning-point logic was applied to categorise jumps and define modality sub-groups. A sensitivity analysis demonstrated that the minimum prominence threshold (MPT) affected categorisation, as the proportion of bimodal jumps decreased with each 1% increase in MPT. Within-athlete consistency was also affected; between 43% and 63% of participants were consistently categorised as bimodal or unimodal depending on the selected MPT. Modified reactive strength index (RSImod), but not jump height or take-off momentum, was greater in unimodal jumps. Take-off momentum and RSImod were greater in subcategories where maximum force occurred early in the concentric phase. Future research should implement objective classification methods to enhance transparency and comparability and consider subcategories to investigate CMJ force production strategies.

Ratio of forces during sprint acceleration: A comparison of different calculation methods

The orientation of the ground reaction force (GRF) vector is a key determinant of human sprint acceleration performance and has been described using ratio of forces (RF) which quantifies the ratio of the antero-posterior component to the resultant GRF. Different methods have previously been used to calculate step-averaged RF, and this study therefore aimed to compare the effects of three calculation methods on two key "technical" ability measures: decline in ratio of forces (D_RF) and theoretical maximal RF at null velocity (RF₀). Twenty-four male sprinters completed maximal effort 60 m sprints from block and standing starts on a fully instrumented track (force platforms in series). RF-horizontal velocity profiles were determined from the measured GRFs over the entire acceleration phase using three different calculation methods for obtaining an RF value for each step: A) the mean of instantaneous RF during stance, B) the step-averaged antero-posterior component divided by the step-averaged resultant GRF, C) the step-averaged antero-posterior component divided by the resultant of the step-averaged antero-posterior and vertical components. Method A led to significantly greater RF₀ and shallower D_RF slopes than Methods B and C. These differences were very large (Effect size Cohen's d = 2.06 - 4.04) and varied between individuals due to differences in the GRF profiles, particularly during late stance as the acceleration phase progressed. Method B provides RF values which most closely approximate the mechanical reality of step averaged accelerations progressively approaching zero and it is recommended for future analyses although it should be considered a ratio of impulses.

Biomechanics without Borders: Teaching Biomechanics in Brazil and South Africa

The "Biomechanics without Borders: Teaching Biomechanics in Brazil and South Africa" involved academics from different countries combining efforts to improve remote education. In addition to the live discussions, the event resulted in the availability of online content to help academic staffs improve teaching strategies in the field of human movement sciences.

Wearable resistance sprint running is superior to training with no load for retaining performance in pre-season training for rugby athletes

This study determined the effects of a six-week lower-limb wearable resistance training (WRT) intervention on sprint running time, velocity, and horizontal force-velocity mechanical variables. Twenty-two collegiate/semi-professional rugby athletes completed pre- and post-intervention testing of three maximal effort 30 m sprints. A radar device was used to measure sprint running velocity from which horizontal force-velocity mechanical profiling variables were calculated. All athletes completed two dedicated sprint training sessions a week for six-weeks during pre-season. The intervention (wearable resistance, WR) group completed the sessions with 1% body mass load attached to the left and right shanks (i.e. 0.50% body mass load on each limb), whilst the control group completed the same sessions unloaded. For the control group, all variables were found to detrain significantly (p ≤ 0.05) over the training period with large detraining effects (ES > 0.80) for theoretical maximal horizontal force, slope of the force-velocity profile, maximal ratio of force, index of force application, 5 and 10 m times. For the WR group, there were no significant changes to any recorded variables (all p >  0.05) and all effects of training were trivial or small (ES < 0.50). After adjustment for baseline differences, significant between group differences were found for all variables (large effects, ES > 0.80) except theoretical maximal velocity, 30 m time, and maximal velocity. The addition of light wearable resistance to sprint training during a six-week pre-season block enables the maintenance of sprint performance and mechanical output qualities that otherwise would detrain due to inadequate training frequencies.

Team illness prevention strategy (TIPS) is associated with a 59% reduction in acute illness during the Super Rugby tournament: a control–intervention study over 7 seasons involving 126 850 player days

Objectives

To determine whether a team illness prevention strategy (TIPS) would reduce the incidence of acute illness during the Super Rugby tournament.

Methods

We studied 1340 male professional rugby union player seasons from six South African teams that participated in the Super Rugby tournament (2010–2016). Medical staff recorded all illnesses daily (126 850 player days) in a 3-year control (C: 2010–2012; 47 553 player days) and a 4-year intervention (I: 2013–2016; 79 297 player days) period. A five-element TIPS was implemented in the I period, following agreement by consensus. Incidence rate (IR: per 1000 player days; 95% CI) of all acute illnesses, illness by main organ system, infectious illness and illness burden (days lost due to illness per 1000 player days) were compared between C and I period.

Results

The IR of acute illness was significantly lower in the I (5.5: 4.7 to 6.4) versus the C period (13.2: 9.7 to 18.0) (p<0.001). The IR of respiratory (C=8.6: 6.3 to 11.7; I=3.8: 3.3 to 4.3) (p<0.0001), digestive (C=2.5: 1.8 to 3.6; I=1.1: 0.8 to 1.4) (p<0.001), skin and subcutaneous tissue illness (C=0.7: 0.4 to 1.4; I=0.3: 0.2 to 0.5) (p=0.0238), all infections (C=8.4: 5.9 to 11.9; I=4.3: 3.7 to 4.9) (p<0.001) and illness burden (C=9.2: 6.8 to 12.5; I=5.7: 4.1 to 7.8) (p=0.0314) were significantly lower in the I versus the C period.

Conclusion

A TIPS during the Super Rugby tournament was associated with a lower incidence of all acute illnesses (59%), infectious illness (49%) and illness burden (39%). Our findings may have important clinical implications for other travelling team sport settings.

Match injury incidence during the Super Rugby tournament is high: a prospective cohort study over five seasons involving 93 641 player-hours

Objectives

To determine the incidence and nature of injuries in the Super Rugby tournament over a 5-year period.

Methods

482 male professional rugby union players from six South African teams participating in the Super Rugby tournament were studied (1020 player-seasons). Medical staff of participating teams (2012–2016 tournaments) recorded all time loss injuries (total injuries and match injuries) and exposure hours (93 641 total playing hours; 8032 match hours). Injury incidence, injured player proportion, severity (time lost), anatomical location, tissue type and activity/phase during which injury occurred are reported.

Results

The overall incidence of match injuries (per 1000 player-hours; 95% CI) for each year was as follows: 2012 (83.3; 69.4–99.2); 2013 (115.1; 98.7–133.5); 2014 (95.9; 80.8–113.1), 2015 (112.3; 96.6–129.9) and 2016 (93.2; 79.9–107.9). The injured player proportion for each year was as follows: 2012 (54.6%); 2013 (49.4%); 2014 (52.0%); 2015 (50.0%); and 2016 (39.8%). The thigh, knee, head/face and shoulder/clavicle are the most frequently injured locations, and muscle/tendon and joint/ligament injuries account for the majority of injuries. Most injuries (79%) occur in contact situations, in particular during a tackle (54%).

Conclusion

The incidence of match injuries and the injured player proportion in South African teams competing in the Super Rugby tournament is high. Match injury incidence is consistently higher than previously reported for senior male rugby players at elite/professional level. Targeted risk management strategies are therefore needed in the Super Rugby tournament to manage risk of injury.

The influence of foot position on scrum kinetics during machine scrummaging

The purpose of this study was to investigate the effect of variations in the alignment of the feet on scrum kinetics during machine scrummaging. Twenty nine rugby forwards from amateur-level teams completed maximal scrum efforts against an instrumented scrum machine, with the feet in parallel and non-parallel positions. Three-dimensional forces, the moment about the vertical axis and sagittal plane joint angles were measured during the sustained pushing phase. There was a decrease in the magnitude of the resultant force and compression force in both of the non-parallel conditions compared to parallel and larger compression forces were associated with more extended hip and knee angles. Scrummaging with the left foot forward resulted in the lateral force being directed more towards the left and the turning moment becoming more clockwise. These directional changes were reversed when scrummaging with the right foot forward. Scrummaging with the right foot positioned ahead of the left may serve to counteract the natural clockwise wheel of the live scrum and could be used to achieve an anti-clockwise rotation of the scrum for tactical reasons. However, this would be associated with lower resultant forces and a greater lateral shear force component directed towards the right.

Incidence of injury and illness in South African professional male soccer players: a prospective cohort study

BACKGROUND

Medical illnesses and sports-related injuries both have an effect on athlete health and performance. Epidemiology of injury and illness has been extensively researched during international soccer tournaments and the European soccer season. Reports on injury location and severity differ across geographical regions, and there is limited information on injury epidemiology in African soccer leagues. No studies have investigated the illness burden in soccer in Africa.

METHODS

This was a prospective cohort study involving two soccer teams over the 10-month duration of the 2015/16 Premier Soccer League in South Africa. Team medical staff recorded daily soccer exposure, illness and injuries. Team-based match and training exposure was calculated and used to determine injury and illness incidence and burden over the soccer season.

RESULTS

Overall injury incidence was 2.2/1000 hours, with match injury incidence of 24.8/1000 hours and training injury incidence of 0.9/1000 hours. Time loss injuries accounted for 33 of the 44 injuries recorded. The most common time loss injury location was the knee (14 injuries, 42%). There were 7 minimal, 4 mild, 12 moderate and 10 severe injuries. Sprain/ligament injury (8 injuries) was the most common type, followed by meniscus/cartilage injury (7 injuries). Eleven illnesses were reported during the season, with an incidence of 0.7/1000 player days, and most were minimal in severity (8/11). The illness burden was 1.7/1000 player days. The respiratory (46%) and gastrointestinal (36%) systems were most commonly affected.

CONCLUSIONS

The incidence of injury was comparable with data reported internationally and mirrors the increased risk of injury during matches versus training. The nature of injury differed in that the knee was more frequently affected than the ankle or thigh, joint injuries were more common than muscle injuries, and there was a larger proportion of severe injuries. The illness burden was very low.

Relationship of hyperthermia-induced hemolysis of human erythrocytes to the thermal denaturation of membrane proteins

Hemolysis of human erythrocytes as a function of time of exposure to 47.4-54.5 degrees C was measured and correlated to thermal transitions in the membranes of intact erythrocytes as determined by differential scanning calorimetry (DSC). Curves of hemoglobin leakage (a measure of hemolysis) as a function of time have a shoulder region exhibiting no leakage, indicative of the ability to accumulate sublethal damage (i.e., damage not sufficient to cause lysis), followed by a region of leakage approximating pseudo-first-order kinetics. Inverse leakage rates (Do) of 330-21 min were obtained from 47.4-54.5 degrees C, respectively. A relatively high activation energy of 304 +/- 22 kJ/mol was obtained for leakage, eliminating the involvement of metabolic processes but implicating a transition as the rate-limiting step. Membrane protein involvement was suggested by the very low rate (10(-2) of the rate from erythrocytes) and low activation energy (50 +/- 49 kJ/mol) of hemoglobin leakage from liposomes containing no membrane protein. A model was developed that predicts a transition temperature (Tm) for the critical target (rate-limiting step) of 60 degrees C when measured at a scan rate of 1 K/min. DSC scans were obtained from intact erythrocytes and a procedure developed to fit and remove the transition for hemoglobin denaturation which dominated the scan. Three transitions remained (transitions A, B, and C) with Tm values of 50.0, 56.8, and 63.8 degrees C, respectively. These correspond to, but occur at slightly different temperatures than, the A, B, and C transitions of isolated erythrocyte membranes in the same salt solution (Tm = 49.5, 53-58, and 65.5 degrees C, respectively). In addition, the relative enthalpies of the three transitions differ between isolated membranes and erythrocytes, suggestive of membrane alterations occurring during isolation. Thus, all analyses were conducted on DSC scans of intact erythrocytes. The B transition is very broad and probably consists of several transitions. An inflection, which is seen as a distinct peak (transition B3) in fourth-derivative curves, occurs at 60.8 degrees C and correlates well with the predicted Tm of the critical target. Ethanol (2.2%) lowers the Tm of B3 by 4.0-4.5 K, close to the shift of 3.3 K predicted from its effect on hemolysis. Glycerol (10%) has very little effect on both hemolysis and the Tm of B3, but it stabilizes spectrin (delta Tm = 1.5 K) against thermal denaturation.(ABSTRACT TRUNCATED AT 400 WORDS)