"Flow is a scientific definition and Mihaly Csikszentmihalyi is the one who came up with that definition, but it's technically defined as an optimal state of consciousness where we feel our best and perform our best." - Steven Kotler [00:01:03]
"Peak performance is nothing more or less than getting our biology to work for us rather than against us." - Steven Kotler [00:03:44]
"Autonomy and attention are coupled systems in the brain, so you cannot maximize focus if you're not the one driving the bus." - []
Disclaimer: Orignal content owned by or sourced from third parties. It does not represent the views of 'Nuggets' platform or it's team. AI is used extensively across this platform including for summaries. Accuracy is not guaranteed, there can be mistakes. Any info or content on this platform is not a financial, legal, or investment advice. Do your own research. Refer for complete disclosures:- Terms of Use · Full Disclaimer
"When we play versus when we repeat the same thing with incremental improvement, we get way more neurochemicals. So deliberate play will outperform deliberate practice." - Steven Kotler [00:26:23]
"If you know your starts and your endings, you have a pattern recognition system for the brain—it will connect them." - Steven Kotler [00:38:00]
"As we transition into a flow state, there's a global release of nitric oxide... stress hormones are stripped from your system and replaced by performance-enhancing feel-good neurochemistry." - Steven Kotler [00:58:45]
"I want to be the greatest writer in the history of the universe... success is not a destination, it's a way of living." - Steven Kotler [01:05:09]
Speakers & Credentials
Shane Parrish (Host): Founder of Farnam Street (FS), host of The Knowledge Project Podcast, former intelligence officer, decision scientist, and author specializing in mental models, cognitive frameworks, and executive performance.
Steven Kotler (Guest): Executive Director of the Flow Research Collective, New York Times best-selling author (The Rise of Superman, Gnar Country, Stealing Fire, West of Jesus), journalist, and leading global authority on human peak performance, neurobiology, and flow state optimization.
1. Executive Summary
Flow is scientifically defined as an optimal state of consciousness where humans feel and perform at their absolute peak, characterized by total absorption and complete concentration [00:01:03].
Peak performance is not an abstract mystery; it is simply getting human biology and neurochemistry—primarily dopamine and norepinephrine—to work for us rather than against us [00:03:44].
Empirical data from the Flow Research Collective's Zero to Dangerous 8-week program shows a 73% boost in flow across 35,000 participants [00:04:34], while DARPA research indicates flow accelerates learning rates by 230% [00:24:41].
The ideal flow entry condition is the Challenge-Skills Balance, occurring when task difficulty exceeds existing skills by approximately 4% [00:10:19]; operating strictly within this 4% sweet spot prevents skill plateaus [00:12:38].
Human biology naturally aligns focus with 90-to-110-minute ultradian rhythm cycles [00:14:34], making structured focus blocks essential while batching communications to combat modern executive distraction (averaging 17-18 incoming communication channels) [00:13:43].
ADHD represents hyperflow rather than a focus deficit, driven by the brain's coupled autonomy-attention system [00:16:46]; individuals with ADHD can unlock peak focus by reframing tasks to align with intrinsic purpose [00:17:44].
Deliberate play (repetition with improvisation) significantly outperforms deliberate practice (repetition with incremental improvement) in all unbounded domains because higher neurochemical dumps tag experiences for long-term memory storage [00:25:05].
Human motivation scales along a precise stack: Curiosity (foundational dopamine) $\rightarrow$ Passion (intersection of multiple curiosities) $\rightarrow$ Purpose (passion linked to a cause, adding serotonin, oxytocin, and endorphins) [00:26:39].
Frustration during the "struggle phase" of learning overloads working memory/RAM, which is a required precursor for subsequent intuitive breakthroughs and flow entry [00:32:46].
Flow states induce a massive nitric oxide release that flushes stress hormones (cortisol) and resets nervous system homeostasis, serving as a powerful mechanism for overcoming burnout, PTSD, and autoimmune conditions like Lyme disease [00:58:45].
2. Chronological Table of Contents
[00:00:00] Introduction & Teaser: The Addictive Nature of Flow and DARPA's 230% Learning Acceleration
[00:28:20] Spite as a Motivator & Critic Management: Rebutting "The Body Keeps the Score"
[00:31:37] Rebutting Cal Newport & The 4-Stage Flow Cycle: Frustration as a Loading Mechanism
[00:35:20] The Brain as a Prediction Engine & The ROI of Reading: Stocking Pattern Recognition Systems
[00:41:54] The Learning Loop & Expert Interviewing: Moving Beyond Compressions & Seduction into Flow
[00:47:31] Metacognition, Josh Waitzkin & "Dark Hours": Emotion vs. Feeling and 4:00 AM Non-Time
[00:53:34] Lyme Disease, Autoimmune Healing & Flow Neurochemistry: Nitric Oxide and System Homeostasis
[01:04:11] Defining Personal Success & Competitive Ambition: Words in a Straight Line
3. Detailed Thematic Summary
Defining Flow & The 6 Core Characteristics
Mihaly Csikszentmihalyi scientifically defined flow as an optimal state of consciousness where individuals feel their best and perform their best [00:01:03]. It marks moments of total absorption where attention narrows strictly to the immediate task [00:01:15].
Flow is characterized by six distinct subjective experience components [00:01:37]:
Complete concentration on the task at hand [00:01:42].
Diminishment of the sense of self (loss of self-consciousness) [00:01:48].
Time distortion (time dramatically speeds up or slows down) [00:01:50].
Deep sense of control over circumstances normally uncontrollable (e.g., Michael Jordan describing the basketball hoop appearing as large as a hula hoop while in flow) [00:02:03].
Autotelic quality (the experience is euphoric and an end in itself) [00:02:14].
Flow represents the single most addictive psychological state on Earth, driving individuals to go to extreme lengths to re-experience it [00:02:20].
Neurobiological Mechanism & Evolutionary Origins
Evolution engineered flow as the primary biological vehicle for peak human performance [00:02:49]. Its evolutionary origins link directly to the runner's high and collective animal dynamics like flocking and mobbing behaviors in social mammals, birds, and insects [00:02:56].
Peak performance requires no mystical secret; it is strictly defined as getting shared neurobiology to work for us rather than against us [00:03:44].
While subjective goals differ between individuals, the underlying biological currency of motivation, energy, and drive is universally mediated by dopamine release [00:04:04].
Data from the Flow Research Collective's flagship 8-week Zero to Dangerous program (encompassing 35,000 participants) demonstrated a 73% average boost in measured flow [00:04:34]. This proves flow is highly trainable because neurobiological mechanisms are standardized across all humans [00:04:52].
Flow Triggers, Cognitive Load & Environmental Control
Flow follows focus; it emerges exclusively when 100% of attention is anchored in the present moment [00:05:18]. Scientists have identified 26 to 28 psychological, environmental, and interpersonal flow triggers [00:05:08].
Triggers function by altering neurochemistry—flushing norepinephrine, dopamine, or both into the brain—or by systematically reducing cognitive load [00:05:30].
Cognitive load represents the sum of information processed in working memory. Physical environment optimization (e.g., cleaning a desk before working) directly reduces cognitive load, allowing the brain to instantly reallocate conserved energy into attentional focus [00:05:42].
Primary Flow Activity & Overriding Burnout
A Primary Flow Activity is the baseline pursuit (often discovered in childhood, such as skiing, playing guitar, or backcountry hiking) that reliably triggers deep flow [00:06:22]. Globally, reading is the most common primary flow activity [00:09:33].
Adults routinely abandon their primary flow activities due to career and family responsibilities, which represents a critical physiological error for three key reasons [00:07:25]:
Flow is a trainable neural focusing skill. Engaging in flow on Sunday primes neural pathways for easier flow entry at work on Tuesday [00:07:38].
High anxiety blocks flow entry. Primary flow activities reset autonomic nervous system baseline, lowering baseline stress [00:08:05].
Flow overrides severe burnout, PTSD, depression, and addiction by providing neuroprotective rewiring (validated by lab research from Karina Feifer) [00:08:34].
Allocating just 2 to 4 hours per week to a primary flow activity is sufficient to maintain these high-performance biological benefits [00:09:07].
The Challenge-Skills Balance & The 4% Sweet Spot
The most prominent psychological flow trigger is the Challenge-Skills Balance [00:10:00]. Attention maximizes when task difficulty slightly outpaces current skill capability [00:10:08].
Mihaly Csikszentmihalyi and a Google mathematician calculated that the optimal sweet spot occurs when the challenge level exceeds skill level by exactly 4% [00:10:19].
Physiologically, this sweet spot sits on the Yerkes-Dodson curve between boredom (insufficient arousal) and anxiety (excessive arousal) [00:10:57]. High achievers (Type A personalities) tend to over-shoot this balance by taking on 50-60% skill gaps, which induces panic and destroys focus [00:11:22].
Setting properly structured hard goals provides an immediate 11% to 22% boost in baseline motivation [00:11:46]. However, those macro goals must be chunked down into micro-tasks fitting the 4% threshold [00:11:54].
Field testing on downhill mountain bikers (measuring precise jump sizes and trail features) proved that remaining consistently within the 4% window completely eliminates skill development plateaus [00:12:28].
Ultradian Focus Blocks & Muting Modern Distraction Channels
Distraction elimination is mandatory for flow. 20 years ago, executives managed 3 to 4 primary interruption channels (phone calls, email, physical door knocks); modern executives average 17 to 18 distinct incoming channels (Slack, WhatsApp, Notion, iMessage, etc.) [00:13:43].
High performers must wall off environment distractions, turn smartphones off, batch communications into designated morning/evening windows, and maintain only 1 emergency channel [00:14:10].
Human biology operates on ultradian rhythms: the 90-to-110-minute REM sleep cycle matches an equivalent awake-and-alert biological cycle [00:14:29]. The brain is genetically optimized to focus in 90-minute blocks [00:14:49].
Steven Kotler calibrates daily book writing targets to 500 words per day to fit the 4% sweet spot, dialing down to 300 words if sleep-deprived [00:15:46].
ADHD as Hyperflow: Autonomy & Task Reframing
Grounded in work with Harvard psychologist Ned Hallowell, ADHD is reclassified not as a focus deficiency, but as hyperflow and an evolutionary superpower [00:16:31]. The struggle is not focusing, but focusing on subjects lacking personal interest [00:16:46].
In the brain, autonomy and attention are tightly coupled neural systems [00:17:21]. Individuals cannot maximize attentional control without driving the outcome [00:17:30].
The core intervention for ADHD is task reframing: isolating the small percentage of an assigned task that builds a desired personal skill or aligns with core values (e.g., writing 5,000 words on data caves to study Wired magazine's narrative structure) [00:17:44].
Dopamine and norepinephrine surges during flow massively amplify pattern recognition (the brain's creative trigger) [00:19:44]. Because tangents feel "delicious" in flow, individuals with ADHD must police thoughts by writing down creative tangents to explore later without abandoning the core task [00:20:25].
Deliberate Play vs. Deliberate Practice & The Motivation Stack
DARPA research demonstrated that training individuals within flow states speeds up learning velocity by 230% [00:24:41].
Challenging Anders Ericsson's 10,000-hour deliberate practice rule (popularized by Malcolm Gladwell) [00:24:34], research shows deliberate practice (repetition with incremental improvement) works only in bounded, hyper-structured domains like mathematics or classical violin [00:25:26].
In all unbounded domains, Deliberate Play (repetition with improvisation) significantly outperforms deliberate practice [00:25:48]. Memory consolidation requires neurochemical tagging ("important, save for later"); play releases a far higher volume of neurochemicals than rigid repetition [00:25:57].
Biological human motivation builds sequentially across three tiers [00:26:39]:
Curiosity: Foundational motivator delivering small doses of dopamine [00:26:55].
Passion: Generated at the intersection of multiple curiosities (mapped by identifying 25 curiosities and finding overlaps via LLMs) [00:27:10].
Purpose: Formed by coupling passion to a cause larger than oneself. Purpose adds pro-social neurochemistry (serotonin, oxytocin, endorphins) on top of dopamine and norepinephrine [00:27:46].
Strategic Spite, Critic Management & Rebutting "The Body Keeps the Score"
Spite ("chip on the shoulder") functions as a potent away-from motivator (exemplified by Tom Brady) [00:28:40]. However, unchecked spite becomes toxic over time, as observed in Michael Jordan's post-career bitterness [00:29:10]. High performers must use "small-s spite" and know when to step away [00:29:45].
Engaging critics publicly wastes intellectual capital [00:30:04]. Kotler co-authored a scientific paper in Frontiers in Neuroscience titled "The Body Doesn't Keep the Score" as a direct scientific rebuttal to Bessel van der Kolk [00:30:18]. Rather than wasting energy arguing with critics on social media, researchers should simply publish further empirical data [00:30:40].
The 4-Stage Flow Cycle & The Power of Frustration (Struggle Phase)
Countering Cal Newport's concept of "Deep Work," deep work is functionally identical to flow state [00:32:16]. Flow is not a single light-switch event; it follows a mandatory 4-stage biological cycle: 1. Struggle, 2. Release, 3. Flow, 4. Recovery [00:32:26].
Stage 1 (Struggle) is an intense conscious loading phase. Research by Colleen Seifert (University of Michigan) proved that deep frustration overloads working memory/RAM, which is essential for triggering later intuitive breakthroughs and flow entry [00:32:53].
Kotler’s Nature paper ("Pathfinding: A Neurodynamical Account of Intuition") confirms that higher frustration during initial learning directly correlates with greater subsequent intuition [00:33:18].
Frustration is not a sign of failure or inadequacy; it is physiological confirmation of working memory saturation driving progress [00:34:00]. Learning requires norepinephrine (low levels = curiosity, high levels = anxiety) [00:34:41].
The Brain as a Prediction Engine & The ROI of Reading
The human brain operates fundamentally as a prediction engine designed to minimize environmental uncertainty and conserve caloric energy [00:35:28].
To optimize pattern recognition, high performers must continuously feed the system by reading a minimum of 25 pages per day [00:36:34]. Books represent the densest format of human knowledge [00:37:02].
Writer's block is caused by missing starting and ending reference points; when starting and ending parameters are clearly defined, the brain's internal pattern recognition automatically completes the connective narrative [00:37:42].
The Return on Investment (ROI) of Reading:
1,000-word blog post: Requires 5-8 minutes to read, delivering ~6 hours of single-author effort [00:40:43].
72,000-word book (e.g., Rise of Superman): Requires 6-7 hours to read, delivering 15 years of concentrated research and synthesis from hundreds of top minds [00:41:24].
Information Compression & Interviewing Mastery
Shane Parrish’s "Learning Loop" model: Experience $\rightarrow$ Reflection $\rightarrow$ Compression $\rightarrow$ Action [00:42:01]. Consuming second-hand compressions creates the illusion of knowledge, whereas true expertise requires experiencing the underlying variables [00:42:13].
Rules for interviewing world-class experts to extract pristine information [00:45:12]:
Conduct exhaustive pre-interview research (e.g., uncovering the patron saint of a Finnish vodka executive’s hometown) [00:45:27].
Question 1 must demonstrate detailed personal background knowledge [00:46:01].
Question 2 must demonstrate deep domain context (e.g., contrasting David Eagleman’s work in Incognito against past literature) [00:46:14].
Seduce the subject into interpersonal flow by comfortably dropping ego and asking them to "explain it like I'm four years old" [00:46:47].
Metacognition, "Dark Hours" & The 4:00 AM Non-Time
Peak learners like Josh Waitzkin (chess grandmaster and Tai Chi Push Hands champion) develop elite metacognition because errors in their fields yield immediate physical or competitive consequences [00:47:31].
Shane Parrish's "Dark Hours" theory: Peak performers hone skills in complete isolation (after hours or early morning) where failing carries zero public or professional cost [00:51:19].
Steven Kotler executes creative work during 3:30/4:00 AM to 7:00 AM "Non-Time" [00:51:58]. Early morning hours carry zero external obligations, permitting playful linguistic experimentation (such as spending 2 full hours refining a single sentence) [00:53:01].
Lyme Disease Recovery & The Neurochemistry of Healing
Kotler contracted Lyme disease from a tick bite in Long Island after returning from expeditions in Madagascar and the Sahara [00:54:12]. He was bedridden for 3 years, took Doxycycline for 1.5 years (causing stomach bleeding), saw cognitive function drop to 10%, lost memory, and became suicidal [00:54:24].
A friend forced him to go ocean surfing; popping up on a wave triggered a macro flow state featuring time dilation and an out-of-body experience [00:56:12]. Surfing regularly restored his functionality from 10% to 80% over 6 months [00:57:15]. He lost 41 lbs (dropping from 170 to 129 lbs) and lost 1 inch of height [01:00:37].
Host Shane Parrish also suffered severe Lyme disease: developed Bell's palsy (left facial paralysis), was misdiagnosed in the ER as having a heart attack, lost leg stability, and developed lockjaw before receiving antibiotics [01:01:05].
Biological mechanism of flow healing (supported by Herb Benson's The Breakout Principle) [00:58:21]: Entering flow triggers a massive systemic release of nitric oxide [00:58:45], which flushes stress hormones (cortisol) and replaces them with immune-boosting neurochemicals (dopamine, norepinephrine, serotonin) [00:59:08]. This resets autonomic nervous system homeostasis in patients with severe autoimmune conditions [00:59:26].
The Reference Vault
4. Core Frameworks & Mental Models
The 6 Core Characteristics of Flow [00:01:27]: The foundational psychological criteria defining flow state: (1) Complete concentration, (2) Action-awareness merger, (3) Diminished self-consciousness, (4) Time distortion, (5) Paradoxical sense of control, and (6) Autotelic (intrinsic motivation) state.
The Challenge-Skills Balance & 4% Rule [00:10:19]: Attentional focus optimizes when task difficulty exceeds skill capability by approximately 4%. Situated on the Yerkes-Dodson physiological curve between boredom and anxiety.
The 4-Stage Flow Cycle [00:32:26]: Flow is not a static switch, but a 4-stage cycle: (1) Struggle (conscious loading and working memory overload), (2) Release (subconscious incubation), (3) Flow (optimal execution), and (4) Recovery (neurochemical replenishment).
Deliberate Play vs. Deliberate Practice [00:25:05]: Deliberate practice (repetition with incremental refinement) works only in bounded domains (math, violin). Deliberate play (repetition with improvisation) superiorly triggers neurochemical tagging for memory consolidation in open domains.
The Motivation Stack [00:26:39]: Human motivation scales hierarchically from Curiosity (small dopamine) $\rightarrow$ Passion (curiosity intersections) $\rightarrow$ Purpose (passion linked to cause, triggering serotonin, oxytocin, endorphins).
Autonomy-Attention Coupling [00:17:21]: Neurological coupling between agency and focus. Maximum attentional control cannot be mobilized without perceived intrinsic autonomy over the activity.
The Prediction Engine & Pattern Stocking [00:35:28]: The brain functions as a prediction engine optimizing energy conservation. Reading 25+ pages daily stocks the pattern recognition engine to accelerate creative breakthroughs.
Parrish's Learning Loop [00:42:01]: The cognitive progression: Experience $\rightarrow$ Reflection $\rightarrow$ Compression $\rightarrow$ Action. Consuming compressions alone creates an illusion of knowledge lacking operational depth.
Context: Used to illustrate the subjective sense of control during high-level flow.
Narrative: While spectators see Michael Jordan performing an extraordinary windmill dunk, Jordan's internal subjective experience in flow is feeling that the basketball rim is as wide as a hula hoop and that missing is impossible.
Context: Told to explain how the Flow Research Collective field-tested the 4% challenge-skills sweet spot.
Narrative: Kotler's team measured exact jump feature dimensions on downhill bike courses to isolate 4% progression increments. Riders who stayed strictly within this 4% challenge window never hit performance plateaus across an entire season.
The Finnish Patron Saint of Ice Skating [00:45:27]:
Context: Told to demonstrate how deep pre-interview research builds instant rapport with elite subjects.
Narrative: When interviewing a Finnish vodka executive, Kotler researched his hometown and discovered the patron saint of the town (Saint Lidwina/Seduina, patron saint of ice skating). Opening with hyper-specific personal trivia immediately established trust.
Josh Waitzkin’s Tai Chi & Surfing Journey [00:47:59]:
Context: Used to demonstrate metacognition and comfort with public failure.
Narrative: Chess prodigy Josh Waitzkin transitioned into competitive Tai Chi Push Hands, where thinking errors resulted in instant physical ejection from the ring. Later, he moved to Costa Rica to learn surfing in total obscurity away from public scrutiny.
Context: Told to illustrate how flow states trigger autoimmune recovery and nervous system resets.
Narrative: Bedridden for 3 years with Lyme disease and functional at only 10%, Kotler was dragged to the ocean by a friend. Popping up on a single wave triggered a macro flow state that cleared his brain fog and pain, eventually restoring 80% of his function over 6 months of surfing.
Context: Shared to highlight systemic flaws in medical diagnosis for long-term autoimmune conditions.
Narrative: Parrish woke up with total left-side facial paralysis. ER doctors insisted he was having a heart attack. After 6 hours of waiting, doctors dismissed his symptoms with prednisone, missing severe Lyme disease until a friend insisted on proper testing.
Context: Used to illustrate spite as a high-octane away-from motivator.
Narrative: Tom Brady's legendary NFL career was driven by the draft chip on his shoulder. Kotler keeps a fortune cookie taped to his fridge stating "You get great satisfaction out of proving other people wrong" to harness controlled "small-s spite."
6. References & Recommendations
Books
The Rise of Superman by Steven Kotler [00:41:24] - Explores peak performance and flow in action sports; required 15 years of research.
Gnar Country by Steven Kotler [00:24:23] - Documents an experiment in aging, longevity, and high-tempo skill acquisition.
West of Jesus by Steven Kotler [01:03:26] - Chronicles Kotler's neurological journey and recovery from Lyme disease through surfing.
Incognito: The Secret Lives of the Brain by David Eagleman [00:46:20] - Referenced regarding neuroscientific research on synesthesia and perception.
The Body Keeps the Score by Bessel van der Kolk [00:30:22] - Cited as a problematic text directly rebutted by Kotler's research paper.
The Breakout Principle by Dr. Herb Benson [00:58:34] - Outlines how flow state entry triggers nitric oxide release and spontaneous healing.
People
Mihaly Csikszentmihalyi [00:01:03] - Pioneering psychologist who scientifically defined flow state and its 6 characteristics.
Anders Ericsson [00:24:34] - Performance psychologist known for deliberate practice research; contrasted with deliberate play.
Malcolm Gladwell [00:24:53] - Popularized the "10,000-hour rule," described by Kotler as a gross oversimplification.
Dr. Ned Hallowell [00:16:31] - Harvard psychologist who coined modern ADHD concepts; frames ADHD as hyperflow.
Cal Newport [00:31:41] - Author of Deep Work; critiqued for rebranding flow state concepts.
Dr. Colleen Seifert [00:32:53] - University of Michigan researcher who proved working memory overload drives creative breakthroughs.
Josh Waitzkin [00:47:31] - Author of The Art of Learning, martial artist, and chess prodigy highlighted for elite metacognition.
Dr. Herb Benson [00:58:21] - Harvard cardiologist who mapped the neurochemistry of the relaxation response and flow cycle.
Dr. David Eagleman [00:46:20] - Neuroscientist and science communicator used as an example of domain-specific interviewing.
Tom Brady [00:28:40] - Seven-time Super Bowl champion NFL quarterback cited as an exemplar of spite-driven motivation.
Michael Jordan [00:02:03] - NBA legend used to illustrate subjective flow perception and the dark side of post-career spite.
Organizations & Geopolitical Institutions
Flow Research Collective [00:04:34] - Kotler's research organization that trained 35,000+ individuals in flow state optimization.
DARPA (Defense Advanced Research Projects Agency) [00:00:41] - Conducted research proving flow accelerates skill learning speed by 230%.
Harvard University [00:16:35] - Academic institution associated with Dr. Ned Hallowell and Dr. Ellen Langer.
Google [00:10:19] - Partnered with Csikszentmihalyi to mathematically model the 4% challenge-skills sweet spot.
Publications & Media
Frontiers in Neuroscience [00:30:18] - Published Kotler's paper "The Body Doesn't Keep the Score".
Nature [00:33:18] - Published Kotler's neurodynamical intuition study "Pathfinding".
Wired Magazine [00:18:56] - Benchmark publication used as a learning model for narrative structure.
7. Data & Figures
Data Point
Value
Context
Timestamp
DARPA Learning Acceleration
230% faster
Increase in learning velocity recorded in flow state during military tests
Geography and the wealth of nations ft. Prof. Jeffrey D Sachs | 27 Oct 2026 | LSE Event
"The discovery of America, and that of a passage to the East Indies by the Cape of Good Hope, are the two greatest and most important events recorded in the history of mankind." Adam Smith quoted by Jeffrey Sachs 00:18:43 http://www.youtub…
Primary Flow Activity Time
2 to 4 hours/week
Minimum weekly time required in primary flow activity to maintain health benefits