The bi-pedal ape: Plasticity and asymmetry in footedness

Quantification in shooting precision for preferred and non-preferred foot in college soccer players using the 95% equal confidence ellipse

Shooting precision is a fundamental characteristic in soccer, yet the probabilistic structure and magnitude of precision in soccer shooting remain quantitatively unexplored. This study aimed to quantify shooting precision using measures derived from the bivariate normal distribution for both preferred and non-preferred feet. Sixteen right-footed collegiate soccer players participated by performing instep kicks aiming at targets which are placed close to the left and right top corners of the soccer goal. We used bivariate normal distribution modeled the ball positions, revealing an ellipsoidal distribution, and the area of the 95% confidence ellipses served as an index of precision. Repeated measures ANOVAs revealed a significant main effect of the kicking foot. For shots aimed at the same side as the kicking foot, the area of the 95% confidence ellipse was 6.17 ± 1.93 m2 (mean ± SD) for the preferred foot and 10.22 ± 3.53 m2 for the non-preferred foot. Similar results were observed for shots aimed at the opposite side of the kicking foot. These quantitative findings hold promise for advancing soccer research and enhancing practical applications in soccer skill assessment.

Profiling the different types of laterality in high-performance male and female Gaelic footballers

When performing sporting tasks, individuals may use a single side for all tasks (consistently unilateral), both sides equally on each task (consistent bilateral), different sides for different tasks (mixed laterality) or opposing sides when performing tasks with hands versus feet (crossed laterality). Previous research has largely focused on analysing laterality within a single skill. This study used notational analysis to investigate laterality profiles across four skills (two with the hands: hand pass and hop; and two with the feet: kick pass and solo) within high-performance Gaelic Football players. Fifty females and 83 males completed sufficient trials on all four skills to be included. While the majority of players were unilateral, some players displayed a different laterality profile. No player was consistently bilateral for all four skills. Chi-squared tests of independence revealed minimal differences between males and females in levels of partial bilaterality, crossed laterality or mixed laterality. Left-sided male and female players were significantly less lateralized than their right-sided counterparts for all assessed skills. Overall, findings show that laterality is complex, idiosyncratic and non-binary. Recognizing the idiosyncratic nature of limb dominance has numerous applications for coaches involved in player development, opposition analysis and sport scientists involved in talent development.

Profiling Bilateral Skills in High-Performance Male and Female Gaelic Footballers

Bilateral skill symmetry in sport refers to an individual's ability to successfully perform sporting actions with both sides of the body. Two scarcely researched areas in relation to bilateral skills are the effects of opposition proximity on skill execution and bilateral skill in high-performance female athletes. In this study, we used Nacsport to code all skill executions (hand pass, kick pass, hop, solo and shot) during 121 games by both male and female participants (76 male, 45 female), classified as Tier 1 (n = 181, 134) and Tier 2 (n = 238, 115) high performance, adult Gaelic Football players. Irrespective of the participants' tier group or gender, these players relied upon their dominant side for most skill executions (Kick Pass Dominant Foot Mdn: MT1 = 90%, MT2 = 98.6%, FT1 = 100%, FT2 = 100%; Solo Dominant Foot: Mdn MT1 = 95%, MT2 = 97.3%, FT1: 100%, FT2: 100%; Hand Pass Dominant Hand Mdn: MT1: 83.7%, MT2: 99%, FT1: 95.5%, FT2: 95.5%; Hop Dominant Hand Mdn: MT1: 91.9%, MT2: 94.7%, FT1: 98.1%, FT2: 98.1%; Play Dominant Foot Mdn: MT1: 74.5%, MT2: 94.5%, FT1: 94.7%, FT2: 88.2%). There were no consistent differences between tier groups or genders in relation to dominant side use, but top tier male players were generally less reliant on the dominant limb than were female players from both tiers. In general, top tier male players performed more successfully than either second tier male players or female players in both tiers. Most skills were executed under conditions of low opponent proximity, limiting the requirement for participants to use their non-dominant limbs. These findings illustrate the demands of Gaelic football in relation to bilateral skills, and we identified new research questions for future investigators.

The Relationship Among Acceleration, Deceleration and Changes of Direction in Repeated Small Sided Games

The change of direction (COD) ability is perhaps the most significant fitness component in team sport games. One of the best ways to develop COD as well as other components of the game in soccer is the regular inclusion of small sided games (SSGs) in the training process. Therefore, the aim of this research was to determine changes in physiological and kinematic variables in repeated SSGs in youth soccer players. Additionally, we investigated the relationship between selected IMA variables such as acceleration, deceleration and changes of direction. Participants included sixteen U17 soccer players from a 2^nd league professional team with a high aerobic capacity. The study design involved six 3-min 4 × 4 SSGs with goalkeepers and with a 3-min rest interval between games, during two training sessions played on a field of 25 x 35 m. The results showed that the intervention protocol consisting of repeated SSGs generated an intensity below the anaerobic threshold. This allowed for the maintenance of all variables (Heart Rate, Total Distance Covered, Velocity, Acceleration, Deceleration, Change of Direction) at a similar level throughout the subsequent six SSGs. The analysis revealed that in the six SSGs, players performed the most Acc and Dec, then COD Right and the least COD Left. From the third game on, a decrease in the number of COD Right was noticed. We hypothesized that progressive neuromuscular fatigue on the dominant side caused a more symmetrical trend in COD.

Maladaptive One-Leg Balance Control in Parkinson’s Disease

Balance disorders are very frequent in Parkinson’s disease (PD). One-leg stance performance is a predictor of fall risk. We investigated one-leg stance strategies in people with PD. We hypothesized that patients would choose, and better perform on, the leg on the least affected body side. Fifty participants with 2 to 19 years of PD duration stood on one leg while ON medication. The leg spontaneously chosen was recorded. Performance was compared between the spontaneously chosen vs. contralateral, and most vs. least stable legs. Influence of disease duration, severity, age, cognition, and motor fluctuations was analyzed. Twenty-eight patients spontaneously stood on the leg of the least affected body side, which was not always the most stable one. The chosen standing leg was influenced by disease duration with a switch between the least vs. most affected body side after seven years of disease duration. Fourteen patients (28%) spontaneously stood on their least stable leg. Thus, some patients with PD choose the least stable leg when asked to perform one-leg stance. It is important to identify these patients since they may be at greater risk of falls and/or gait difficulties. Specific rehabilitation may help prevent such maladaptive strategy.

Participation of Soccer Training Improves Lower Limb Coordination and Decreases Motor Lateralization

Athletes, who display less lateralization, are considered to be more successful in their sports. Therefore, it is important to test the lateralization profiles of the athletes to determine future prospects. Soccer is one of the sports where lateralization plays an important role because performing the passes and kicks with either foot may increase the success rate. Improved lower limb coordination is also very essential to perform the soccer skills more efficiently. Thus, the purpose of this study was to investigate the motor lateralization profiles of youth soccer players and to compare the same lateralization to non-athletes. A total of 28 healthy youth (14 soccer players) aged between 14 and 16 years voluntarily participated in this study. All participants were right-footed and were asked to hit the targets with their either foot maintaining accuracy in a custom-made virtual reality interface. Final position error (FPE) and foot path deviation from linearity (FPDL) were calculated to test motor lateralization for each foot and group. Two-way Mixed Model ANOVA was conducted for each dependent variable. Results indicated significant differences for FPDL between groups, while there were no significant differences between groups and within feet for FPE. Nonathletes had significantly higher FPDL with their nondominant foot compared to their dominant foot, which was not observed among soccer players. Overall, nonathletes' movements were more curvature path compared to soccer players, thus, can be considered as less coordinated. As soccer players did not show a difference between their feet on FPDL and performed better than nonathletes, soccer participation can improve lower limb coordination as well as alter motor performance and lateralization.

The Development of Bilateral Skill Symmetry: Insights From Gaelic Football Players and Coaches

Developing players who are adept at using both sides of the body (i.e., bilateral skill) is a challenge for coaches in many sports. With players being required to execute a range of skills with hand and foot on both sides of the body, Gaelic football provides an ideal natural laboratory for the study of laterality. Previous quantitative research has produced equivocal findings regarding the importance of bilateral skill performance in sport. In light of this equivocality, this paper utilized a qualitative approach to distill the beliefs and experiences of 14 players and five coaches who had performed at the highest level in Gaelic football. Three higher order categories were produced from the transcripts: the importance of being bilaterally skilled, the potential to develop bilateral skill, and methods to develop bilateral skills. Overall, this study highlights lessons for the design of future quantitative studies of bilateral skill in sport and should stimulate reflection on current practice regarding both short- and long-term bilateral skill development on the part of researchers, applied sport scientists, and coaches.

How Positional Constraints Affect Footedness in Football: A Notational Analysis of Five Leagues in Europe

In elite-level soccer, the ability to take shots with both limbs from different positions in the pitch may be key to success. This research aimed to: 1) analyze footedness of elite-football players in European leagues during shooting by computing frequency of right- and left-foot use and accuracy; and 2) investigate whether an athlete's distance from the target (goal, penalty, and outside penalty area) and pitch zone (center, left, or right from the goal) can constrain foot selection during shooting. We analyzed 1826 games from the 2017/18 season, divided between: Spanish LaLiga (380 matches); Italian Serie A (380 matches); English Premier League (380 matches); German Bundesliga (306 matches); and French Ligue 1 (380 matches). Results revealed asymmetrical proportions of foot selection, favoring the preferred foot for right- and left-footed athletes. Frequency of preferred foot selection increased as a function of distance from the target (i.e., the farther the athlete, higher the percentage of preferred foot selection). Shots taken from the left side were more often performed with the right foot and vice-versa, for both left- and right-footed athletes. Interestingly, asymmetries were observed only in foot selection, but not in performance, as success rate did not vary between limbs in any position.

The dominant leg is more likely to get injured in soccer players: systematic review and meta-analysis

In soccer (football), dominant limb kicking produces higher ball velocity and is used with greater frequency than the non-dominant limb. It is unclear whether limb dominance has an effect on injury incidence. The purpose of this systematic review with meta-analysis is to examine the relationship between limb dominance and soccer injuries. Studies were identified from four online databases according to PRISMA guidelines to identify studies of soccer players that reported lower extremity injuries by limb dominance. Relevant studies were assessed for inclusion and retained. Data from retained studies underwent meta-analyses to determine relative risk of dominant versus non-dominant limb injuries using random-effects models. Seventy-four studies were included, with 36 of them eligible for meta-analysis. For prospective lower extremity injury studies, soccer players demonstrated a 1.6 times greater risk of injury to the dominant limb (95% CI [1.3-1.8]). Grouped by injury location, hamstring (RR 1.3 [95% CI 1.1-1.4]) and hip/groin (RR 1.9 [95% CI 1.3-2.7]) injuries were more likely to occur to the dominant limb. Greater risk of injury was present in the dominant limb across playing levels (amateurs RR 2.6 [95% CI 2.1-3.2]; youths RR 1.5 [95% CI 1.26-1.67]; professionals RR 1.3 [95% CI 1.14-1.46]). Both males (RR 1.5 [95% CI 1.33-1.68)] and females (RR 1.5 [95% CI 1.14-1.89]) were more likely to sustain injuries to the dominant limb. Future studies investigating soccer injury should adjust for this confounding factor by using consistent methods for assigning limb dominance and tracking use of the dominant versus non-dominant limb.

Physical Activity of the Right- and Left-Footed Professional Soccer Players from Symmetrical Defensive Positions

The main purpose of this study was to compare the physical match performance of right- and left-footed external defenders during official matches of Polish Ekstraklasa. The sample comprised 991 individual observations from 296 matches during the 2019/2020 season. Variables such as total distance, distance covered in high-speed running and sprinting, and number of high-intensity runs were analysed. Additionally, the data were presented in relation to match duration and effective playing time. Right external defenders (right ED) covered significantly longer total distance (p < 0.001, 1.5%), high-speed running distance (p < 0.001, 5.6%) and sprinting distance (p < 0.001, 11.4%) compared to left external defenders (left ED). The number of high-intensity runs was greater for right RD as well (p < 0.001, 6.4%). Physical match activity for left ED who are left-footed was significantly higher (p < 0.001) in comparison with right-footed left ED. The number of offensive actions played on the right side of the pitch was significantly (p < 0.001) higher than those performed on the left side. Players whose dominant foot is in accordance with the side of the pitch cover longer distances during the match. Moreover, the number of offensive actions played through the wings could affect the physical performance of external defenders.

A Narrative Review of Limb Dominance: Task Specificity and the Importance of Fitness Testing

ABSTRACT

Virgile, A and Bishop, C. A narrative review of limb dominance: Task specificity and the importance of fitness testing. J Strength Cond Res 35(3): 846-858, 2021-Preferential limb function must be sustained through repetitious asymmetrical activities for continuous athletic development and, ultimately, optimal athletic performance. As such, the prevalence of limb dominance and between-limb differences is common in athletes. Severe between-limb differences have been associated with reductions in athletic performance and increased injury risk in athletes. However, in the current literature, the terms limb preference and limb dominance have been used interchangeably. Together, these terms include a limb that is subjectively preferred and one that is objectively dominant in 1 or more performance measures from a variety of athletic tasks. In this review, we (a) discuss reported correspondence between task-specific limb preference and limb dominance outcomes in athletes, (b) provide greater context and distinction between the terms limb preference and limb dominance, and (c) offer pragmatic strategies for practitioners to assess context-specific limb dominance. A limb that is subjectively preferred is not necessarily objectively dominant in 1 or more athletic qualities or sport-specific tasks. Further to this, a limb that is objectively superior in 1 task may not exhibit such superiority in a separate task. Thus, limb preference and limb dominance are both task-specific. As such, we propose that practitioners intentionally select tasks for limb dominance assessment which resemble the most relevant demands of sport. Because limb dominance profiles are inconsistent, we suggest that practitioners increase assessment frequency by integrating limb dominance testing into standard training activities. This will allow practitioners to better understand when changes reflect sport-specific adaptation vs. potential performance or injury ramifications.

Four meta-analyses across 164 studies on atypical footedness prevalence and its relation to handedness

Human lateral preferences, such as handedness and footedness, have interested researchers for decades due to their pronounced asymmetries at the population level. While there are good estimates on the prevalence of handedness in the population, there is no large-scale estimation on the prevalence of footedness. Furthermore, the relationship between footedness and handedness still remains elusive. Here, we conducted meta-analyses with four different classification systems for footedness on 145,135 individuals across 164 studies including new data from the ALSPAC cohort. The study aimed to determine a reliable point estimate of footedness, to study the association between footedness and handedness, and to investigate moderating factors influencing footedness. We showed that the prevalence of atypical footedness ranges between 12.10% using the most conservative criterion of left-footedness to 23.7% including all left- and mixed-footers as a single non-right category. As many as 60.1% of left-handers were left-footed whereas only 3.2% of right-handers were left-footed. Males were 4.1% more often non-right-footed compared to females. Individuals with psychiatric and neurodevelopmental disorders exhibited a higher prevalence of non-right-footedness. Furthermore, the presence of mixed-footedness was higher in children compared to adults and left-footedness was increased in athletes compared to the general population. Finally, we showed that footedness is only marginally influenced by cultural and social factors, which play a crucial role in the determination of handedness. Overall, this study provides new and useful reference data for laterality research. Furthermore, the data suggest that footedness is a valuable phenotype for the study of lateral motor biases, its underlying genetics and neurodevelopment.

Influence of playing position and laterality in centripetal force and changes of direction in elite soccer players

The purpose of the present study was to: (a) assess centripetal force (CentF) and changes of direction (COD) in elite soccer players according to playing position (central defender, CD; lateral defender, LD; central midfielder, CM; lateral midfielder, LM; forward, FW), laterality (right-footed vs. left-footed) and field zone (central vs. lateral), and (b) analyze the relationship between anthropometric characteristics (age, weight, height, body mass and fat mass) and non-linear locomotion workload. Thirty professional soccer players (age: 26.57±5.56 years) were tracked during the 2017–2018 season during friendly, national and international matches (38 total games) using inertial measurement devices. CentF and COD were the variables extracted for analysis. A one-way ANOVA was used for playing position comparison, a t-test for laterality and field zone, and Pearson’s correlation coefficient to analyze relationships between anthropometric characteristics and dependent variables. There were differences by playing position in COD (556.33-to-412.18), R₂₀COD (484.36-to-354.81) and R₆₀COD (48.38-to-38.61) (p < .01; ω_p² = 0.03-to-0.05; CD>CM>LD>LM = FW); in COD_HIA (49.75-to-37.11), R₂₀COD_HIA (16.04-to-9.11) and R₆₀COD_HIA (10.64-to-9.11) (p < .01; ω_p² = 0.03-to-0.07; CM>FW>LM>CD = LD); in COD_SPRINT (14.56-to-8.40) and R₂₀COD_SPRINT (3.29-to-1.40) (p < .01; ω_p² = 0.03-to-0.04; FW = LM = CM>CD = LD); and in CentF_MAX both in clockwise (992.04-to-902.09N) and counterclockwise (999.24-to-872.61N) directions (p < .02; ω_p² = 0.02-to-0.07; FW = CD>CM = LM = LD). The highest values of counterclockwise CentF were performed by left-footed players in the central zone (p < .001; d = 0.71-to-1.44) and clockwise CentF by right-footed players (p < .001; d = 0.04-to-0.55) in the lateral field zone. Moderate correlations were found between age, body mass and high intensity/sprints COD and repeated COD ability (p < .05; r = 0.235-to-0.383). Therefore, team staff should consider anthropometric characteristics, playing position, laterality and field zone to individualize training workload related to non-linear locomotion in soccer.

Lateral kinetic proficiency and asymmetry in backstroke start performed with horizontal and vertical handgrips

We aimed to compare preferred, non-preferred, hand, foot kinetics and their asymmetry in two backstroke start variants. Complementarily, asymmetries were correlated to the resultant take-off velocity. Nine swimmers completed four 15 m backstroke starts with horizontal handgrips and four with vertical handgrips on an instrumented block (right, left hand, foot forces and impulse, normalised to swimmers' weight and time). We applied handedness and footedness questionnaires. Preferred hand and foot depicted a very and most likely moderate to large increase on horizontal force before hands-off (-0.51 ± 0.10; -0.47 ± 0.10; 0.87 ± 0.15; 0.90 ± 0.18 (N/N)) and a very and most likely large to very large increase on horizontal impulse (-0.28 ± 0.05; -0.26 ± 0.04; 0.50 ± 0.03; 0.51 ± 0.04 (N/N)*(s/s)) in both variants. Non-preferred hand and foot showed a very likely large to moderate increase (95% to 99%) on vertical and lateral impulse (0.30 ± 0.03; 0.31 ± 0.03; 0.07 ± 0.04; 0.05 ± 0.03 (N/N)*(s/s)) in both variants. The horizontal handgrip demonstrated likely moderate greater horizontal forces asymmetry on hands in the starting signal (-20.39 ± 7.16 (N/N), 92%), before hands-off (-71.46 ± 24.48 (N/N), 90%) and impulse asymmetry (-21.13 ± 5.80 (N/N), 94%). Asymmetry and resultant take-off velocity in both variants were strongly associated (r = -0.733 and -0.833 for feet horizontal impulse). Kinetics lateralisation was noticed in backstroke start and asymmetry hampers desirable performance.

Footedness Is Associated with Self-reported Sporting Performance and Motor Abilities in the General Population

Left-handers may have strategic advantages over right-handers in interactive sports and innate superior abilities that are beneficial for sports. Previous studies relied on differing criteria for handedness classification and mostly did not investigate mixed preferences and footedness. Footedness appears to be less influenced by external and societal factors than handedness. Utilizing latent class analysis and structural equation modeling, we investigated in a series of studies (total N > 15300) associations of handedness and footedness with self-reported sporting performance and motor abilities in the general population. Using a discovery and a replication sample (ns = 7658 and 5062), Study 1 revealed replicable beneficial effects of mixed-footedness and left-footedness in team sports, martial arts and fencing, dancing, skiing, and swimming. Study 2 (n = 2592) showed that footedness for unskilled bipedal movement tasks, but not for skilled unipedal tasks, was beneficial for sporting performance. Mixed- and left-footedness had effects on motor abilities that were consistent with published results on better brain interhemispheric communication, but also akin to testosterone-induced effects regarding flexibility, strength, and endurance. Laterality effects were only small. Possible neural and hormonal bases of observed effects need to be examined in future studies.

Asymmetrical motor behaviour as a window to early leg preference: a longitudinal study in infants 7-12 months of age

This longitudinal study explored leg preference in infancy during half-kneel pulling-to-stand (PTS) and asymmetrical four-point kneeling, which is part of the typical motor repertoire of infants. The special characteristics of the half-kneel PTS as a discrete task, performed in a bilateral context provide the opportunity to explore leg preference during an asymmetrical behaviour. Twenty-seven infants were observed in their homes, every 3 weeks between the ages of 7-12 months. Leg preference was determined by the "lead-out" limb used as the infants pulled to stand from the half-kneeling position (half-kneel PTS). As a complementary measure, the leading leg during asymmetrical four-point kneeling and crawling ("asymmetrical four-point patterns") was used in the 10 infants who developed these patterns. The infants studied showed a general preference for using a leading leg during half-kneel PTS, which was mostly consistent over the study period. A strong correlation was found between leg preferences during half-kneel PTS and asymmetrical four-point patterns. The findings documented functional asymmetry in infant lower limbs during half-kneel PTS and asymmetrical four-point patterns, highlighting the importance of the tasks used to define leg preference.

Distribution of plantar pressures during gait in different zones of the foot in healthy children: the effects of laterality

The objective was to determine whether gait is symmetric in healthy children 6-7 years of age and to assess the effects of laterality and the anatomical zone of the foot. 46 children were subjected to gait symmetry analysis in which the plantar and lateral pressures associated with kicking a ball, static balance, and dynamic support were measured. There were no significant differences in the average pressure exerted by the right and left feet based on the laterality of the child. Independent of each laterality test, a greater pressure on the right rearfoot was observed compared to the left rearfoot and on the left midfoot and forefoot compared to the right.

Quantifying cerebral asymmetries for language in dextrals and adextrals with random-effects meta analysis

Speech and language-related functions tend to depend on the left hemisphere more than the right in most right-handed (dextral) participants. This relationship is less clear in non-right handed (adextral) people, resulting in surprisingly polarized opinion on whether or not they are as lateralized as right handers. The present analysis investigates this issue by largely ignoring methodological differences between the different neuroscientific approaches to language lateralization, as well as discrepancies in how dextral and adextral participants were recruited or defined. Here we evaluate the tendency for dextrals to be more left hemisphere dominant than adextrals, using random effects meta analyses. In spite of several limitations, including sample size (in the adextrals in particular), missing details on proportions of groups who show directional effects in many experiments, and so on, the different paradigms all point to proportionally increased left hemispheric dominance in the dextrals. These results are analyzed in light of the theoretical importance of these subtle differences for understanding the cognitive neuroscience of language, as well as the unusual asymmetry in most adextrals.

One hand or the other? Effector selection biases in right and left handers

Much debate in the handedness literature has centred on the relative merits of questionnaire-based measures assessing hand preference versus simple movement tasks such as peg moving or finger tapping, assessing hand performance. A third paradigm has grown in popularity, which assesses choices by participants when either hand could be used to execute movements. These newer measures may be useful in predicting possible "reversed" asymmetries in proportions of non-right handed ("adextral") people. In the current studies we examine hand choice in large samples of dextral (right handed) and adextral participants. Unlike in some previous experiments on choice, we found that left handers were as biased towards their dominant hand as were right handers, for grasping during a puzzle-making task (study 1). In a second study, participants had to point to either of two suddenly appearing targets with one hand or the other. In study 2, left handers were not significantly less one handed than their right-handed counterparts as in study 1. In a final study, we used random effects meta analysis to summarise the possible differences in hand choice between left handers and right handers across all hand choice studies published to date. The meta analysis suggests that right handers use their dominant hand 12.5% more than left handers favour their dominant hand (with 95% confidence that the real difference lies between 7% and 18%). These last results suggest that our two experiments reported here may represent statistical Type 2 errors. This mean difference may be related to greater left hemispheric language and praxic laterality in right handers. Nevertheless, more data are needed regarding the precise proportions of left and right handers who favour their preferred hands for different tasks.

Evidence for general right-, mixed-, and left-sidedness in self-reported handedness, footedness, eyedness, and earedness, and a primacy of footedness in a large-sample latent variable analysis

Lateral preferences are important for the study of cerebral lateralization and may be indicative of neurobehavioral disorders, neurodevelopmental instability, and deficits in lateralization. Previous studies showed that self-reported preferences are also concordantly interrelated, suggesting a common genetic or biological origin, sidedness. However, with regard to the assessment and classification of lateral preferences, there is a dearth of psychometric studies, but a need for psychometrically validated instruments that can be reliably used in applied research. Based on three independent large samples (total N>15,100), this study investigated the psychometric properties of widely-used lateral preference scales of handedness, footedness, eyedness, and earedness. Preferences were consistently and replicably categorical, consisting of right, mixed, and left preferences each, underlining that primarily qualitative, rather than quantitative, differences differentiate lateral preferences. Right-, mixed-, and left-sidedness underlay the individual preferences, but sidedness alone could not fully explain the observed inter-relations. Footedness was the single most important indicator of sidedness. Our data were further consistent with predictions of right shift theory and corroborated a 'pull-to-concordance' in hand-foot preferences. We recommend the use of psychometrically validated scales and of a trichotomous classification of lateral preferences in future research, but conclude that handedness may be a biased indicator of underlying sidedness. Footedness needs to be examined more closely with regard to cerebral lateralization, neurodevelopmental disorders, and neurodevelopmental instability.

Foot use and hand preference during feeding in captive black-and-white snub-nosed monkeys (Rhinopithecus bieti)

Postural origin theory predicts that body postures are related to hand preference in nonhuman primates due to hemispheric specialization. Foot preference, especially in manipulating objects, is also a good predictor of hemispheric specialization in humans. We studied limb (hand and foot) preferences in 11 captive adult black-and-white snub-nosed monkeys (Rhinopithecus bieti) to see how limb preference is influenced by postures and foot manipulation. Hand preference was significantly different for this group between quadrupedal standing and clinging postures, and sitting and clinging postures, but not between bipedal standing and clinging postures. Individuals were significantly more likely to use the right hand in the clinging posture than in quadrupedal standing or sitting postures. In the sitting posture, individuals maintained their respective hand preference even when the food was on the other side of the body. There was a gender difference in the sitting posture, where females preferred their right hand but males preferred their left. Individuals who did not routinely use their feet to manipulate objects, compared to those who did, shifted to greater right hand use from the clinging posture to the bipedal posture. One male individual and his offspring were more likely to use their feet to manipulate objects than the rest of the monkeys. In the present study, we reveal the first evidence of a postural effect on hand preference in R. bieti as well as a foot preference in this species. Our results mostly agree with the postural origin theory and hemispheric specialization.

Looking at eye dominance from a different angle: is sighting strength related to hand preference?

Sighting dominance (the behavioural preference for one eye over the other under monocular viewing conditions) has traditionally been thought of as a robust individual trait. However, Khan and Crawford (2001) have shown that, under certain viewing conditions, eye preference reverses as a function of horizontal gaze angle. Remarkably, the reversal of sighting from one eye to the other depends on which hand is used to reach out and grasp the target. Their procedure provides an ideal way to measure the strength of monocular preference for sighting, which may be related to other indicators of hemispheric specialisation for speech, language and motor function. Therefore, we hypothesised that individuals with consistent side preferences (e.g., right hand, right eye) should have more robust sighting dominance than those with crossed lateral preferences. To test this idea, we compared strength of eye dominance in individuals who are consistently right or left sided for hand and foot preference with those who are not. We also modified their procedure in order to minimise a potential image size confound, suggested by Banks et al. (2004) as an explanation of Khan and Crawford's results. We found that the sighting dominance switch occurred at similar eccentricities when we controlled for effects of hand occlusion and target size differences. We also found that sighting dominance thresholds change predictably with the hand used. However, we found no evidence for relationships between strength of hand preference as assessed by questionnaire or by pegboard performance and strength of sighting dominance. Similarly, participants with consistent hand and foot preferences did not show stronger eye preference as assessed using the Khan and Crawford procedure. These data are discussed in terms of indirect relationships between sighting dominance, hand preference and cerebral specialisation for language and motor control.

Plasticity of human handedness: decreased one-hand bias and inter-manual performance asymmetry in expert basketball players

Athletes frequently have to adapt their skills to fast changes of play, often requiring the flexible execution of a particular movement skill with either hand. To assess the influence of sport-specific expertise and extensive sport training on human laterality, a video analysis of regular basketball games was performed for professional, semi-professional, and amateur players to investigate how non-dominant hand use and proficiency change with increasing expertise. Our results showed that the right-hand (i.e. dominant hand) bias in basketball players is reduced with increasing expertise (i.e., competitive level). Accordingly, we found that professional players use their non-dominant hand more often and with greater success than semi-professional and amateur players. This was true for most of the basketball-specific skills. Based on these results, we assume that increasing amounts of bilateral practice can lead to a shift in task-specific manual preference towards a higher use of both hands in competition, as well as to a higher proficiency for non-dominant hand actions in particular. From an applied perspective, the more frequent use and higher proficiency of the non-dominant hand in professional basketball players, compared with amateurs, suggests that the context-specific and skilled use of the non-dominant hand is crucial for successful play at higher competitive levels in the sport of basketball.