Sports Medicine

The importance of trunk muscle strength (TMS) for physical fitness and athletic performance has been demonstrated by studies reporting significant correlations between those capacities. However, evidence-based knowledge regarding the magnitude of correlations between TMS and proxies of physical fitness and athletic performance as well as potential effects of core strength training (CST) on TMS, physical fitness and athletic performance variables is currently lacking for trained individuals. The aims of this systematic review and meta-analysis were to quantify associations between variables of TMS, physical fitness and athletic performance and effects of CST on these measures in healthy trained individuals. PubMed, Web of Science, and SPORTDiscus were systematically screened from January 1984 to March 2015. Studies were included that investigated healthy trained individuals aged 16–44 years and tested at least one measure of TMS, muscle strength, muscle power, balance, and/or athletic performance. Z-transformed Pearson’s correlation coefficients between measures of TMS and physical performance were aggregated and back-transformed to r values. Further, to quantify the effects of CST, weighted standardized mean differences (SMDs) of TMS and physical performance were calculated using random effects models. The methodological quality of CST studies was assessed by the Physiotherapy Evidence Database (PEDro) scale. Small-sized relationships of TMS with physical performance measures (−0.05 ≤ r ≤ 0.18) were found in 15 correlation studies. Sixteen intervention studies revealed large effects of CST on measures of TMS (SMD = 1.07) but small-to-medium-sized effects on proxies of physical performance (0 ≤ SMD ≤ 0.71) compared with no training or regular training only. The methodological quality of CST studies was low (median PEDro score = 4). Our findings indicate that TMS plays only a minor role for physical fitness and athletic performance in trained individuals. In fact, CST appears to be an effective means to increase TMS and was associated with only limited gains in physical fitness and athletic performance measures when compared with no or only regular training.

It is becoming increasingly clear that adaptations, initiated by exercise, can be amplified or reduced by nutrition. Various methods have been discussed to optimize training adaptations and some of these methods have been subject to extensive study. To date, most methods have focused on skeletal muscle, but it is important to note that training effects also include adaptations in other tissues (e.g., brain, vasculature), improvements in the absorptive capacity of the intestine, increases in tolerance to dehydration, and other effects that have received less attention in the literature. The purpose of this review is to define the concept of periodized nutrition (also referred to as nutritional training) and summarize the wide variety of methods available to athletes. The reader is referred to several other recent review articles that have discussed aspects of periodized nutrition in much more detail with primarily a focus on adaptations in the muscle. The purpose of this review is not to discuss the literature in great detail but to clearly define the concept and to give a complete overview of the methods available, with an emphasis on adaptations that are not in the muscle. Whilst there is good evidence for some methods, other proposed methods are mere theories that remain to be tested. ‘Periodized nutrition’ refers to the strategic combined use of exercise training and nutrition, or nutrition only, with the overall aim to obtain adaptations that support exercise performance. The term nutritional training is sometimes used to describe the same methods and these terms can be used interchangeably. In this review, an overview is given of some of the most common methods of periodized nutrition including ‘training low’ and ‘training high’, and training with low- and high-carbohydrate availability, respectively. ‘Training low’ in particular has received considerable attention and several variations of ‘train low’ have been proposed. ‘Training-low’ studies have generally shown beneficial effects in terms of signaling and transcription, but to date, few studies have been able to show any effects on performance. In addition to ‘train low’ and ‘train high’, methods have been developed to ‘train the gut’, train hypohydrated (to reduce the negative effects of dehydration), and train with various supplements that may increase the training adaptations longer term. Which of these methods should be used depends on the specific goals of the individual and there is no method (or diet) that will address all needs of an individual in all situations. Therefore, appropriate practical application lies in the optimal combination of different nutritional training methods. Some of these methods have already found their way into training practices of athletes, even though evidence for their efficacy is sometimes scarce at best. Many pragmatic questions remain unanswered and another goal of this review is to identify some of the remaining questions that may have great practical relevance and should be the focus of future research.

Concentrations of endogenous sex hormones fluctuate across the menstrual cycle (MC), which could have implications for exercise performance in women. At present, data are conflicting, with no consensus on whether exercise performance is affected by MC phase. To determine the effects of the MC on exercise performance and provide evidence-based, practical, performance recommendations to eumenorrheic women. This review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Four databases were searched for published experimental studies that investigated the effects of the MC on exercise performance, which included at least one outcome measure taken in two or more defined MC phases. All data were meta-analysed using multilevel models grounded in Bayesian principles. The initial meta-analysis pooled pairwise effect sizes comparing exercise performance during the early follicular phase with all other phases (late follicular, ovulation, early luteal, mid-luteal and late luteal) amalgamated. A more comprehensive analysis was then conducted, comparing exercise performance between all phases with direct and indirect pairwise effect sizes through a network meta-analysis. Results from the network meta-analysis were summarised by calculating the Surface Under the Cumulative Ranking curve (SUCRA). Study quality was assessed using a modified Downs and Black checklist and a strategy based on the recommendations of the Grading of Recommendations Assessment Development and Evaluation (GRADE) working group. Of the 78 included studies, data from 51 studies were eligible for inclusion in the initial pairwise meta-analysis. The three-level hierarchical model indicated a trivial effect for both endurance- and strength-based outcomes, with reduced exercise performance observed in the early follicular phase of the MC, based on the median pooled effect size (ES0.5 = − 0.06 [95% credible interval (CrI): − 0.16 to 0.04]). Seventy-three studies had enough data to be included in the network meta-analysis. The largest effect was identified between the early follicular and the late follicular phases of the MC (ES0.5 = − 0.14 [95% CrI: − 0.26 to − 0.03]). The lowest SUCRA value, which represents the likelihood that exercise performance is poor, or among the poorest, relative to other MC phases, was obtained for the early follicular phase (30%), with values for all other phases ranging between 53 and 55%. The quality of evidence for this review was classified as “low” (42%). The results from this systematic review and meta-analysis indicate that exercise performance might be trivially reduced during the early follicular phase of the MC, compared to all other phases. Due to the trivial effect size, the large between-study variation and the number of poor-quality studies included in this review, general guidelines on exercise performance across the MC cannot be formed; rather, it is recommended that a personalised approach should be taken based on each individual's response to exercise performance across the MC.

Postoperative rehabilitation is a major factor in the success of an anterior cruciate ligament (ACL) reconstruction procedure. Clinical investigations of patients after ACL reconstruction have shown that immobilisation of the knee, or restricted motion without muscle contraction, leads to undesired outcomes for the articular, ligamentous, and musculature structures that surround the knee. Early joint motion is beneficial for; reducing pain, capsular contractions, articular cartilage, and for minimising scar formation that limit joint motion. These findings, combined with graft materials that have biomechanical properties similar to the normal ACL, and adequate fixation strength, have led many to recommend aggressive rehabilitation programmes that involve contraction of the dominant quadriceps muscles. Recently, a prospective, randomised study of rehabilitation following ACL reconstruction has presented evidence that a closed kinetic chain exercise programme (foot fixed against a resistance) results in anterior-posterior knee laxity values that are similar to the contralateral normal knee. Also, open kinetic chain exercises (foot not fixed against a resistance) result in increased anterior-posterior knee laxity compared with the normal knee. Criteria must be observed because the relationship between rehabilitation exercises and the healing response of an ACL graft is unknown at present. Biomechanical studies of healing ACL grafts performed in animals have shown that the graft requires a long time to revascularise and heal, and that the biomechanical behaviour of the graft never returns to normal. Functional knee braces provide a protective strain-shielding effect on the ACL when anterior shear loads and internal torques are applied to the knee in the non-weight-bearing condition. However, the strain shielding effect of functional braces decrease as the magnitude of anterior shear and internal torque applied to the knee increase. Future studies should strive to determine the actual loads transmitted across the knee and ACL graft strain during various rehabilitation exercises and relate these to the healing response of the knee and graft.

The use of hyaluronans for the treatment of pain in patients with osteoarthritis of the knee is well established. There are growing data to suggest that they may also alter the rate of disease progression. Reviewed here are preliminary data that also indicate a potential use for hyaluronans in the treatment of inflammatory arthropathies (e.g. acute joint trauma and fractures) that require long periods of immobilisation, and in tissue engineering for chondral defects. Although the trials that have investigated the use of hyaluronan therapy for the management of traumatic and degenerative musculoskeletal disorders seen in sports medicine have limitations in design and patient number, the results have been promising and suggest that larger controlled clinical trials are warranted.