Effects of a Tailored Exercise Intervention in Acutely Hospitalized Oldest Old Diabetic Adults: An Ancillary Analysis

OBJECTIVE

To analyze the effects of a tailored exercise intervention in acutely hospitalized elderly diabetic patients.

RESEARCH DESIGN AND METHODS

This is an ancillary analysis of a randomized controlled trial (RCT). A total of 103 acutely hospitalized elderly adults (mean age ~87 years) with type II diabetes were randomized to an intervention (exercise, n = 54) or control group (usual care, n = 49). The primary endpoint was change in functional status from baseline to hospital discharge as assessed with the Barthel Index and the Short Physical Performance Battery (SPPB). Secondary endpoints comprised cognitive function and mood status, quality of life (QoL), incidence of delirium, and handgrip strength. Exercise-related side effects, length of hospital stay, and incidence of falls during hospitalization were also assessed, as well as transfer to nursing homes, hospital readmission, and mortality during a 3-month follow-up.

RESULTS

The median length of stay was 8 days (interquartile range, 4) for both groups. The intervention was safe and provided significant benefits over usual care on SPPB (2.7 [95% confidence interval (CI) 1.8, 3.5]) and Barthel Index (8.5 [95% CI: 3.9, 13.1]), as well as on other secondary endpoints such as cognitive status, depression, QoL, and handgrip strength (all P < 0.05). No significant between-group differences were found for the remainder of secondary endpoints.

CONCLUSIONS

An in-hospital individualized multicomponent exercise intervention was safe and effective for the prevention of functional and cognitive decline in acutely hospitalized elderly diabetic patients, although it had no influence on other endpoints assessed during hospitalization or at the 3-month follow-up after discharge.

Exercise Benefits Meet Cancer Immunosurveillance: Implications for Immunotherapy

Regular exercise reduces the risk of cancer. One potential mechanism for this efficacy is improved antitumor immunity. This is an important issue because evading immune destruction is a hallmark of cancer and immunotherapy is reshaping cancer treatment. Here we review recent developments reported by Wennerberg et al., Garritson et al., Martín-Ruiz et al., and Rundqvist et al. on the effects of exercise on anticancer immune cell effectors.

Exercise training effects on natural killer cells: a preliminary proteomics and systems biology approach

BACKGROUND

Regular exercise, particularly moderate-intensity continuous training (MICT), can improve immune function. Natural killer (NK) cells, a subset of lymphocytes that react to infections, are the most responsive innate immune cells to exercise, but the mechanisms underlying this are poorly understood. A type of exercise training that is gaining popularity in recent years is high-intensity interval training (HIIT), but how it affects NK cells is largely unknown. In fact, intense exercise has been traditionally viewed as a potential stressor to immune homeostasis. The purpose of this study was to determine in healthy, previously untrained adults (N=8 [3 male; 40±6 years]) the effects of an intervention consisting of 4-week MICT followed by 4-week HIIT on NK cells as compared with a pre-training (baseline) state.

METHODS

Participants were studied at three time points: baseline, mid-intervention (after MICT), and post-intervention (after HIIT). Main assessments included cytotoxicity assays, flow-cytometry analysis of NK cell surface markers, and interrogation of the cellular proteome using a systems biology approach.

RESULTS

A significant time effect was found for NK cell cytotoxicity (p<0.001), which was increased ~10-fold at both midand post-intervention versus baseline. No significant intervention effect was found for NK surface receptor expression, except for CXCR3 determined as mean fluorescence intensity (p=0.044, although with no significant differences in post hoc pairwise comparisons). The proteins showing a higher differential expression (Log2 fold-change > 10 and false discovery rate [FDR] q-value < 0.001) were COP9 signalosome subunit 3 (COPS3), DnaJ heat shock protein family member B11 (DNAJB11), histidyl-TRNA synthetase 1 (HARS), NIMA related kinase 9 (NEK9), nucleoporin 88 (NUP88), phosphoinositide-3-kinase regulatory subunit 1 (PIK3R1), regulator of chromosome condensation 2 (RCC2), TAO kinase 3 (TAOK3), transducin beta like 2 (TBL2), and ring finger protein 40 (RNF40). All were upregulated at mid-intervention compared with baseline, with the exception of HARS, which was downregulated. Four enriched pathways (FDR p<25%) were found: two related to transmembrane transport and cellular composition (downregulated at mid-intervention vs baseline), and two related to oxidation- reduction reactions (regulated at post-intervention versus baseline).

CONCLUSION

A progressive exercise intervention of MICT followed by HIIT induces a remarkable improvement in NK function compared with the untrained state, although at the mechanistic level the pathways involved seem to differ over time during the intervention.

Effects of Beef Protein Supplementation in Male Elite Triathletes: A Randomized, Controlled, Double-Blind, Cross-Over Study

OBJECTIVE

Beef protein extracts are growing in popularity in recent years due to their purported anabolic effects as well as to their potential benefits on hematological variables. The present randomized, controlled, double-blind, cross-over study aimed to analyze the effects of beef protein supplementation on a group of male elite triathletes (Spanish National Team).

METHODS

Six elite triathletes (age, 21 ± 3 years; VO2max, 71.5 ± 3.0 ml·kg·min-1) were randomly assigned to consume daily either 25 g of a beef supplement (BEEF) or an isoenergetic carbohydrates (CHO) supplement for 8 weeks, with both conditions being separated by a 5-week washout period. Outcomes, including blood analyses and anthropometrical measurements, were assessed before and after each 8-week intervention.

RESULTS

No effects of supplement condition were observed on body mass nor on skinfold thicknesses, but BEEF induced significant and large benefits over CHO in the thigh cross-sectional area (3.02%, 95%CI = 1.33 to 4.71%; p = 0.028, d = 1.22). Contrary to CHO, BEEF presented a significant increase in vastus lateralis muscle thickness (p = 0.046), but differences between conditions were not significant (p = 0.173, d = 0.87). Although a significantly more favorable testosterone-to-cortisol ratio (TCR) was observed for BEEF over CHO (37%, 95% CI = 5 to 68%; p = 0.028, d = 1.29), no significant differences were found for the hematological variables (i.e., iron, ferritin, red blood cell count, hemoglobin or hematocrit).

CONCLUSION

Beef protein supplementation seems to facilitate a more favorable anabolic environment (i.e., increased TCR and muscle mass) in male elite triathletes, with no impact on hematological variables.

Physical exercise and epicardial adipose tissue: A systematic review and meta-analysis of randomized controlled trials

We performed a meta-analysis of the effects of exercise on epicardial adipose tissue (EAT). A systematic search was conducted in PubMed and Scopus (since inception to 1 February 2020) of randomized controlled trials assessing the effects of exercise interventions alone (with no concomitant weight loss intervention) on EAT. The standardized mean difference (Hedges' g) and 95% confidence interval between interventions were computed using a random effects model. Ten studies (including 521 participants who had, on average, overweight/obesity) met all inclusion criteria. Interventions were supervised and lasted 2 to 16 weeks (≥3 sessions·per week). Exercise significantly reduced EAT (g = 0.82 [0.57-1.07]) irrespective of the duration of the intervention or the EAT imaging assessment method. Exercise benefits were separately confirmed for endurance (six studies, n = 287; g = 0.83 [0.52-1.15]) but not for resistance exercise training (due to insufficient data for quantitative synthesis). It was not possible to compare the effect of high-intensity interval training (HIIT) versus moderate-intensity continuous training (two studies, one reporting higher benefits with HIIT and the other no differences). Physical exercise interventions-particularly endurance training, with further evidence needed for other exercise modalities-appear as an effective strategy for reducing EAT in individuals with overweight/obesity, which supports their implementation for cardiovascular risk reduction.

Exercise Training and Neurodegeneration in Mitochondrial Disorders: Insights From the Harlequin Mouse

Aim

Cerebellar neurodegeneration is a main phenotypic manifestation of mitochondrial disorders caused by apoptosis-inducing factor (AIF) deficiency. We assessed the effects of an exercise training intervention at the cerebellum and brain level in a mouse model (Harlequin, Hq) of AIF deficiency.

Methods

Male wild-type (WT) and Hq mice were assigned to an exercise (Ex) or control (sedentary [Sed]) group (n = 10-12/group). The intervention (aerobic and resistance exercises) was initiated upon the first symptoms of ataxia in Hq mice (∼3 months on average) and lasted 8 weeks. Histological and biochemical analyses of the cerebellum were performed at the end of the training program to assess indicators of mitochondrial deficiency, neuronal death, oxidative stress and neuroinflammation. In brain homogenates analysis of enzyme activities and levels of the oxidative phosphorylation system, oxidative stress and neuroinflammation were performed.

Results

The mean age of the mice at the end of the intervention period did not differ between groups: 5.2 ± 0.2 (WT-Sed), 5.2 ± 0.1 (WT-Ex), 5.3 ± 0.1 (Hq-Sed), and 5.3 ± 0.1 months (Hq-Ex) (p = 0.489). A significant group effect was found for most variables indicating cerebellar dysfunction in Hq mice compared with WT mice irrespective of training status. However, exercise intervention did not counteract the negative effects of the disease at the cerebellum level (i.e., no differences for Hq-Ex vs. Hq-Sed). On the contrary, in brain, the activity of complex V was higher in both Hq mice groups in comparison with WT animals (p < 0.001), and post hoc analysis also revealed differences between sedentary and trained Hq mice.

Conclusion

A combined training program initiated when neurological symptoms and neuron death are already apparent is unlikely to promote neuroprotection in the cerebellum of Hq model of mitochondrial disorders, but it induces higher complex V activity in the brain.

Tailored exercise is safe and beneficial for acutely hospitalised older adults with COPD

Exercise rehabilitation programs have proven to increase exercise capacity and quality of life (QoL) in hospitalised patients with COPD. However, controversy exists as to the actual safety and effectiveness of this type of intervention We assessed the effects of an individualised exercise program on the functional capacity of acutely hospitalised older adults with COPD (as assessed with Barthel index and physical performance (Short Physical Performance Battery [SSPB]). Depression and QoL indicators, as well as serum C-reactive protein [CRP] and red blood cell distribution width [RDW] were also determined. Exercise-related side effects and incidence of readmission and mortality at 3 and 12-month–follow-up were also reported. We used the intention-to-treat approach. Of the 370 patients initially included in the RCT (11), 86 with COPD were identified (40 and 46 for the control and intervention group, respectively. The median length of stay was 8d (interquartile range, 4) for both groups. The exercise intervention improved all functional and physical performance-related outcomes (Barthel index, SPPB, 1RM leg strength) as well as depression and QoL scores, but no significant changes were found for CRP or RDW. No side effects associated were noted with the exercise sessions. No between-group differences were found for the incidence of readmission at 3 or 12-month follow-up; or for the incidence of mortality at 3 or 12-month follow-up. Our findings add to the existing limited literature supporting the benefits and safety of early rehabilitation programs in acutely hospitalised, older patients with COPD. Of note, the fact that our results were found in very older people (87 years on average) strengthens the potential safety of this type of interventions.

Exercise Reduces Ambulatory Blood Pressure in Patients With Hypertension: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Background Although exercise training reduces office blood pressure (BP), scarcer evidence is available on whether these benefits also apply to ambulatory blood pressure (ABP), which is a stronger predictor of cardiovascular disease and mortality. The present study aims to assess the effects of exercise training on ABP in patients with hypertension based on evidence from randomized controlled trials. Methods and Results A systematic search of randomized controlled trials on the aforementioned topic was conducted in PubMed and Scopus (since inception to April 1, 2020). The mean difference between interventions (along with 95% CI) for systolic BP and diastolic BP was assessed using a random-effects model. Sub-analyses were performed attending to (1) whether participants were taking antihypertensive drugs and (2) exercise modalities. Fifteen studies (including 910 participants with hypertension) met the inclusion criteria. Interventions lasted 8 to 24 weeks (3-5 sessions/week). Exercise significantly reduced 24-hour (systolic BP, -5.4 mm Hg; [95% CI, -9.2 to -1.6]; diastolic BP, -3.0 mm Hg [-5.4 to -0.6]), daytime (systolic BP, -4.5 mm Hg [-6.6 to -2.3]; diastolic BP, -3.2 mm Hg [-4.8 to -1.5]), and nighttime ABP (systolic BP, -4.7 mm Hg [-8.4 to -1.0]; diastolic BP, -3.1 mm Hg [-5.3 to -0.9]). In separate analyses, exercise benefits on all ABP measures were significant for patients taking medication (all P<0.05) but not for untreated patients (although differences between medicated and non-medicated patients were not significant), and only aerobic exercise provided significant benefits (P<0.05). Conclusions Aerobic exercise is an effective coadjuvant treatment for reducing ABP in medicated patients with hypertension.

Slackline Training in Children with Spastic Cerebral Palsy: A Randomized Clinical Trial

Objective: To assess whether a slackline intervention program improves postural control in children/adolescents with spastic cerebral palsy (CP). Design: Randomized controlled trial. Setting: Patients’ association. Participants: Twenty-seven children/adolescents with spastic CP (9–16 years) were randomly assigned to a slackline intervention (n = 14, 13 ± 3 years) or control group (n = 13, 12 ± 2 years). Intervention: Three slackline sessions per week (30 min/session) for 6 weeks. Main outcome measures: The primary outcome was static posturography (center of pressure—CoP—parameters). The secondary outcomes were surface myoelectrical activity of the lower-limb muscles during the posturography test and jump performance (countermovement jump test and Abalakov test). Overall (RPE, >6–20 scale) rating of perceived exertion was recorded at the end of each intervention session. Results: The intervention was perceived as “very light” (RPE = 7.6 ± 0.6). The intervention yielded significant benefits on static posturography (a significant group by time interaction on Xspeed, p = 0.006) and jump performance (a significant group by time interaction on Abalakov test, p = 0.015). Conclusions: Slackline training improved static postural control and motor skills and was perceived as non-fatiguing in children/adolescents with spastic CP.

Physical exercise effects on metastasis: a systematic review and meta-analysis in animal cancer models

Physical exercise is considered a well-tolerated adjuvant therapy to mitigate cancer-related side effects, but its impact on metastasis is unclear. The present systematic review and meta-analysis aimed to summarize the evidence on the effects of exercise on metastasis in animal cancer models. A systematic search was conducted to identify controlled studies in animals analyzing the impact of exercise interventions on any marker of metastasis incidence or severity. The pooled mean differences (PMD) were calculated for those endpoints for which a minimum of three studies used the same assessment method. We also calculated the pooled odds ratio (OR) of metastases. Twenty-six articles were included in the systematic review, of which 12 could be meta-analyzed. Exercise training in murine cancer models did not significantly modify the number of metastatic foci (PMD = - 3.18; 95% confidence interval [CI] - 8.32, 1.97; p = 0.23), the weight of metastatic tumors (PMD = - 0.03; 95% CI - 0.10, 0.04; p = 0.41), or the risk of developing metastasis (OR = 0.64; 95% CI 0.10, 4.12; p = 0.64). These findings suggest that exercise has no overall influence on any marker of cancer metastasis incidence or severity in animal models. However, the wide methodological heterogeneity observed between studies might be taken into account and the potential exercise effects on metastasis development remain to be determined in pediatric tumors.

Isometric Strength Measures are Superior to the Timed Up and Go Test for Fall Prediction in Older Adults: Results from a Prospective Cohort Study

Background

Isometric strength measures and timed up and go (TUG) tests are both recognized as valuable tools for fall prediction in older adults. However, results from direct comparison of these two tests are lacking. We aimed to assess the potential of isometric strength measures and the different modalities of the TUG test to detect individuals at risk of falling.

Methods

This is a prospective cohort study including 24 community-dwelling older adults (≥65 years, 19 females, 88±7 years). Participants performed three variations of the TUG test (standard, counting and holding a full cup) and three isometric strength tests (handgrip, knee extension and hip flexion) at several time points (at baseline and every ~6 weeks) during a one-year follow-up. The association between these tests and the incidence of falls during the follow-up was assessed.

Results

Twelve participants out of 24 participants experienced falls during the follow-up. Fallers showed a significantly lower handgrip strength (-5.7 kg, 95% confidence interval: -10.4 to -1.1, p=0.019) and knee extension strength (-4.9 kg, -9.6 to -0.2, p=0.042) at follow-up, while no significant differences were found for any TUG variation.

Conclusions

Handgrip and knee extension strength measures - particularly when assessed regularly over time - have the potential to serve as a simple and easy tool for detecting individuals at risk of falling as compared to functional mobility measures (ie, TUG test).

Perspective: Ketone Supplementation in Sports-Does It Work?

Oral ketone supplements have gained popularity in recent years. There is biological rationale for a potential ergogenic effect of this type of supplement, as they might not only alter muscle fuel preference during exercise (and promote glycogen sparing, with potential benefits for endurance performance) but also favor cognition performance during exertion or muscle glycogen synthesis after exercise. However, as discussed in this Perspective, evidence to date does not support a benefit of acute ketone supplementation on sports performance, cognition, or muscle recovery [although further research with long-duration exercise (i.e., >60 min), is needed], and the evidence for chronic supplementation is sparse. In addition, acute intake of ketone supplements might be associated with gastrointestinal symptoms, and further research is warranted on the long-term safety of repeated use of ketone supplements. In summary, there is currently insufficient evidence to support the overall effectiveness of ketone supplements in sports.

Lifestyle interventions for the prevention and treatment of hypertension

Hypertension affects approximately one third of the world's adult population and is a major cause of premature death despite considerable advances in pharmacological treatments. Growing evidence supports the use of lifestyle interventions for the prevention and adjuvant treatment of hypertension. In this Review, we provide a summary of the epidemiological research supporting the preventive and antihypertensive effects of major lifestyle interventions (regular physical exercise, body weight management and healthy dietary patterns), as well as other less traditional recommendations such as stress management and the promotion of adequate sleep patterns coupled with circadian entrainment. We also discuss the physiological mechanisms underlying the beneficial effects of these lifestyle interventions on hypertension, which include not only the prevention of traditional risk factors (such as obesity and insulin resistance) and improvements in vascular health through an improved redox and inflammatory status, but also reduced sympathetic overactivation and non-traditional mechanisms such as increased secretion of myokines.

Obesity can offset the cardiometabolic benefits of gestational exercise

Pregnancy exercise can prevent excessive gestational weight gain (EGWG), gestational diabetes mellitus (GDM) and hypertension (GH), but inter-individual variability has not been explored. We aimed to analyze the prevalence--and potential sociodemographic and medical predictors of--non-responsiveness to gestational exercise, and the association of non-responsiveness with adverse pregnancy outcomes. Among 688 women who completed a supervised light-to-moderate intensity exercise program (three ~1-h sessions/week including aerobic, resistance, and pelvic floor muscle training) until near-term, those who showed EGWG, GDM or GH were considered 'non-responders'. A low prevalence of non-responders was observed for GDM (3.6%) and GH (3.4%), but not for EGWG (24.2%). Pre-pregnancy obesity was the strongest predictor of non-responsiveness for GH (odds ratio 8.40 [95% confidence interval 3.10-22.78] and EGWG (5.37 [2.78-10.39]), whereas having a highest education level attenuated the risk of being non-responder for GDM (0.10 [0.02-0.49]). Non-responsiveness for EGWG was associated with a higher risk of prolonged labor length, instrumental/cesarean delivery, and macrosomia, and of lower Apgar scores. No association with negative delivery outcomes was found for GDM/GH. In summary, women with pre-pregnancy obesity might require from additional interventions beyond light-to-moderate intensity gestational exercise (e.g., diet and/or higher exercise loads) to ensure cardiometabolic benefits.

Exercise benefits on Alzheimer's disease: State-of-the-science

Although there is no unanimity, growing evidence supports the value of regular physical exercise to prevent Alzheimer's disease as well as cognitive decline in affected patients. Together with an introductory summary on epidemiological evidence, the aim of this review is to summarize the current knowledge on the potential biological mechanisms underlying exercise benefits in this condition. Regular physical exercise has proven to be beneficial for traditional cardiovascular risk factors (e.g., reduced vascular flow, diabetes) involved in the pathogenesis of Alzheimer's disease. Exercise also promotes neurogenesis via increases in exercise-induced metabolic factors (e.g., ketone bodies, lactate) and muscle-derived myokines (cathepsin-B, irisin), which in turn stimulate the production of neurotrophins such as brain-derived neurotrophic factor. Finally, regular exercise exerts anti-inflammatory effects and improves the brain redox status, thereby ameliorating the pathophysiological hallmarks of Alzheimer's disease (e.g., amyloid-β deposition). In summary, physical exercise might provide numerous benefits through different pathways that might, in turn, help prevent risk and progression of Alzheimer's disease. More evidence is needed, however, based on human studies.

Time to Exhaustion at the Respiratory Compensation Point in Recreational Cyclists

The time to exhaustion (t_lim) at the respiratory compensation point (RCP) and whether a physiological steady state is observed at this workload remains unknown. Thus, this study analyzed t_lim at the power output eliciting the RCP (t_lim at RCP), the oxygen uptake (VO₂) response to this effort, and the influence of endurance fitness. Sixty male recreational cyclists (peak oxygen uptake [VO_2peak] 40–60 mL∙kg∙min⁻¹) performed an incremental test to determine the RCP, VO_2peak, and maximal aerobic power (MAP). They also performed constant-load tests to determine the t_lim at RCP and t_lim at MAP. Participants were divided based on their VO_2peak into a low-performance group (LP, n = 30) and a high-performance group (HP, n = 30). The t_lim at RCP averaged 20 min 32 s ± 5 min 42 s, with a high between-subject variability (coefficient of variation 28%) but with no differences between groups (p = 0.788, effect size = 0.06). No consistent relationships were found between the t_lim at RCP and the different fitness markers analyzed (RCP, power output (PO) at RCP, VO_2peak, MAP, or t_lim at MAP; all p > 0.05). VO₂ remained steady overall during the t_lim test, although a VO₂ slow component (i.e., an increase in VO₂ >200 mL·min⁻¹ from the third min to the end of the tests) was present in 33% and 40% of the participants in HP and LP, respectively. In summary, the PO at RCP could be maintained for about 20 min. However, there was a high between-subject variability in both the t_lim and in the VO₂ response to this effort that seemed to be independent of fitness level, which raises concerns on the suitability of this test for fitness assessment.

Reply: Letter to the Editor: Exercise Interventions and Cardiovascular Health in Childhood Cancer: A Meta-Analysis

Dear EditorWe sincerely appreciate the nice comments by Drs. P.V. da Costa Ghignatti and R. Pereira de Lima 1 concerning our recent meta-analysis assessing the effects of physical exercise interventions on cardiovascular endpoints in childhood cancer survivors 2. They are quite right to remain that even non-significant improvements in cardiorespiratory fitness (CRF) might be clinically relevant. Indeed, we still do not know if CRF increments of a theoretically low magnitude (i. e., <1 metabolic equivalent) might have a prognostic value in the context of pediatric cancer and treatment-associated cardiotoxicity. We also agree that unsupervised exercise interventions are unlikely to be as effective as tailored programs, especially because the latter allow for intensity to being adequately controlled and thus gradually increased. It is indeed our opinion, after long years of experience working with children with cancer as well as with other debilitated clinical populations, that there is always room for physiological improvement and ideally loads should be gradually improved instead of remaining stable.

Effects of exercise interventions on the functional status of acutely hospitalised older adults: A systematic review and meta-analysis

BACKGROUND

Acute hospitalisation can have adverse effects in older adults, notably functional decline. We aimed to summarize evidence on the effects of exercise interventions in acutely hospitalised older adults.

METHODS

Relevant articles were systematically searched (PubMed, Web of Science, Rehabilitation & Sports Medicine Source, and EMBASE) until 19^th March 2020. Randomized controlled trials (RCTs) of in-hospital exercise interventions versus usual care conducted in older adults (>60yrs) hospitalised for an acute medical condition were included. Methodological quality of the studies was assessed with the PEDro scale. Primary outcomes included functional independence and physical performance. Intervention effects were also assessed for other major outcomes (length of hospital stay, incidence of readmission, and mortality). A meta-analysis was conducted when ≥3 studies analysed the same outcome.

RESULTS

Fifteen studies from 12 RCTs (n = 1748) were included. Methodological quality of the studies was overall high. None of the studies reported any adverse event related to the intervention. Exercise interventions improved functional independence at discharge (standardized mean difference [SMD] = 0.64, 95% confidence interval = 0.19-1.08) and 1-3 months post-discharge (SMD = 0.29, 95%CI = 0.13-0.43), as well as physical performance (SMD = 0.57, 95%CI = 0.18-0.95). No between-group differences were found for length of hospital stay or risk of readmission or mortality (all p > 0.05).

CONCLUSIONS

In-hospital supervised exercise interventions seem overall safe and effective for improving - or attenuating the decline of - functional independence and physical performance in acutely hospitalised older adults. The clinical relevance of these findings remains to be confirmed in future research.