Despite broad recognition of IPA as an important aspect of physical activity, there remains a need for greater clarity concerning its behavioral scope and the influence of intentionality on its classification. Traditionally, many studies have characterized IPA as unstructured, unintentional, and not specifically aimed at exercise or health improvement [10]. In recent years, however, growing evidence on the health benefits of IPA has influenced physical activity guidelines. For example, the World Health Organization moved away from recommending “at least 10 continuous minutes” of activity toward acknowledging that “any amount of physical activity is better than none, and the more, the better” [14]. This transition reflects an important evolution: IPA is now promoted intentionally for health, even though it was originally conceived as a non-purposeful activity. Terminological variations persist in the literature, where phrases such as “incidental physical activity”, “non-exercise activity thermogenesis”, and “vigorous incidental physical activity” are often used alongside “activities of daily living” [10]. While these terms emphasize different aspects, the fundamental idea of IPA—non-structured movement integrated into everyday life—remains consistently acknowledged. Consequently, the challenge is not in defining IPA itself but in operationalizing its various subtypes, particularly distinguishing between unintentional and intentionally integrated IPA.

To effectively capture intentionality in practice, various approaches can be utilized in both research and public health settings. In epidemiological surveys, questionnaires can assess intent by asking questions such as, “Do you typically take the stairs to increase your physical activity?” or “How often do you opt for active transportation (e.g., walking or cycling) for health reasons?” In device-based assessments, such as those using accelerometers, the volume and intensity of activity can be objectively measured during brief intervals, with intentionality further inferred through supplementary tools like ecological momentary assessment. For example, smartphone prompts could inquire, “Was this activity performed for exercise or health purposes?” However, in public health messaging, the distinction between intentional and unintentional IPA is often less critical, as the primary focus is on encouraging behavioral integration irrespective of the initial motivation. Messages like “Choose stairs whenever possible” promote intentional action without emphasizing underlying motivation.

We suggest defining IPA based not on intentionality but on its behavioral context: as unstructured movements inherent to daily routines, including household chores, active commuting, and occupational tasks. This perspective eliminates ambiguity and aligns with modern health strategies. For instance, whether stair climbing occurs due to a broken elevator (unintentional) or a health-driven choice (intentional), it is still classified as IPA. This cohesive definition enhances communication and encourages individuals to consciously incorporate more IPA into their daily lives, transforming incidental movements into their daily lives, transforming opportunities for improving health.

IPA is operationally distinguished from structured exercise by its integration into daily routines through short, intermittent bouts interspersed with rest or low-intensity movement [15]. In alignment with the Compendium of Physical Activities [16], IPA has been categorized into various domains, including household tasks, gardening, ambulation, and cycling [17].

The existing literature presents various classifications and stratifications of IPA, with specific criteria outlined in Table 1 (Ref. [8, 9, 10, 11, 12]).

These classifications are typically based on objective metrics such as accelerometer-derived milligravity thresholds [8], step cadence [10], bout duration, metabolic equivalent of task (MET) thresholds, cardiorespiratory demands, and neuromuscular engagement [8]. Activities are categorized into several types: sedentary behavior, standing utilitarian tasks, walking, and high-energy activities like running. To pinpoint specific activities and their corresponding intensity levels, researchers frequently use a validated two-stage random forest classifier, which boasts an overall accuracy of 86.4% [11, 18]. Based on these criteria, IPA can be stratified into three distinct categories, as shown in Fig. 1 (Ref. [9]) and Table 2.

Fig. 1.

Classification of IPA. IPA can be classified into three categories. Light intensity IPA (LIPA): characterized by MET values 3.0 or step cadence $\le$19 steps/minute [9], such as leisurely walking, light stretching, or light standing tasks (e.g., washing dishes, folding laundry). Moderate intensity IPA (MIPA): defined by METs 3.0–5.9 or cadence 20–39 steps/minute [9], including brisk walking for transportation, gardening, carrying light loads, cycling, or climbing stairs. Vigorous intensity IPA (VIPA): Vigorous-intensity activities ($\ge$6 METs) performed in ultrashort bursts ($\le$1–3 minutes), exemplified by vigorous intermittent lifestyle physical activity ($\le$1-minute bouts, e.g., sprinting upstairs) or moderate-to-vigorous intermittent lifestyle physical activity (MV-ILPA, $\le$3-minute bouts, e.g., carrying groceries). The diagram was drawn by Figdraw. Abbreviations: IPA, incidental physical activity; LIPA, light intensity IPA; MET, metabolic equivalent of task; MIPA, Moderate intensity IPA; MV-ILPA, moderate-to-vigorous intermittent lifestyle physical activity; VIPA, vigorous intensity IPA.

Light intensity IPA (LIPA): Characterized by MET values 3.0 or step cadence $\le$19 steps/minute [10], such as leisurely walking, light stretching, or light standing tasks (e.g., washing dishes, folding laundry), with energy expenditure between 30–125 milligravities [8]. LIPA induces minimal increases in heart rate and oxygen uptake (VO₂) without significant lactate accumulation [8, 19]. It is characterized by energy expenditure below 40% of HR reserve and is frequently integrated into daily activities as unstructured movement. These movements mainly serve to break up sedentary patterns but do not provide enough intensity to induce substantial cardiometabolic adaptations [9, 20]. They are often fragmented into brief, intermittent bouts [21].

Moderate intensity IPA (MIPA): Defined by METs 3.0–5.9 or cadence 20–39 steps/minute [10], including brisk walking for transportation, gardening, carrying light loads, cycling, or climbing stairs, with energy expenditure between 125–400 milligravities [8], achieving 40–60% of heart rate reserve or 64–76% of maximal heart rate [14]. This intensity boosts aerobic capacity, enhances metabolic efficiency, and is associated with significant reductions in both systolic blood pressure and low-density lipoprotein cholesterol levels [8]. Accumulating $\ge$21.8 minutes/day of such activities enhances cardiorespiratory fitness and metabolic health [9, 14].

Vigorous intensity IPA (VIPA): Vigorous-intensity activities ($\ge$6 METs) performed in ultrashort bursts ($\le$1–3 minutes), exemplified by vigorous intermittent lifestyle physical activity ($\le$1-minute bouts, e.g., sprinting upstairs) or moderate-to-vigorous intermittent lifestyle physical activity (MV-ILPA, $\le$3-minute bouts, e.g., carrying groceries), with energy expenditure $>$400 milligravities [8]. VIPA is episodic but confers disproportionate metabolic benefits [8], and demonstrates pronounced dose-response associations with health outcomes [22], driving VO₂ to $>$60% of peak levels and stimulating anaerobic glycolysis [23]. It triggers quick cardiovascular changes, such as enhanced myocardial oxygen consumption and decreased arterial stiffness. However, it necessitates vigilant monitoring because of the increased hemodynamic stress involved [8]. Even minimal durations (e.g., 4.1 minutes/day of VIPA) yield significant cardiovascular protection [21, 24].

Emerging epidemiological evidence suggests that IPA, even at light intensity, offers substantial cardiovascular protection across various populations. Notably, the benefits of IPA tend to increase significantly with greater intensity (Table 3, Ref. [8, 9, 11, 25]). This section systematically examines the cardiovascular protective effects of IPA through recent device-measured data and clinical studies.

Objective monitoring studies utilizing wearable devices demonstrate that even sporadic bouts of vigorous intermittent lifestyle physical activity, e.g., stair climbing, provide clinically significant health benefits. This evidence supports the adoption of “lifestyle-integrated” preventive approaches [25]. Current World Health Organization recommendations (75–150 minutes/week of moderate-to-vigorous activity) [14] can be effectively adapted to IPA frameworks.

Stamatakis et al.’s analysis [11] of UK Biobank data revealed that both MIPA and VIPA significantly lower the risk of major adverse cardiovascular events (MACE) and CVDs mortality in middle-aged and older adults who do not engage in regular exercise. The findings indicated that a median daily duration of 23.8 min of MIPA or 4.6 minutes of VIPA corresponded with a 40–50% reduction in MACE risk and a 50% decrease in CVD mortality [11]. The study established novel inter-intensity “health equivalence”: 1 minute of VIPA corresponded to 2.8 (for MACE) to 3.4 (for CVD mortality) minutes of MIPA for CVD outcomes, and 34.7–48.5 minutes of light IPA (LIPA) [11]. These findings challenge traditional MET-based assumptions (presumed 1:2 VIPA: MIPA ratio) and emphasize intensity-specific cardioprotective mechanisms [26]. Further investigations revealed that brief VIPA bouts ($>$4.1 min/day) negated sedentary-associated MACE risk ($>$11.4 h/day) in non-exercisers [9], while accumulating 31–65 min/day MVPA or 26–52 min/day MV-ILPA neutralized sedentary-related mortality [22, 24].

In populations with pre-existing CVDs, we observed an inverse association between the IPA volume and all-cause mortality. The mortality risk decreased by 50% with $\ge$1380 min/week LIPA (hazard ratio (HR): 0.63; 95% confidence interval (CI): 0.51–0.79), whereas $\ge$155 min/week MIPA yielded a 58% reduction (HR: 0.42) [8]. Notably, $\ge$45 min/week VIPA reduced CVD-specific mortality by 54% versus inactivity [8]. According to population-attributable fraction (PAF) estimates, inadequate engagement in VIPA was responsible for 43% of preventable CVD deaths, markedly exceeding the proportions associated with insufficient moderate-intensity (18.1%) and light-intensity (9.8%) activity [8]. VIPA demonstrated superior mortality risk reduction (PAFs up to 52.1%) compared to longer-duration moderate activities, likely mediated through rapid metabolic adaptations [21, 27]. Analysis of the objective measurements in an accelerometer study further revealed that the light-intensity stepping (40 steps/min) reduced CVD mortality risk (HR 0.90 per 10% daily increase), while higher cadences (peak-30 cadence) conferred greater protection (HR 0.86) in adults aged 40–79 without baseline CVDs [25].

Besides its systemic benefits, physical activity has been shown to elicit highly individualized, intensity-dependent hemorheological adaptations [28]. These include improved red blood cell flexibility and reduced aggregation, lowered blood viscosity, and modified plasma levels of fibrinogen, albumin, and other rheologically active components [28]. Exercise also expands plasma volume and total blood volume, particularly in trained individuals [29], and induces functional and structural endothelial adaptations—though response thresholds for markers such as endothelin-1 are person-specific [30]. Additional benefits involve lowered blood pressure via upregulation of nitric oxide and prostaglandins [31, 32], and hypoxia-induced improvements in blood flow properties [33, 34]. These micro-level changes in hematology and hemorheology, influenced by the frequency, intensity, and duration of physical activity, are fundamental to the cardiovascular benefits associated with regular exercise [28].

The cardiovascular advantages of IPA arise from interconnected biological mechanisms. Improved endothelial function, indicated by increased nitric oxide bioavailability at all IPA intensities, mitigates atherogenic drivers, such as oxidative stress and inflammatory responses [15, 35]. This vascular improvement is accompanied by stabilized autonomic regulation, in which augmented parasympathetic tone and heart rate variability reduce arrhythmia susceptibility [36]. At the metabolic level, IPA stimulates mitochondrial oxidative phosphorylation efficiency—particularly in fatty acid metabolism—through AMP-activated protein kinase/Peroxisome proliferator-activated receptor gamma coactivator 1-alpha (AMPK/PGC-1$\alpha$) signaling cascades that upregulate carnitine palmitoyltransferase I (CPT1) expression and adenosine triphosphate (ATP) synthesis, counteracting metabolic rigidity in cardiac tissue [8, 15, 37]. Furthermore, regular daily activity, such as that achieved through IPA, is crucial for maintaining metabolic health by enhancing postprandial fat metabolism [38] and preventing the resistance to metabolic improvements that can follow periods of inactivity [39]. In addition, IPA inhibits systemic inflammation via intensity-dependent mechanisms: vigorous IPA primarily boosts endothelial nitric oxide synthase (eNOS) activation to reduce arterial stiffness, whereas moderate IPA decreases the NAIP, CIITA, HET-E, and TP1 (NACHT), Leucine-Rich Repeat (LRR), and PYD domains-containing protein 3 (NLRP3) inflammasome activity ($\downarrow$Interleukin-1 beta (IL-1$\beta$), $\downarrow$Tumor necrosis factor-alpha (TNF-$\alpha$)) and amplifies endogenous antioxidant defenses ($\uparrow$Superoxide dismutase (SOD), $\uparrow$Glutathione (GSH)) [15, 35].

Clinically, these integrated pathways result in significant cardiovascular enhancements. Engaging in moderate-to-vigorous intensity physical activity can lead to a reduction in systolic blood pressure by 5 to 8 mmHg and a decrease in Low-Density Lipoprotein (LDL) cholesterol by 10 to 15% among sedentary individuals. This is achieved through the optimization of lipid metabolism and the enhancement of the nitric oxide pathway [15, 37]. Intermittent high-intensity protocols significantly improve the efficiency of myocardial oxygen utilization and reduce arterial stiffness. These combined effects help lower the risks associated with hypertension and atherosclerosis [15, 40].

IPA provides an effective approach to overcoming the obstacles linked to structured exercise, such as limited time and the requirement for specialized equipment. It presents accessible and practical movement options tailored for sedentary groups, including office workers, older adults, and those with CVDs [41, 42].

Core strategies for implementation include integrating activities such as stair climbing, active breaks, and household chores into daily routines [9, 14]. Clinicians can encourage patients to adopt several practical strategies to increase their physical activity. These include parking further away from their destinations, opting for stairs rather than elevators for trips of three floors or less, and scheduling “walking meetings” or taking active breaks every 30 to 60 minutes during prolonged periods of sitting. Additionally, engaging in household chores like vacuuming or gardening at a brisk pace. The WHO’s recommendation of 150 minutes of moderate-to-vigorous physical activity (MVPA) per week can be achieved through accumulated incidental physical activity (IPA). For instance, this may include 10 minutes of brisk walking for daily transport (moderate-intensity IPA), 15 minutes of vigorous gardening (vigorous-intensity IPA), and 5 minutes of stair climbing (vigorous-intensity IPA) distributed throughout the week. This lifestyle-integrated approach makes physical activity goals more attainable in everyday life.

While a minimum of 45 minutes per week of VIPA correlates with optimal mortality benefits, it is important to exercise caution when recommending VIPA to patients with unstable CVDs due to its potential arrhythmogenic effects [8, 43]. Therefore, promoting IPA requires tiered recommendations based on the principle of “graded health benefits”. The practical application of IPA should focus on personalized prescriptions and risk stratification. For example, frail individuals or those with advanced CVDs should receive customized adjustments to their programs to prevent overexertion [44]. For high-risk groups (e.g., older adults, individuals with metabolic syndrome, stable CVD), pre-participation cardiovascular screening (e.g., history, physical exam, Electrocardiogram (ECG), or stress testing for silent ischemia) is recommended before engaging in VIPA [8, 15, 23, 45]. Based on sports cardiology guidelines [23], initial intensity should be moderated (e.g., staying below 85% of age-predicted maximum heart rate, Borg Scale perceived exertion 15/20) and progressed gradually. Supervised cardiac rehabilitation programs are the gold standard and essential starting points for these populations [8], where the benefit-risk ratio of unsupervised VIPA can be carefully evaluated.

The safe implementation of IPA requires a careful and gradual transition from low-intensity to high-intensity exercise sessions. It is crucial to monitor perceived exertion in real-time, using tools such as the Borg Scale and hemodynamic parameters. This approach helps to mitigate the risks of developing arrhythmias or experiencing exertional angina during physical activity [8, 15, 46]. The quantification of sporadic, low-volume IPA bouts presents a challenge, as self-report questionnaires (e.g., IPEQ) are prone to overestimating activity intensity [25, 47], while wrist-worn accelerometers may underestimate certain activities, such as cycling or weight-bearing tasks [9, 24, 48]. Therefore, multimodal assessments integrating accelerometry, heart rate monitoring, and machine learning classifiers are essential to enhance the accuracy of IPA measurement [49]. Clinicians should prioritize wearable technologies for personalized activity prescriptions [50].

To achieve sustained long-term engagement, time-efficient approaches such as “exercise snacks” (e.g., 5-minute stair climbing) are recommended [15, 19]. Furthermore, AI-driven applications for real-time feedback may also be used to enhance adherence [8]. Environmental interventions, such as stair-use prompts, can increase participation by 12–15% [51], and urban planning initiatives that emphasize mixed-use zoning and pedestrian connectivity may potentially enhance active transportation [52]. For sedentary populations, vigorous intermittent lifestyle physical activity and workplace interventions are effective strategies to integrate movement into daily routines [53].

Current evidence highlighting the cardiovascular benefits of IPA largely stems from studies conducted on non-exercising adults within the UK Biobank. However, this evidence base has limitations due to the cohort’s lack of representativeness, which may skew effect estimates. Notably, over 90% of participants identify as White, contrasting sharply with the more diverse general population. Additionally, the educational attainment within this cohort is significantly higher, with over 55% holding university degrees compared to approximately 27% nationally. Socioeconomic factors also play a role, as participants tend to live in less deprived areas and engage in healthier behaviours, likely leading to an attenuation of risk estimates and an overestimation of the protective effects of physical activity. Moreover, the cohort is predominantly older, with ages ranging from 40 to 79 at the time of recruitment, resulting in a lack of representation for younger and very elderly groups. The “healthy volunteer” effect further exacerbates this issue by excluding individuals with high genetic susceptibility, severe comorbidities, or adverse socioeconomic conditions. Consequently, these biases may result in an underestimation of risk associations and limit the generalizability of findings to more diverse, disadvantaged, or high-risk populations [24, 54]. Consequently, future research should prioritize longitudinal studies encompassing diverse demographic groups and further focus on refining tools for accurately measuring IPA [12].